DataTable.Load 方法

定义

命名空间:: System.Data

程序集:: netstandard.dll, System.Data.Common.dll

程序集:: System.Data.Common.dll

程序集:: System.Data.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

DataTable使用提供的IDataReader数据源中的值填充值。 DataTable如果已包含行，则数据源中的传入数据将与现有行合并。

重载

名称	说明
Load(IDataReader)	DataTable使用提供的IDataReader数据源中的值填充值。 DataTable如果已包含行，则数据源中的传入数据将与现有行合并。
Load(IDataReader, LoadOption)	DataTable使用提供的IDataReader数据源中的值填充值。 `DataTable`如果已包含行，则数据源中的传入数据会根据参数的值`loadOption`与现有行合并。
Load(IDataReader, LoadOption, FillErrorEventHandler)	DataTable使用错误处理委托提供的IDataReader数据源中的值填充值。

示例

以下示例演示了调用 Load 该方法所涉及的几个问题。首先，该示例侧重于架构问题，包括从加载 IDataReader的架构推断架构，然后处理不兼容的架构，以及缺少或附加列的架构。然后，该示例重点介绍数据问题，包括处理各种加载选项。

注释

此示例演示如何使用其中一个重载版本的 Load. 有关可能提供的其他示例，请参阅各个重载主题。

static void Main()
{
    // This example examines a number of scenarios involving the
    // DataTable.Load method.
    Console.WriteLine("Load a DataTable and infer its schema:");

    // The table has no schema. The Load method will infer the
    // schema from the IDataReader:
    DataTable table = new DataTable();

    // Retrieve a data reader, based on the Customers data. In
    // an application, this data might be coming from a middle-tier
    // business object:
    DataTableReader reader = new DataTableReader(GetCustomers());

    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine("Load a DataTable from an incompatible IDataReader:");

    // Create a table with a single integer column. Attempt
    // to load data from a reader with a schema that is
    // incompatible. Note the exception, determined
    // by the particular incompatibility:
    table = GetIntegerTable();
    reader = new DataTableReader(GetStringTable());
    try
    {
        table.Load(reader);
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.GetType().Name + ":" + ex.Message);
    }

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has extra columns:");

    // Note that loading a reader with extra columns adds
    // the columns to the existing table, if possible:
    table = GetIntegerTable();
    reader = new DataTableReader(GetCustomers());
    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has missing columns:");

    // Note that loading a reader with missing columns causes
    // the columns to be filled with null data, if possible:
    table = GetCustomers();
    reader = new DataTableReader(GetIntegerTable());
    table.Load(reader);
    PrintColumns(table);

    // Demonstrate the various possibilites when loading data into
    // a DataTable that already contains data.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Demonstrate data considerations:");
    Console.WriteLine("Current value, Original value, (RowState)");
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Original table:");

    table = SetupModifiedRows();
    DisplayRowState(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine("Data in IDataReader to be loaded:");
    DisplayRowState(GetChangedCustomers());

    PerformDemo(LoadOption.OverwriteChanges);
    PerformDemo(LoadOption.PreserveChanges);
    PerformDemo(LoadOption.Upsert);

    Console.WriteLine("Press any key to continue.");
    Console.ReadKey();
}

private static void DisplayRowState(DataTable table)
{
    for (int i = 0; i <= table.Rows.Count - 1; i++)
    {
        object current = "--";
        object original = "--";
        DataRowState rowState = table.Rows[i].RowState;

        // Attempt to retrieve the current value, which doesn't exist
        // for deleted rows:
        if (rowState != DataRowState.Deleted)
        {
            current = table.Rows[i]["Name", DataRowVersion.Current];
        }

        // Attempt to retrieve the original value, which doesn't exist
        // for added rows:
        if (rowState != DataRowState.Added)
        {
            original = table.Rows[i]["Name", DataRowVersion.Original];
        }
        Console.WriteLine("{0}: {1}, {2} ({3})", i, current,
            original, rowState);
    }
}

private static DataTable GetChangedCustomers()
{
    // Create sample Customers table.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 0, "XXX" });
    table.Rows.Add(new object[] { 1, "XXX" });
    table.Rows.Add(new object[] { 2, "XXX" });
    table.Rows.Add(new object[] { 3, "XXX" });
    table.Rows.Add(new object[] { 4, "XXX" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetCustomers()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 0, "Mary" });
    table.Rows.Add(new object[] { 1, "Andy" });
    table.Rows.Add(new object[] { 2, "Peter" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetIntegerTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 4 });
    table.Rows.Add(new object[] { 5 });
    table.AcceptChanges();
    return table;
}

private static DataTable GetStringTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { "Mary" });
    table.Rows.Add(new object[] { "Andy" });
    table.Rows.Add(new object[] { "Peter" });
    table.AcceptChanges();
    return table;
}

private static void PerformDemo(LoadOption optionForLoad)
{

    // Load data into a DataTable, retrieve a DataTableReader containing
    // different data, and call the Load method. Depending on the
    // LoadOption value passed as a parameter, this procedure displays
    // different results in the DataTable.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("table.Load(reader, {0})", optionForLoad);
    Console.WriteLine(" ============================= ");

    DataTable table = SetupModifiedRows();
    DataTableReader reader = new DataTableReader(GetChangedCustomers());
    table.RowChanging +=new DataRowChangeEventHandler(HandleRowChanging);

    table.Load(reader, optionForLoad);
    Console.WriteLine();
    DisplayRowState(table);
}

private static void PrintColumns(DataTable table)
{
    // Loop through all the rows in the DataTableReader
    foreach (DataRow row in table.Rows)
    {
        for (int i = 0; i < table.Columns.Count; i++)
        {
            Console.Write(row[i] + " ");
        }
        Console.WriteLine();
    }
}

private static DataTable SetupModifiedRows()
{
    // Fill a DataTable with customer info, and
    // then modify, delete, and add rows.

    DataTable table = GetCustomers();
    // Row 0 is unmodified.
    // Row 1 is modified.
    // Row 2 is deleted.
    // Row 3 is added.
    table.Rows[1]["Name"] = "Sydney";
    table.Rows[2].Delete();
    DataRow row = table.NewRow();
    row["ID"] = 3;
    row["Name"] = "Melony";
    table.Rows.Add(row);

    // Note that the code doesn't call
    // table.AcceptChanges()
    return table;
}

static void HandleRowChanging(object sender, DataRowChangeEventArgs e)
{
    Console.WriteLine(
        "RowChanging event: ID = {0}, action = {1}", e.Row["ID"],
        e.Action);
}

Sub Main()
  Dim table As New DataTable()

  ' This example examines a number of scenarios involving the 
  ' DataTable.Load method.
  Console.WriteLine("Load a DataTable and infer its schema:")

  ' Retrieve a data reader, based on the Customers data. In
  ' an application, this data might be coming from a middle-tier
  ' business object:
  Dim reader As New DataTableReader(GetCustomers())

  ' The table has no schema. The Load method will infer the 
  ' schema from the IDataReader:
  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine("Load a DataTable from an incompatible IDataReader:")

