從查詢建立 DataTable (LINQ to DataSet)

文章
05/22/2023

資料繫結 (Data Binding) 是 DataTable 物件的常見用法。 CopyToDataTable 方法會採用查詢的結果並將資料複製到 DataTable 中，然後此物件便可用於資料繫結。執行了資料作業之後，新的 DataTable 就會合併回來源 DataTable 中。

CopyToDataTable 方法會使用下列程序，從查詢中建立 DataTable：

CopyToDataTable 方法會從來源資料表 (實作 DataTable 介面的 DataTable 物件) 中複製 (Clone) IQueryable<T>。 IEnumerable 來源通常源自 LINQ to DataSet 運算式或方法查詢。
複製的 DataTable 結構描述是根據來源資料表中第一個列舉 DataRow 物件的資料行所建立，而且複製之資料表的名稱就是來源資料表的名稱並附加上 "query" 一字。
若為來源資料表中的每個資料列，資料列的內容會複製到新的 DataRow 物件中，然後該物件便插入複製的資料表中。在複製作業中，RowState 和 RowError 屬性會保留下來。如果來源中的 ArgumentException 物件來自於不同的資料表，系統就會擲回 DataRow。
在輸入可查詢資料表中的所有 DataTable 物件都已經複製之後，就會傳回複製的 DataRow。如果來源序列 (Sequence) 沒有包含任何 DataRow 物件，此方法就會傳回空的 DataTable。

呼叫 CopyToDataTable 方法會導致系統執行與來源資料表繫結的查詢。

當 CopyToDataTable 方法在來源資料表的資料列中遇到 Null 參考或可為 Null 的實值型別 (Value Type) 時，它會將此值取代成 Value。如此一來，傳回之 DataTable 中的 Null 值都會經過正確處理。

注意：CopyToDataTable 方法會接受可從多個 DataTable 或 DataSet 物件傳回資料列的查詢當做輸入。 CopyToDataTable 方法會將資料 (但不包含屬性) 從來源 DataTable 或 DataSet 物件複製到傳回的 DataTable。您必須針對傳回的 DataTable 明確設定屬性，例如 Locale 和 TableName。

下列範例將在 SalesOrderHeader 資料表中查詢是否有 2001 年 8 月 8 日之後的訂單，然後使用 CopyToDataTable 方法，從該查詢中建立 DataTable。接著，DataTable 便繫結至 BindingSource，而它會當做 DataGridView 的 Proxy。

// Bind the System.Windows.Forms.DataGridView object
// to the System.Windows.Forms.BindingSource object.
dataGridView.DataSource = bindingSource;

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable orders = ds.Tables["SalesOrderHeader"];

// Query the SalesOrderHeader table for orders placed
// after August 8, 2001.
IEnumerable<DataRow> query =
    from order in orders.AsEnumerable()
    where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
    select order;

// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();

// Bind the table to a System.Windows.Forms.BindingSource object,
// which acts as a proxy for a System.Windows.Forms.DataGridView object.
bindingSource.DataSource = boundTable;

' Bind the System.Windows.Forms.DataGridView object
' to the System.Windows.Forms.BindingSource object.
dataGridView.DataSource = bindingSource

' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim orders As DataTable = ds.Tables("SalesOrderHeader")

' Query the SalesOrderHeader table for orders placed
'  after August 8, 2001.
Dim query = _
    From order In orders.AsEnumerable() _
    Where order.Field(Of DateTime)("OrderDate") > New DateTime(2001, 8, 1) _
    Select order

' Create a table from the query.
Dim boundTable As DataTable = query.CopyToDataTable()

' Bind the table to a System.Windows.Forms.BindingSource object,
' which acts as a proxy for a System.Windows.Forms.DataGridView object.
bindingSource.DataSource = boundTable

建立自訂 CopyToDataTable<T> 方法

現有的 CopyToDataTable 方法只能在通用參數 IEnumerable<T> 為 T 型別的DataRow 來源上運作。雖然這樣非常有用，但是資料表卻無法從一序列的純量型別、傳回匿名型別的查詢或執行資料表聯結的查詢建立。如需如何實作從純量或匿名型別載入資料表的兩個自訂 CopyToDataTable 方法範例，請參閱做法：實作 CopyToDataTable<T>，這時的泛型型別 T 不是 DataRow。

本節的範例都使用以下自訂型別：

public class Item
{
    public int Id { get; set; }
    public double Price { get; set; }
    public string Genre { get; set; }
}

public class Book : Item
{
    public string Author { get; set; }
}

public class Movie : Item
{
    public string Director { get; set; }
}

Public Class Item
    Private _Id As Int32
    Private _Price As Double
    Private _Genre As String

    Public Property Id() As Int32
        Get
            Return Id
        End Get
        Set(ByVal value As Int32)
            _Id = value
        End Set
    End Property

    Public Property Price() As Double
        Get
            Return _Price
        End Get
        Set(ByVal value As Double)
            _Price = value
        End Set
    End Property

    Public Property Genre() As String
        Get
            Return _Genre
        End Get
        Set(ByVal value As String)
            _Genre = value
        End Set
    End Property

End Class
Public Class Book
    Inherits Item
    Private _Author As String
    Public Property Author() As String
        Get
            Return _Author
        End Get
        Set(ByVal value As String)
            _Author = value
        End Set
    End Property
End Class