  ' Create a table with a single integer column. Attempt
  ' to load data from a reader with a schema that is 
  ' incompatible. Note the exception, determined
  ' by the particular incompatibility:
  table = GetIntegerTable()
  reader = New DataTableReader(GetStringTable())
  Try
    table.Load(reader)
  Catch ex As Exception
    Console.WriteLine(ex.GetType.Name & ":" & ex.Message())
  End Try

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable with an IDataReader that has extra columns:")

  ' Note that loading a reader with extra columns adds
  ' the columns to the existing table, if possible:
  table = GetIntegerTable()
  reader = New DataTableReader(GetCustomers())
  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable with an IDataReader that has missing columns:")

  ' Note that loading a reader with missing columns causes 
  ' the columns to be filled with null data, if possible:
  table = GetCustomers()
  reader = New DataTableReader(GetIntegerTable())
  table.Load(reader)
  PrintColumns(table)

  ' Demonstrate the various possibilites when loading data into
  ' a DataTable that already contains data.
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Demonstrate data considerations:")
  Console.WriteLine("Current value, Original value, (RowState)")
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Original table:")

  table = SetupModifiedRows()
  DisplayRowState(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine("Data in IDataReader to be loaded:")
  DisplayRowState(GetChangedCustomers())

  PerformDemo(LoadOption.OverwriteChanges)
  PerformDemo(LoadOption.PreserveChanges)
  PerformDemo(LoadOption.Upsert)

  Console.WriteLine("Press any key to continue.")
  Console.ReadKey()
End Sub

Private Sub DisplayRowState(ByVal table As DataTable)
  For i As Integer = 0 To table.Rows.Count - 1
    Dim current As Object = "--"
    Dim original As Object = "--"
    Dim rowState As DataRowState = table.Rows(i).RowState

    ' Attempt to retrieve the current value, which doesn't exist
    ' for deleted rows:
    If rowState <> DataRowState.Deleted Then
      current = table.Rows(i)("Name", DataRowVersion.Current)
    End If

    ' Attempt to retrieve the original value, which doesn't exist
    ' for added rows:
    If rowState <> DataRowState.Added Then
      original = table.Rows(i)("Name", DataRowVersion.Original)
    End If
    Console.WriteLine("{0}: {1}, {2} ({3})", i, current, original, rowState)
  Next
End Sub

Private Function GetChangedCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {0, "XXX"})
  table.Rows.Add(New Object() {1, "XXX"})
  table.Rows.Add(New Object() {2, "XXX"})
  table.Rows.Add(New Object() {3, "XXX"})
  table.Rows.Add(New Object() {4, "XXX"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {0, "Mary"})
  table.Rows.Add(New Object() {1, "Andy"})
  table.Rows.Add(New Object() {2, "Peter"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetIntegerTable() As DataTable
  ' Create sample table with a single Int32 column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {4})
  table.Rows.Add(New Object() {5})
  table.AcceptChanges()
  Return table
End Function

Private Function GetStringTable() As DataTable
  ' Create sample table with a single String column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {"Mary"})
  table.Rows.Add(New Object() {"Andy"})
  table.Rows.Add(New Object() {"Peter"})
  table.AcceptChanges()
  Return table
End Function

Private Sub PerformDemo(ByVal optionForLoad As LoadOption)

  ' Load data into a DataTable, retrieve a DataTableReader containing
  ' different data, and call the Load method. Depending on the
  ' LoadOption value passed as a parameter, this procedure displays
  ' different results in the DataTable.
  Console.WriteLine(" ============================= ")
  Console.WriteLine("table.Load(reader, {0})", optionForLoad)
  Console.WriteLine(" ============================= ")

  Dim table As DataTable = SetupModifiedRows()
  Dim reader As New DataTableReader(GetChangedCustomers())
  AddHandler table.RowChanging, New _
      DataRowChangeEventHandler(AddressOf HandleRowChanging)

  table.Load(reader, optionForLoad)
  Console.WriteLine()
  DisplayRowState(table)
End Sub

Private Sub PrintColumns( _
   ByVal table As DataTable)

  ' Loop through all the rows in the DataTableReader.
  For Each row As DataRow In table.Rows
    For Each col As DataColumn In table.Columns
      Console.Write(row(col).ToString() & " ")
    Next
    Console.WriteLine()
  Next
End Sub

Private Function SetupModifiedRows() As DataTable
  ' Fill a DataTable with customer info, and 
  ' then modify, delete, and add rows.

  Dim table As DataTable = GetCustomers()
  ' Row 0 is unmodified.
  ' Row 1 is modified.
  ' Row 2 is deleted.
  ' Row 3 is added.
  table.Rows(1)("Name") = "Sydney"
  table.Rows(2).Delete()
  Dim row As DataRow = table.NewRow
  row("ID") = 3
  row("Name") = "Melony"
  table.Rows.Add(row)

  ' Note that the code doesn't call
  ' table.AcceptChanges()
  Return table
End Function

Private Sub HandleRowChanging(ByVal sender As Object, _
  ByVal e As System.Data.DataRowChangeEventArgs)
  Console.WriteLine( _
      "RowChanging event: ID = {0}, action = {1}", e.Row("ID"), _
      e.Action)
End Sub

注解

该方法 Load 可用于几种常见方案，这些方案都集中在从指定数据源获取数据并将其添加到当前数据容器（在本例中为 a DataTable）。这些方案描述了其 DataTable更新和合并行为的标准用法。

与 DataTable 单个主数据源同步或更新。跟踪 DataTable 更改，允许与主数据源同步。此外，还可以 DataTable 接受来自一个或多个辅助数据源的增量数据。不 DataTable 负责跟踪更改，以便允许与辅助数据源同步。

鉴于这两个假设数据源，用户可能需要以下行为之一：

从主数据源初始化 DataTable 。在此方案中，用户希望使用主数据源中的值初始化空 DataTable 。稍后，用户打算将更改传播回主数据源。
保留更改并从主数据源重新同步。在此方案中，用户希望获取 DataTable 上一个方案中的填充内容，并执行与主数据源的增量同步，从而保留对主 DataTable数据源所做的修改。
辅助数据源中的增量数据馈送。在此方案中，用户希望合并来自一个或多个辅助数据源的更改，并将这些更改传播回主数据源。

该方法 Load 使所有这些方案成为可能。除了此方法的重载之一，还可以指定加载选项参数，指示合并中的 DataTable 行与正在加载的行的方式。（不允许你指定行为的重载使用默认加载选项。下表描述了枚举提供的三个 LoadOption 加载选项。在每个情况下，说明指示传入数据中某一行的主键与现有行的主键匹配时的行为。

加载选项	说明
`PreserveChanges`（默认值）	使用传入行的值更新行的原始版本。
`OverwriteChanges`	使用传入行的值更新行的当前版本和原始版本。
`Upsert`	使用传入行的值更新行的当前版本。

一般情况下，和PreserveChangesOverwriteChanges选项适用于用户需要将更改与其主要数据源同步DataSet的情况。该 Upsert 选项有助于聚合来自一个或多个辅助数据源的更改。

Load(IDataReader)

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

DataTable使用提供的IDataReader数据源中的值填充值。 DataTable如果已包含行，则数据源中的传入数据将与现有行合并。

public:
 void Load(System::Data::IDataReader ^ reader);

[System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Members from types used in the expression column to be trimmed if not referenced directly.")]
public void Load(System.Data.IDataReader reader);

public void Load(System.Data.IDataReader reader);

[<System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Members from types used in the expression column to be trimmed if not referenced directly.")>]
member this.Load : System.Data.IDataReader -> unit

member this.Load : System.Data.IDataReader -> unit

Public Sub Load (reader As IDataReader)

参数

reader: IDataReader

提供结果集的一 IDataReader 个。

属性: RequiresUnreferencedCodeAttribute

示例

以下示例演示了调用 Load 该方法所涉及的几个问题。首先，该示例侧重于架构问题，包括从加载 IDataReader的架构推断架构，然后处理不兼容的架构，以及缺少或附加列的架构。然后，该示例调用 Load 该方法，并在加载操作前后显示数据。

static void Main()
{
    // This example examines a number of scenarios involving the
    // DataTable.Load method.
    Console.WriteLine("Load a DataTable and infer its schema:");

    // The table has no schema. The Load method will infer the
    // schema from the IDataReader:
    DataTable table = new DataTable();

    // Retrieve a data reader, based on the Customers data. In
    // an application, this data might be coming from a middle-tier
    // business object:
    DataTableReader reader = new DataTableReader(GetCustomers());

    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable from an incompatible IDataReader:");

    // Create a table with a single integer column. Attempt
    // to load data from a reader with a schema that is
    // incompatible. Note the exception, determined
    // by the particular incompatibility:
    table = GetIntegerTable();
    reader = new DataTableReader(GetStringTable());
    try
    {
        table.Load(reader);
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.GetType().Name + ":" + ex.Message);
    }

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has extra columns:");

    // Note that loading a reader with extra columns adds
    // the columns to the existing table, if possible:
    table = GetIntegerTable();
    reader = new DataTableReader(GetCustomers());
    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has missing columns:");

    // Note that loading a reader with missing columns causes
    // the columns to be filled with null data, if possible:
    table = GetCustomers();
    reader = new DataTableReader(GetIntegerTable());
    table.Load(reader);
    PrintColumns(table);

    // Demonstrate the various possibilites when loading data
    // into a DataTable that already contains data.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Demonstrate data considerations:");
    Console.WriteLine("Current value, Original value, (RowState)");
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Original table:");

    table = SetupModifiedRows();
    DisplayRowState(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine("Data in IDataReader to be loaded:");
    DisplayRowState(GetChangedCustomers());

    // Load data into a DataTable, retrieve a DataTableReader
    // containing different data, and call the Load method.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("table.Load(reader)");
    Console.WriteLine(" ============================= ");

    table = SetupModifiedRows();
    reader = new DataTableReader(GetChangedCustomers());
    table.Load(reader);
    DisplayRowState(table);

    Console.WriteLine("Press any key to continue.");
    Console.ReadKey();
}

private static void DisplayRowState(DataTable table)
{
    for (int i = 0; i <= table.Rows.Count - 1; i++)
    {
        object current = "--";
        object original = "--";
        DataRowState rowState = table.Rows[i].RowState;

        // Attempt to retrieve the current value, which doesn't exist
        // for deleted rows:
        if (rowState != DataRowState.Deleted)
        {
            current = table.Rows[i]["Name", DataRowVersion.Current];
        }

        // Attempt to retrieve the original value, which doesn't exist
        // for added rows:
        if (rowState != DataRowState.Added)
        {
            original = table.Rows[i]["Name", DataRowVersion.Original];
        }
        Console.WriteLine("{0}: {1}, {2} ({3})", i,
            current, original, rowState);
    }
}

private static DataTable GetChangedCustomers()
{
    // Create sample Customers table.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID",
        typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 1, "XXX" });
    table.Rows.Add(new object[] { 2, "XXX" });
    table.Rows.Add(new object[] { 3, "XXX" });
    table.Rows.Add(new object[] { 4, "XXX" });
    table.Rows.Add(new object[] { 5, "XXX" });
    table.Rows.Add(new object[] { 6, "XXX" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetCustomers()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID",
        typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 1, "Mary" });
    table.Rows.Add(new object[] { 2, "Andy" });
    table.Rows.Add(new object[] { 3, "Peter" });
    table.Rows.Add(new object[] { 4, "Russ" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetIntegerTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID",
        typeof(int));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 5 });
    table.Rows.Add(new object[] { 6 });
    table.Rows.Add(new object[] { 7 });
    table.Rows.Add(new object[] { 8 });
    table.AcceptChanges();
    return table;
}

private static DataTable GetStringTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID",
        typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { "Mary" });
    table.Rows.Add(new object[] { "Andy" });
    table.Rows.Add(new object[] { "Peter" });
    table.Rows.Add(new object[] { "Russ" });
    table.AcceptChanges();
    return table;
}

private static void PrintColumns(DataTable table)
{
    // Loop through all the rows in the DataTableReader
    foreach (DataRow row in table.Rows)
    {
        for (int i = 0; i < table.Columns.Count; i++)
        {
            Console.Write(row[i] + " ");
        }
        Console.WriteLine();
    }
}

private static DataTable SetupModifiedRows()
{
    // Fill a DataTable with customer info, and
    // then modify, delete, and add rows.

    DataTable table = GetCustomers();
    // Row 0 is unmodified.
    // Row 1 is modified.
    // Row 2 is deleted.
    // Row 5 is added.
    table.Rows[1]["Name"] = "Sydney";
    table.Rows[2].Delete();
    DataRow row = table.NewRow();
    row["ID"] = 5;
    row["Name"] = "Melony";
    table.Rows.Add(row);

    // Note that the code doesn't call
    // table.AcceptChanges()
    return table;
}

Sub Main()
  ' This example examines a number of scenarios involving the 
  ' DataTable.Load method.
  Console.WriteLine("Load a DataTable and infer its schema:")

  ' The table has no schema. The Load method will infer the 
  ' schema from the IDataReader:
  Dim table As New DataTable()

  ' Retrieve a data reader, based on the Customers data. In
  ' an application, this data might be coming from a middle-tier
  ' business object:
  Dim reader As New DataTableReader(GetCustomers())

  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable from an incompatible IDataReader:")

  ' Create a table with a single integer column. Attempt
  ' to load data from a reader with a schema that is 
  ' incompatible. Note the exception, determined
  ' by the particular incompatibility:
  table = GetIntegerTable()
  reader = New DataTableReader(GetStringTable())
  Try
    table.Load(reader)
  Catch ex As Exception
    Console.WriteLine(ex.GetType.Name & ":" & ex.Message())
  End Try

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable with an IDataReader that has extra columns:")