Public Class Movie
    Inherits Item
    Private _Director As String
    Public Property Director() As String
        Get
            Return _Director
        End Get
        Set(ByVal value As String)
            _Director = value
        End Set
    End Property

End Class

範例

此範例會執行 SalesOrderHeader 和 SalesOrderDetail 資料表的聯結，以取得八月的線上訂單資訊並根據此查詢建立資料表。

// Fill the DataSet.
var ds = new DataSet
{
    Locale = CultureInfo.InvariantCulture
};
FillDataSet(ds);

DataTable orders = ds.Tables["SalesOrderHeader"];
DataTable details = ds.Tables["SalesOrderDetail"];

var query =
    from order in orders.AsEnumerable()
    join detail in details.AsEnumerable()
    on order.Field<int>("SalesOrderID") equals
        detail.Field<int>("SalesOrderID")
    where order.Field<bool>("OnlineOrderFlag")
        && order.Field<DateTime>("OrderDate").Month == 8
    select new
    {
        SalesOrderID =
            order.Field<int>("SalesOrderID"),
        SalesOrderDetailID =
            detail.Field<int>("SalesOrderDetailID"),
        OrderDate =
            order.Field<DateTime>("OrderDate"),
        ProductID =
            detail.Field<int>("ProductID")
    };

DataTable orderTable = query.CopyToDataTable();

' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim details As DataTable = ds.Tables("SalesOrderDetail")


Dim query = _
    From order In orders.AsEnumerable() _
    Join detail In details.AsEnumerable() _
    On order.Field(Of Integer)("SalesOrderID") Equals _
            detail.Field(Of Integer)("SalesOrderID") _
    Where order.Field(Of Boolean)("OnlineOrderFlag") = True And _
            order.Field(Of DateTime)("OrderDate").Month = 8 _
    Select New With _
    { _
        .SalesOrderID = order.Field(Of Integer)("SalesOrderID"), _
        .SalesOrderDetailID = detail.Field(Of Integer)("SalesOrderDetailID"), _
        .OrderDate = order.Field(Of DateTime)("OrderDate"), _
        .ProductID = detail.Field(Of Integer)("ProductID") _
    }

Dim table As DataTable = query.CopyToDataTable()

範例

下列範例會查詢集合中價格大於 $9.99 的項目，並根據查詢結果建立資料表。

// Create a sequence.
var items = new Item[]
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"},
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Query for items with price greater than 9.99.
IOrderedEnumerable<Item> query = from i in items
                                 where i.Price > 9.99
                                 orderby i.Price
                                 select i;

// Load the query results into new DataTable.
DataTable table = query.CopyToDataTable();

Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Query for items with price greater than 9.99.
Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

Dim table As DataTable
table = query.CopyToDataTable()

範例

下列範例會查詢集合中價格大於 $9.99 的項目並擲回結果。所傳回的匿名型別序列就會載入到現有的資料表中。

// Create a sequence.
var items = new Item[]
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"},
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Create a table with a schema that matches that of the query results.
var table = new DataTable();
table.Columns.Add("Price", typeof(int));
table.Columns.Add("Genre", typeof(string));

var query = from i in items
            where i.Price > 9.99
            orderby i.Price
            select new { i.Price, i.Genre };

query.CopyToDataTable(table, LoadOption.PreserveChanges);

Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Create a table with a schema that matches that of the query results.
Dim table As DataTable = New DataTable()
table.Columns.Add("Price", GetType(Integer))
table.Columns.Add("Genre", GetType(String))

' Query for items with price greater than 9.99.
Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

query.CopyToDataTable(table, LoadOption.PreserveChanges)

範例

下列範例會查詢集合中價格大於 $9.99 的項目並擲回結果。所傳回的匿名型別序列就會載入到現有的資料表中。因為 Book 和 Movies 型別是衍生自 Item 型別，所以資料表結構描述會自動展開。

// Create a sequence.
var items = new Item[]
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"},
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Load into an existing DataTable, expand the schema and
// autogenerate a new Id.
var table = new DataTable();
DataColumn dc = table.Columns.Add("NewId", typeof(int));
dc.AutoIncrement = true;
table.Columns.Add("ExtraColumn", typeof(string));

var query = from i in items
            where i.Price > 9.99
            orderby i.Price
            select new { i.Price, i.Genre };

query.CopyToDataTable(table, LoadOption.PreserveChanges);

Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Load into an existing DataTable, expand the schema and
' autogenerate a new Id.
Dim table As DataTable = New DataTable()
Dim dc As DataColumn = table.Columns.Add("NewId", GetType(Integer))
dc.AutoIncrement = True
table.Columns.Add("ExtraColumn", GetType(String))

Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

query.CopyToDataTable(table, LoadOption.PreserveChanges)

範例

下列範例會查詢集合中價格大於 $9.99 的項目並傳回結果 Double 序列，這序列會在入到新資料表中。

// Create a sequence.
var items = new Item[]
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"},
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// load sequence of scalars.
IEnumerable<double> query = from i in items
                            where i.Price > 9.99
                            orderby i.Price
                            select i.Price;

DataTable table = query.CopyToDataTable();

Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select i.Price

Dim table As DataTable
table = query.CopyToDataTable()

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從查詢建立 DataTable (LINQ to DataSet)

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