  ' Note that loading a reader with extra columns adds
  ' the columns to the existing table, if possible:
  table = GetIntegerTable()
  reader = New DataTableReader(GetCustomers())
  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
      Console.WriteLine( _
          "Load a DataTable with an IDataReader that has missing columns:")

  ' Note that loading a reader with missing columns causes 
  ' the columns to be filled with null data, if possible:
  table = GetCustomers()
  reader = New DataTableReader(GetIntegerTable())
  table.Load(reader)
  PrintColumns(table)

  ' Demonstrate the various possibilites when loading data into
  ' a DataTable that already contains data.
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Demonstrate data considerations:")
  Console.WriteLine("Current value, Original value, (RowState)")
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Original table:")

  table = SetupModifiedRows()
  DisplayRowState(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine("Data in IDataReader to be loaded:")
  DisplayRowState(GetChangedCustomers())

  ' Load data into a DataTable, retrieve a DataTableReader 
  ' containing different data, and call the Load method. 
  Console.WriteLine(" ============================= ")
  Console.WriteLine("table.Load(reader)")
  Console.WriteLine(" ============================= ")

  table = SetupModifiedRows()
  reader = New DataTableReader(GetChangedCustomers())
  table.Load(reader)
  DisplayRowState(table)

  Console.WriteLine("Press any key to continue.")
  Console.ReadKey()
End Sub

Private Sub DisplayRowState(ByVal table As DataTable)
  For i As Integer = 0 To table.Rows.Count - 1
    Dim current As Object = "--"
    Dim original As Object = "--"
    Dim rowState As DataRowState = table.Rows(i).RowState

    ' Attempt to retrieve the current value, which doesn't exist
    ' for deleted rows:
    If rowState <> DataRowState.Deleted Then
      current = table.Rows(i)("Name", DataRowVersion.Current)
    End If

    ' Attempt to retrieve the original value, which doesn't exist
    ' for added rows:
    If rowState <> DataRowState.Added Then
      original = table.Rows(i)("Name", DataRowVersion.Original)
    End If
    Console.WriteLine("{0}: {1}, {2} ({3})", i, _
      current, original, rowState)
  Next
End Sub

Private Function GetChangedCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {1, "XXX"})
  table.Rows.Add(New Object() {2, "XXX"})
  table.Rows.Add(New Object() {3, "XXX"})
  table.Rows.Add(New Object() {4, "XXX"})
  table.Rows.Add(New Object() {5, "XXX"})
  table.Rows.Add(New Object() {6, "XXX"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {1, "Mary"})
  table.Rows.Add(New Object() {2, "Andy"})
  table.Rows.Add(New Object() {3, "Peter"})
  table.Rows.Add(New Object() {4, "Russ"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetIntegerTable() As DataTable
  ' Create sample table with a single Int32 column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {5})
  table.Rows.Add(New Object() {6})
  table.Rows.Add(New Object() {7})
  table.Rows.Add(New Object() {8})
  table.AcceptChanges()
  Return table
End Function

Private Function GetStringTable() As DataTable
  ' Create sample table with a single String column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {"Mary"})
  table.Rows.Add(New Object() {"Andy"})
  table.Rows.Add(New Object() {"Peter"})
  table.Rows.Add(New Object() {"Russ"})
  table.AcceptChanges()
  Return table
End Function

Private Sub PrintColumns( _
   ByVal table As DataTable)

  ' Loop through all the rows in the DataTableReader.
  For Each row As DataRow In table.Rows
    For Each col As DataColumn In table.Columns
      Console.Write(row(col).ToString() & " ")
    Next
    Console.WriteLine()
  Next
End Sub

Private Function SetupModifiedRows() As DataTable
  ' Fill a DataTable with customer info, and 
  ' then modify, delete, and add rows.

  Dim table As DataTable = GetCustomers()
  ' Row 0 is unmodified.
  ' Row 1 is modified.
  ' Row 2 is deleted.
  ' Row 5 is added.
  table.Rows(1)("Name") = "Sydney"
  table.Rows(2).Delete()
  Dim row As DataRow = table.NewRow
  row("ID") = 5
  row("Name") = "Melony"
  table.Rows.Add(row)

  ' Note that the code doesn't call
  ' table.AcceptChanges()
  Return table
End Function

注解

该方法 Load 使用加载 IDataReader的第一个结果集，成功完成后，将读取器的位置设置为下一个结果集（如果有）。转换数据时，该方法 Load 使用与该方法相同的转换规则 DbDataAdapter.Fill 。

从实例加载数据时，该方法 Load 必须考虑到三个 IDataReader 特定问题：架构、数据和事件操作。使用架构时，此方法 Load 可能会遇到如下表中所述的条件。架构操作针对所有导入的结果集进行，即使是包含无数据的结果集也是如此。

条件	行为
DataTable没有架构。	该方法 Load 根据导入 IDataReader的结果集推断架构。
该 DataTable 架构具有一个架构，但它与加载的架构不兼容。	该方法 Load 将引发与尝试将数据加载到不兼容架构时发生的特定错误对应的异常。
架构是兼容的，但加载的结果集架构包含不存在的 DataTable列。	该方法 Load 将额外列添加到 `DataTable`架构中。如果加载的结果集中的相应列 DataTable 与值不兼容，该方法将引发异常。该方法还会从所有已添加列的结果集中检索约束信息。除主键约束的情况外，仅当当前 DataTable 在加载操作开始时不包含任何列时，才会使用此约束信息。
架构是兼容的，但加载的结果集架构包含的列少于列 `DataTable`。	如果缺失列定义了默认值或列的数据类型可以为 null，则 Load 该方法允许添加行，替换缺失列的默认值或 `null` 值。如果没有默认值或 `null` 可以使用，则 `Load` 该方法将引发异常。如果未提供特定的默认值，该方法 `Load` 将使用 `null` 该值作为隐含默认值。

在考虑方法在数据操作方面的行为 Load 之前，请考虑每个列中的每一行 DataTable 都维护当前值和原始值。这些值可能等效，或者如果自填充 DataTable后行中的数据已更改，则这些值可能不同。有关详细信息，请参阅行状态和行版本。

此版本的 Load 方法尝试保留每行中的当前值，使原始值保持不变。（如果希望更好地控制传入数据的行为，请参阅 DataTable.Load。）如果现有行和传入行包含相应的主键值，则使用其当前行状态值处理该行，否则将被视为新行。

就事件操作而言，该 RowChanging 事件在每行更改之前发生，并在 RowChanged 每行更改后发生该事件。在每个情况下， Action 传递给事件处理程序的 DataRowChangeEventArgs 实例的属性包含与事件关联的特定操作的相关信息。此操作值取决于加载操作之前行的状态。在每个情况下，都会发生这两个事件，并且每个事件的操作都是相同的。该操作可以应用于每一行的当前版本或原始版本，也可以应用于这两者，具体取决于当前行状态。

下表显示了该方法的行为 Load 。最后一行（标记为“（不存在）”描述传入行的行为，这些行与任何现有行不匹配。此表中的每个单元格描述行内字段的当前值和原始值，以及 DataRowState 方法完成后的值 Load 。在这种情况下，该方法不允许你指示加载选项，并使用默认值 PreserveChanges。

现有 DataRowState	方法后 `Load` 的值和事件操作
已添加	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction = ChangeOriginal
已修改	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction = ChangeOriginal
已删除	当前 = <不可用> 原始 = <传入> 状态 = <已删除> RowAction = ChangeOriginal
不变	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal
（不存在）	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal

通过使用诸如和AutoIncrement等ReadOnly属性，可以约束 a DataColumn 中的值。该方法 Load 以与列属性定义的行为一致的方式处理此类列。对 a DataColumn 的只读约束仅适用于内存中发生的更改。如果需要，该方法 Load 将覆盖只读列值。

若要确定用于比较当前行与传入行的主键字段的版本，该方法 Load 使用行中主键值的原始版本（如果存在）。否则，该方法 Load 使用主键字段的当前版本。

另请参阅

适用于

Load(IDataReader, LoadOption)

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

DataTable使用提供的IDataReader数据源中的值填充值。 DataTable如果已包含行，则数据源中的传入数据会根据参数的值loadOption与现有行合并。

public:
 void Load(System::Data::IDataReader ^ reader, System::Data::LoadOption loadOption);

[System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Using LoadOption may cause members from types used in the expression column to be trimmed if not referenced directly.")]
public void Load(System.Data.IDataReader reader, System.Data.LoadOption loadOption);

public void Load(System.Data.IDataReader reader, System.Data.LoadOption loadOption);

[<System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Using LoadOption may cause members from types used in the expression column to be trimmed if not referenced directly.")>]
member this.Load : System.Data.IDataReader * System.Data.LoadOption -> unit

member this.Load : System.Data.IDataReader * System.Data.LoadOption -> unit

Public Sub Load (reader As IDataReader, loadOption As LoadOption)

参数

reader: IDataReader

IDataReader一个提供一个或多个结果集。

loadOption: LoadOption

枚举中的 LoadOption 一个值，该值指示已如何将行 DataTable 与共享同一主键的传入行组合在一起。

属性: RequiresUnreferencedCodeAttribute

示例

static void Main()
{
    // This example examines a number of scenarios involving the
    // DataTable.Load method.
    Console.WriteLine("Load a DataTable and infer its schema:");

    // The table has no schema. The Load method will infer the
    // schema from the IDataReader:
    DataTable table = new DataTable();

    // Retrieve a data reader, based on the Customers data. In
    // an application, this data might be coming from a middle-tier
    // business object:
    DataTableReader reader = new DataTableReader(GetCustomers());

    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable from an incompatible IDataReader:");

    // Create a table with a single integer column. Attempt
    // to load data from a reader with a schema that is
    // incompatible. Note the exception, determined
    // by the particular incompatibility:
    table = GetIntegerTable();
    reader = new DataTableReader(GetStringTable());
    try
    {
        table.Load(reader);
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.GetType().Name + ":" + ex.Message);
    }

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has extra columns:");

    // Note that loading a reader with extra columns adds
    // the columns to the existing table, if possible:
    table = GetIntegerTable();
    reader = new DataTableReader(GetCustomers());
    table.Load(reader);
    PrintColumns(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine(
        "Load a DataTable with an IDataReader that has missing columns:");

    // Note that loading a reader with missing columns causes
    // the columns to be filled with null data, if possible:
    table = GetCustomers();
    reader = new DataTableReader(GetIntegerTable());
    table.Load(reader);
    PrintColumns(table);

    // Demonstrate the various possibilites when loading data into
    // a DataTable that already contains data.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Demonstrate data considerations:");
    Console.WriteLine("Current value, Original value, (RowState)");
    Console.WriteLine(" ============================= ");
    Console.WriteLine("Original table:");

    table = SetupModifiedRows();
    DisplayRowState(table);

    Console.WriteLine(" ============================= ");
    Console.WriteLine("Data in IDataReader to be loaded:");
    DisplayRowState(GetChangedCustomers());

    PerformDemo(LoadOption.OverwriteChanges);
    PerformDemo(LoadOption.PreserveChanges);
    PerformDemo(LoadOption.Upsert);

    Console.WriteLine("Press any key to continue.");
    Console.ReadKey();
}

private static void DisplayRowState(DataTable table)
{
    for (int i = 0; i <= table.Rows.Count - 1; i++)
    {
        object current = "--";
        object original = "--";
        DataRowState rowState = table.Rows[i].RowState;

        // Attempt to retrieve the current value, which doesn't exist
        // for deleted rows:
        if (rowState != DataRowState.Deleted)
        {
            current = table.Rows[i]["Name", DataRowVersion.Current];
        }

        // Attempt to retrieve the original value, which doesn't exist
        // for added rows:
        if (rowState != DataRowState.Added)
        {
            original = table.Rows[i]["Name", DataRowVersion.Original];
        }
        Console.WriteLine("{0}: {1}, {2} ({3})", i,
            current, original, rowState);
    }
}

private static DataTable GetChangedCustomers()
{
    // Create sample Customers table.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 0, "XXX" });
    table.Rows.Add(new object[] { 1, "XXX" });
    table.Rows.Add(new object[] { 2, "XXX" });
    table.Rows.Add(new object[] { 3, "XXX" });
    table.Rows.Add(new object[] { 4, "XXX" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetCustomers()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));
    table.Columns.Add("Name", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 0, "Mary" });
    table.Rows.Add(new object[] { 1, "Andy" });
    table.Rows.Add(new object[] { 2, "Peter" });
    table.AcceptChanges();
    return table;
}

private static DataTable GetIntegerTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 4 });
    table.Rows.Add(new object[] { 5 });
    table.AcceptChanges();
    return table;
}

private static DataTable GetStringTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { "Mary" });
    table.Rows.Add(new object[] { "Andy" });
    table.Rows.Add(new object[] { "Peter" });
    table.AcceptChanges();
    return table;
}

private static void PerformDemo(LoadOption optionForLoad)
{

    // Load data into a DataTable, retrieve a DataTableReader containing
    // different data, and call the Load method. Depending on the
    // LoadOption value passed as a parameter, this procedure displays
    // different results in the DataTable.
    Console.WriteLine(" ============================= ");
    Console.WriteLine("table.Load(reader, {0})", optionForLoad);
    Console.WriteLine(" ============================= ");

    DataTable table = SetupModifiedRows();
    DataTableReader reader = new DataTableReader(GetChangedCustomers());
    table.RowChanging +=new DataRowChangeEventHandler(HandleRowChanging);

    table.Load(reader, optionForLoad);
    Console.WriteLine();
    DisplayRowState(table);
}

private static void PrintColumns(DataTable table)
{
    // Loop through all the rows in the DataTableReader
    foreach (DataRow row in table.Rows)
    {
        for (int i = 0; i < table.Columns.Count; i++)
        {
            Console.Write(row[i] + " ");
        }
        Console.WriteLine();
    }
}

private static DataTable SetupModifiedRows()
{
    // Fill a DataTable with customer info, and
    // then modify, delete, and add rows.

    DataTable table = GetCustomers();
    // Row 0 is unmodified.
    // Row 1 is modified.
    // Row 2 is deleted.
    // Row 3 is added.
    table.Rows[1]["Name"] = "Sydney";
    table.Rows[2].Delete();
    DataRow row = table.NewRow();
    row["ID"] = 3;
    row["Name"] = "Melony";
    table.Rows.Add(row);

    // Note that the code doesn't call
    // table.AcceptChanges()
    return table;
}

static void HandleRowChanging(object sender, DataRowChangeEventArgs e)
{
    Console.WriteLine(
        "RowChanging event: ID = {0}, action = {1}", e.Row["ID"], e.Action);
}

Sub Main()
  Dim table As New DataTable()

  ' This example examines a number of scenarios involving the
  '  DataTable.Load method.
  Console.WriteLine("Load a DataTable and infer its schema:")

  ' Retrieve a data reader, based on the Customers data. In
  ' an application, this data might be coming from a middle-tier
  ' business object:
  Dim reader As New DataTableReader(GetCustomers())

  ' The table has no schema. The Load method will infer the 
  ' schema from the IDataReader:
  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable from an incompatible IDataReader:")

  ' Create a table with a single integer column. Attempt
  ' to load data from a reader with a schema that is 
  ' incompatible. Note the exception, determined
  ' by the particular incompatibility:
  table = GetIntegerTable()
  reader = New DataTableReader(GetStringTable())
  Try
    table.Load(reader)
  Catch ex As Exception
    Console.WriteLine(ex.GetType.Name & ":" & ex.Message())
  End Try

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable with an IDataReader that has extra columns:")

  ' Note that loading a reader with extra columns adds
  ' the columns to the existing table, if possible:
  table = GetIntegerTable()
  reader = New DataTableReader(GetCustomers())
  table.Load(reader)
  PrintColumns(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine( _
      "Load a DataTable with an IDataReader that has missing columns:")

  ' Note that loading a reader with missing columns causes 
  ' the columns to be filled with null data, if possible:
  table = GetCustomers()
  reader = New DataTableReader(GetIntegerTable())
  table.Load(reader)
  PrintColumns(table)

  ' Demonstrate the various possibilites when loading data into
  ' a DataTable that already contains data.
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Demonstrate data considerations:")
  Console.WriteLine("Current value, Original value, (RowState)")
  Console.WriteLine(" ============================= ")
  Console.WriteLine("Original table:")

  table = SetupModifiedRows()
  DisplayRowState(table)

  Console.WriteLine(" ============================= ")
  Console.WriteLine("Data in IDataReader to be loaded:")
  DisplayRowState(GetChangedCustomers())

  PerformDemo(LoadOption.OverwriteChanges)
  PerformDemo(LoadOption.PreserveChanges)
  PerformDemo(LoadOption.Upsert)

  Console.WriteLine("Press any key to continue.")
  Console.ReadKey()
End Sub

Private Sub DisplayRowState(ByVal table As DataTable)
  For i As Integer = 0 To table.Rows.Count - 1
    Dim current As Object = "--"
    Dim original As Object = "--"
    Dim rowState As DataRowState = table.Rows(i).RowState

    ' Attempt to retrieve the current value, which doesn't exist
    ' for deleted rows:
    If rowState <> DataRowState.Deleted Then
      current = table.Rows(i)("Name", DataRowVersion.Current)
    End If

    ' Attempt to retrieve the original value, which doesn't exist
    ' for added rows:
    If rowState <> DataRowState.Added Then
      original = table.Rows(i)("Name", DataRowVersion.Original)
    End If
    Console.WriteLine("{0}: {1}, {2} ({3})", i, _
      current, original, rowState)
  Next
End Sub

Private Function GetChangedCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {0, "XXX"})
  table.Rows.Add(New Object() {1, "XXX"})
  table.Rows.Add(New Object() {2, "XXX"})
  table.Rows.Add(New Object() {3, "XXX"})
  table.Rows.Add(New Object() {4, "XXX"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetCustomers() As DataTable
  ' Create sample Customers table.
  Dim table As New DataTable

  ' Create two columns, ID and Name.
  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))
  table.Columns.Add("Name", GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {0, "Mary"})
  table.Rows.Add(New Object() {1, "Andy"})
  table.Rows.Add(New Object() {2, "Peter"})
  table.AcceptChanges()
  Return table
End Function

Private Function GetIntegerTable() As DataTable
  ' Create sample table with a single Int32 column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(Integer))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {4})
  table.Rows.Add(New Object() {5})
  table.AcceptChanges()
  Return table
End Function

Private Function GetStringTable() As DataTable
  ' Create sample table with a single String column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {"Mary"})
  table.Rows.Add(New Object() {"Andy"})
  table.Rows.Add(New Object() {"Peter"})
  table.AcceptChanges()
  Return table
End Function

Private Sub PerformDemo(ByVal optionForLoad As LoadOption)

  ' Load data into a DataTable, retrieve a DataTableReader containing
  ' different data, and call the Load method. Depending on the
  ' LoadOption value passed as a parameter, this procedure displays
  ' different results in the DataTable.
  Console.WriteLine(" ============================= ")
  Console.WriteLine("table.Load(reader, {0})", optionForLoad)
  Console.WriteLine(" ============================= ")

  Dim table As DataTable = SetupModifiedRows()
  Dim reader As New DataTableReader(GetChangedCustomers())
  AddHandler table.RowChanging, New _
      DataRowChangeEventHandler(AddressOf HandleRowChanging)

  table.Load(reader, optionForLoad)
  Console.WriteLine()
  DisplayRowState(table)
End Sub

Private Sub PrintColumns( _
   ByVal table As DataTable)

  ' Loop through all the rows in the DataTableReader.
  For Each row As DataRow In table.Rows
    For Each col As DataColumn In table.Columns
      Console.Write(row(col).ToString() & " ")
    Next
    Console.WriteLine()
  Next
End Sub

Private Function SetupModifiedRows() As DataTable
  ' Fill a DataTable with customer info, and 
  ' then modify, delete, and add rows.

  Dim table As DataTable = GetCustomers()
  ' Row 0 is unmodified.
  ' Row 1 is modified.
  ' Row 2 is deleted.
  ' Row 3 is added.
  table.Rows(1)("Name") = "Sydney"
  table.Rows(2).Delete()
  Dim row As DataRow = table.NewRow
  row("ID") = 3
  row("Name") = "Melony"
  table.Rows.Add(row)

  ' Note that the code doesn't call
  ' table.AcceptChanges()
  Return table
End Function

Private Sub HandleRowChanging(ByVal sender As Object, _
      ByVal e As System.Data.DataRowChangeEventArgs)
  Console.WriteLine( _
      "RowChanging event: ID = {0}, action = {1}", e.Row("ID"), e.Action)
End Sub

注解

该方法 Load 使用加载 IDataReader的第一个结果集，成功完成后，将读取器的位置设置为下一个结果集（如果有）。转换数据时，该方法 Load 使用与该方法相同的转换规则 Fill 。

从实例加载数据时，该方法 Load 必须考虑到三个 IDataReader 特定问题：架构、数据和事件操作。使用架构时，此方法 Load 可能会遇到如下表中所述的条件。架构操作针对所有导入的结果集进行，即使是包含无数据的结果集也是如此。

条件	行为
DataTable没有架构。	该方法 `Load` 根据导入 IDataReader的结果集推断架构。
该 DataTable 架构具有一个架构，但它与加载的架构不兼容。	该方法 `Load` 将引发与尝试将数据加载到不兼容架构时发生的特定错误对应的异常。
架构兼容，但加载的结果集架构包含不存在的 `DataTable`列。	该方法 `Load` 将额外列添加到 `DataTable`架构中。如果加载的结果集中的相应列 DataTable 与值不兼容，该方法将引发异常。该方法还会从所有已添加列的结果集中检索约束信息。除主键约束的情况外，仅当当前 DataTable 在加载操作开始时不包含任何列时，才会使用此约束信息。
架构是兼容的，但加载的结果集架构包含的列少于列 `DataTable`。	如果缺失列定义了默认值或列的数据类型可为 null，则 `Load` 该方法允许添加行，替换缺失列的默认值或 null 值。如果不能使用默认值或 null，则 `Load` 该方法将引发异常。如果未提供特定的默认值，该方法 `Load` 将使用 null 值作为隐含默认值。

在此方法调用中，指定的 LoadOption 参数会影响传入数据的处理。 Load 方法应如何处理与现有行具有相同主键的加载行？它应该修改当前值、原始值还是同时修改两者？这些问题等由 loadOption 参数控制。

如果现有行和传入行包含相应的主键值，则使用其当前行状态值处理该行，否则将被视为新行。

就事件操作而言，该 RowChanging 事件在每行更改之前发生，并在 RowChanged 每行更改后发生该事件。在每个情况下， Action 传递给事件处理程序的 DataRowChangeEventArgs 实例的属性包含与事件关联的特定操作的相关信息。此操作值因加载操作前行的状态而异。在每个情况下，都会发生这两个事件，并且每个事件的操作都是相同的。该操作可以应用于每一行的当前版本或原始版本，也可以应用于这两者，具体取决于当前行状态。

下表显示了使用每个 LoadOption 值调用时 Load 方法的行为，还显示值如何与所加载行的行状态交互。最后一行（标记为“（不存在）”描述传入行的行为，这些行与任何现有行不匹配。此表中的每个单元格描述行内字段的当前值和原始值，以及 DataRowState 方法完成后的值 Load 。

现有 DataRowState	Upsert	OverwriteChanges	PreserveChanges （默认行为）
已添加	当前 = <传入> Original = -<Not available> 状态 = <已添加> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction = ChangeOriginal
已修改	当前 = <传入> Original = <Existing> 状态 = <已修改> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction =ChangeOriginal
已删除	（加载不会影响已删除的行）当前 = --- Original = <Existing> 状态 = <已删除> （添加了具有以下特征的新行）当前 = <传入> 原始 = <不可用> 状态 = <已添加> RowAction = Add	撤消删除和当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <不可用> 原始 = <传入> 状态 = <已删除> RowAction = ChangeOriginal
不变	当前 = <传入> Original = <Existing> 如果新值与现有值相同，则状态 = <未更改> RowAction = Nothing 还状态 = <已修改> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal
不存在）	当前 = <传入> 原始 = <不可用> 状态 = <已添加> RowAction = Add	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal

如果在调用 Load 方法时指定 OverwriteChanges 或 PreserveChanges 选项，则假设传入的数据来自 DataTable主要数据源，而 DataTable 会跟踪更改，并且可以将更改传播回数据源。如果选择 Upsert 选项，则假定数据来自某个辅助数据源，例如中间层组件提供的数据（可能由用户更改）。在这种情况下，假设目的是聚合一个或多个数据源中的数据 DataTable，然后可能会将数据传播回主数据源。该 LoadOption 参数用于确定要用于主键比较的行的特定版本。下表提供了详细信息。

加载选项	用于主键比较的 DataRow 版本
`OverwriteChanges`	原始版本（如果存在）否则为当前版本
`PreserveChanges`	原始版本（如果存在）否则为当前版本
`Upsert`	当前版本（如果存在）否则为原始版本

另请参阅

适用于

Load(IDataReader, LoadOption, FillErrorEventHandler)

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

Source:: DataTable.cs

DataTable使用错误处理委托提供的IDataReader数据源中的值填充值。

public:
 virtual void Load(System::Data::IDataReader ^ reader, System::Data::LoadOption loadOption, System::Data::FillErrorEventHandler ^ errorHandler);

[System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Using LoadOption may cause members from types used in the expression column to be trimmed if not referenced directly.")]
public virtual void Load(System.Data.IDataReader reader, System.Data.LoadOption loadOption, System.Data.FillErrorEventHandler? errorHandler);

public virtual void Load(System.Data.IDataReader reader, System.Data.LoadOption loadOption, System.Data.FillErrorEventHandler? errorHandler);

public virtual void Load(System.Data.IDataReader reader, System.Data.LoadOption loadOption, System.Data.FillErrorEventHandler errorHandler);

[<System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Using LoadOption may cause members from types used in the expression column to be trimmed if not referenced directly.")>]
abstract member Load : System.Data.IDataReader * System.Data.LoadOption * System.Data.FillErrorEventHandler -> unit
override this.Load : System.Data.IDataReader * System.Data.LoadOption * System.Data.FillErrorEventHandler -> unit

abstract member Load : System.Data.IDataReader * System.Data.LoadOption * System.Data.FillErrorEventHandler -> unit
override this.Load : System.Data.IDataReader * System.Data.LoadOption * System.Data.FillErrorEventHandler -> unit

Public Overridable Sub Load (reader As IDataReader, loadOption As LoadOption, errorHandler As FillErrorEventHandler)

参数

reader: IDataReader

提供结果集的 A IDataReader 。

loadOption: LoadOption

枚举中的 LoadOption 一个值，该值指示已如何将行 DataTable 与共享同一主键的传入行组合在一起。

errorHandler: FillErrorEventHandler

FillErrorEventHandler加载数据时发生错误时要调用的委托。

属性: RequiresUnreferencedCodeAttribute

示例

static void Main()
{
    // Attempt to load data from a data reader in which
    // the schema is incompatible with the current schema.
    // If you use exception handling, you won't get the chance
    // to examine each row, and each individual table,
    // as the Load method progresses.
    // By taking advantage of the FillErrorEventHandler delegate,
    // you can interact with the Load process as an error occurs,
    // attempting to fix the problem, or simply continuing or quitting
    // the Load process:
    DataTable table = GetIntegerTable();
    DataTableReader reader = new DataTableReader(GetStringTable());
    table.Load(reader, LoadOption.OverwriteChanges, FillErrorHandler);

    Console.WriteLine("Press any key to continue.");
    Console.ReadKey();
}

private static DataTable GetIntegerTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(int));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { 4 });
    table.Rows.Add(new object[] { 5 });
    table.AcceptChanges();
    return table;
}

private static DataTable GetStringTable()
{
    // Create sample Customers table, in order
    // to demonstrate the behavior of the DataTableReader.
    DataTable table = new DataTable();

    // Create two columns, ID and Name.
    DataColumn idColumn = table.Columns.Add("ID", typeof(string));

    // Set the ID column as the primary key column.
    table.PrimaryKey = new DataColumn[] { idColumn };

    table.Rows.Add(new object[] { "Mary" });
    table.Rows.Add(new object[] { "Andy" });
    table.Rows.Add(new object[] { "Peter" });
    table.AcceptChanges();
    return table;
}

static void FillErrorHandler(object sender, FillErrorEventArgs e)
{
    // You can use the e.Errors value to determine exactly what
    // went wrong.
    if (e.Errors.GetType() == typeof(System.FormatException))
    {
        Console.WriteLine("Error when attempting to update the value: {0}",
            e.Values[0]);
    }

    // Setting e.Continue to True tells the Load
    // method to continue trying. Setting it to False
    // indicates that an error has occurred, and the
    // Load method raises the exception that got
    // you here.
    e.Continue = true;
}

Sub Main()
  Dim table As New DataTable()

  ' Attempt to load data from a data reader in which
  ' the schema is incompatible with the current schema.
  ' If you use exception handling, you won't get the chance
  ' to examine each row, and each individual table,
  ' as the Load method progresses.
  ' By taking advantage of the FillErrorEventHandler delegate,
  ' you can interact with the Load process as an error occurs,
  ' attempting to fix the problem, or simply continuing or quitting
  ' the Load process:
  table = GetIntegerTable()
  Dim reader As New DataTableReader(GetStringTable())
  table.Load(reader, LoadOption.OverwriteChanges, _
      AddressOf FillErrorHandler)

  Console.WriteLine("Press any key to continue.")
  Console.ReadKey()
End Sub

Private Sub FillErrorHandler(ByVal sender As Object, _
  ByVal e As FillErrorEventArgs)
  ' You can use the e.Errors value to determine exactly what
  ' went wrong.
  If e.Errors.GetType Is GetType(System.FormatException) Then
    Console.WriteLine("Error when attempting to update the value: {0}", _
      e.Values(0))
  End If

  ' Setting e.Continue to True tells the Load
  ' method to continue trying. Setting it to False
  ' indicates that an error has occurred, and the 
  ' Load method raises the exception that got 
  ' you here.
  e.Continue = True
End Sub

Private Function GetIntegerTable() As DataTable
  ' Create sample table with a single Int32 column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", GetType(Integer))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {4})
  table.Rows.Add(New Object() {5})
  table.TableName = "IntegerTable"
  table.AcceptChanges()
  Return table
End Function

Private Function GetStringTable() As DataTable
  ' Create sample table with a single String column.
  Dim table As New DataTable

  Dim idColumn As DataColumn = table.Columns.Add("ID", _
      GetType(String))

  ' Set the ID column as the primary key column.
  table.PrimaryKey = New DataColumn() {idColumn}

  table.Rows.Add(New Object() {"Mary"})
  table.Rows.Add(New Object() {"Andy"})
  table.Rows.Add(New Object() {"Peter"})
  table.AcceptChanges()
  Return table
End Function

Private Sub PrintColumns( _
   ByVal table As DataTable)

  ' Loop through all the rows in the DataTableReader.
  For Each row As DataRow In table.Rows
    For Each col As DataColumn In table.Columns
      Console.Write(row(col).ToString() & " ")
    Next
    Console.WriteLine()
  Next
End Sub

注解

该方法 Load 使用加载 IDataReader的第一个结果集，成功完成后，将读取器的位置设置为下一个结果集（如果有）。转换数据时，该方法 Load 使用与该方法相同的转换规则 DbDataAdapter.Fill 。

条件	行为
DataTable没有架构。	该方法 `Load` 根据导入 IDataReader的结果集推断架构。
该 DataTable 架构具有一个架构，但它与加载的架构不兼容。	该方法 `Load` 将引发与尝试将数据加载到不兼容架构时发生的特定错误对应的异常。
架构兼容，但加载的结果集架构包含不存在的 `DataTable`列。	该方法 `Load` 将额外列添加到 `DataTable`'s 架构中。如果加载的结果集中的相应列 DataTable 与值不兼容，该方法将引发异常。该方法还会从所有已添加列的结果集中检索约束信息。除主键约束的情况外，仅当当前 DataTable 在加载操作开始时不包含任何列时，才会使用此约束信息。
架构是兼容的，但加载的结果集架构包含的列少于列 `DataTable`。	如果缺失列定义了默认值或列的数据类型可为 null，则 `Load` 该方法允许添加行，替换缺失列的默认值或 null 值。如果不能使用默认值或 null，则 `Load` 该方法将引发异常。如果未提供特定的默认值，该方法 `Load` 将使用 null 值作为隐含默认值。

如果现有行和传入行包含相应的主键值，则使用其当前行状态值处理该行，否则将被视为新行。

现有 DataRowState	Upsert	OverwriteChanges	PreserveChanges （默认行为）
已添加	当前 = <传入> Original = -<Not available> 状态 = <已添加> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction = ChangeOriginal
已修改	当前 = <传入> Original = <Existing> 状态 = <已修改> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <现有> 原始 = <传入> 状态 = <已修改> RowAction =ChangeOriginal
eleted	（加载不会影响已删除的行）当前 = --- Original = <Existing> 状态 = <已删除> （添加了具有以下特征的新行）当前 = <传入> 原始 = <不可用> 状态 = <已添加> RowAction = Add	撤消删除和当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <不可用> 原始 = <传入> 状态 = <已删除> RowAction = ChangeOriginal
不变	当前 = <传入> Original = <Existing> 如果新值与现有值相同，则状态 = <未更改> RowAction = Nothing 还状态 = <已修改> RowAction = 更改	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal
不存在）	当前 = <传入> 原始 = <不可用> 状态 = <已添加> RowAction = Add	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal	当前 = <传入> 原始 = <传入> 状态 = <未更改> RowAction = ChangeCurrentAndOriginal

加载选项	用于主键比较的 DataRow 版本
`OverwriteChanges`	原始版本（如果存在）否则为当前版本
`PreserveChanges`	原始版本（如果存在）否则为当前版本
`Upsert`	当前版本（如果存在）否则为原始版本

该 errorHandler 参数是一个 FillErrorEventHandler 委托，它引用在加载数据时发生错误时调用的过程。 FillErrorEventArgs传递给过程的参数提供了属性，可用于检索有关所发生错误、当前数据行和DataTable正在填充的信息。使用此委托机制（而不是更简单的 try/catch 块）可以确定错误、处理情况，以及根据需要继续处理。该 FillErrorEventArgs 参数提供一个 Continue 属性：将此属性设置为 true 指示你已处理错误，并希望继续处理。将属性设置为 false 指示要停止处理。请注意，将属性设置为 false 导致触发问题的代码引发异常。

另请参阅

适用于

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