DataSet.Merge Method

Definition

Namespace:

System.Data

Assembly:

System.Data.Common.dll

Merges a specified DataSet, DataTable, or array of DataRow objects into the current DataSet or DataTable.

Overloads

Merge(DataRow[])	Merges an array of DataRow objects into the current DataSet.
Merge(DataSet)	Merges a specified DataSet and its schema into the current DataSet.
Merge(DataTable)	Merges a specified DataTable and its schema into the current DataSet.
Merge(DataSet, Boolean)	Merges a specified DataSet and its schema into the current DataSet, preserving or discarding any changes in this DataSet according to the given argument.
Merge(DataRow[], Boolean, MissingSchemaAction)	Merges an array of DataRow objects into the current DataSet, preserving or discarding changes in the DataSet and handling an incompatible schema according to the given arguments.
Merge(DataSet, Boolean, MissingSchemaAction)	Merges a specified DataSet and its schema with the current DataSet, preserving or discarding changes in the current DataSet and handling an incompatible schema according to the given arguments.
Merge(DataTable, Boolean, MissingSchemaAction)	Merges a specified DataTable and its schema into the current DataSet, preserving or discarding changes in the DataSet and handling an incompatible schema according to the given arguments.

Merge(DataRow[])

Source:

DataSet.cs

Merges an array of DataRow objects into the current DataSet.

public:
 void Merge(cli::array <System::Data::DataRow ^> ^ rows);

public void Merge (System.Data.DataRow[] rows);

member this.Merge : System.Data.DataRow[] -> unit

Public Sub Merge (rows As DataRow())

Parameters

rows

DataRow[]

The array of DataRow objects to be merged into the DataSet.

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of a merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• Using DataSets in ADO.NET

Merge(DataSet)

Source:

DataSet.cs

Merges a specified DataSet and its schema into the current DataSet.

public:
 void Merge(System::Data::DataSet ^ dataSet);

public void Merge (System.Data.DataSet dataSet);

member this.Merge : System.Data.DataSet -> unit

Public Sub Merge (dataSet As DataSet)

Parameters

dataSet

DataSet

The DataSet whose data and schema will be merged.

Exceptions

ConstraintException

One or more constraints cannot be enabled.

ArgumentNullException

The dataSet is null.

Examples

The following example uses the GetChanges, Update, and Merge methods on a DataSet.

private void DemonstrateMerge()
{
    // Create a DataSet with one table, two columns, and three rows.
    DataSet dataSet = new DataSet("dataSet");
    DataTable table = new DataTable("Items");
    DataColumn idColumn = new DataColumn("id",
        Type.GetType("System.Int32"));
    idColumn.AutoIncrement=true;
    DataColumn itemColumn = new DataColumn("Item",
        Type.GetType("System.Int32"));

    // DataColumn array to set primary key.
    DataColumn[] keyColumn= new DataColumn[1];
    DataRow row;

    // Create variable for temporary DataSet.
    DataSet changeDataSet;

    // Add columns to table, and table to DataSet.
    table.Columns.Add(idColumn);
    table.Columns.Add(itemColumn);
    dataSet.Tables.Add(table);

    // Set primary key column.
    keyColumn[0]= idColumn;
    table.PrimaryKey=keyColumn;

    // Add ten rows.
    for(int i = 0; i <10;i++)
    {
        row=table.NewRow();
        row["Item"]= i;
        table.Rows.Add(row);
    }

    // Accept changes.
    dataSet.AcceptChanges();
    PrintValues(dataSet, "Original values");

    // Change two row values.
    table.Rows[0]["Item"]= 50;
    table.Rows[1]["Item"]= 111;

    // Add one row.
    row=table.NewRow();
    row["Item"]=74;
    table.Rows.Add(row);

    // Insert code for error checking. Set one row in error.
    table.Rows[1].RowError= "over 100";
    PrintValues(dataSet, "Modified and New Values");
    // If the table has changes or errors, create a subset DataSet.
    if(dataSet.HasChanges(DataRowState.Modified |
        DataRowState.Added)& dataSet.HasErrors)
    {
        // Use GetChanges to extract subset.
        changeDataSet = dataSet.GetChanges(
            DataRowState.Modified|DataRowState.Added);
        PrintValues(changeDataSet, "Subset values");
        // Insert code to reconcile errors. In this case reject changes.
        foreach(DataTable changeTable in changeDataSet.Tables)
        {
            if (changeTable.HasErrors)
            {
                foreach(DataRow changeRow in changeTable.Rows)
                {
                    //Console.WriteLine(changeRow["Item"]);
                    if((int)changeRow["Item",
                        DataRowVersion.Current ]> 100)
                    {
                        changeRow.RejectChanges();
                        changeRow.ClearErrors();
                    }
                }
            }
        }
        PrintValues(changeDataSet, "Reconciled subset values");
        // Merge changes back to first DataSet.
        dataSet.Merge(changeDataSet);
        PrintValues(dataSet, "Merged Values");
    }
}

private void PrintValues(DataSet dataSet, string label)
{
    Console.WriteLine("\n" + label);
    foreach(DataTable table in dataSet.Tables)
    {
        Console.WriteLine("TableName: " + table.TableName);
        foreach(DataRow row in table.Rows)
        {
            foreach(DataColumn column in table.Columns)
            {
                Console.Write("\table " + row[column] );
            }
            Console.WriteLine();
        }
    }
}

 Private Sub DemonstrateMerge()
     ' Create a DataSet with one table, two columns, and three rows.
     Dim dataSet As New DataSet("dataSet")
     Dim table As New DataTable("Items")
     Dim idColumn As New DataColumn("id", Type.GetType("System.Int32"))
     idColumn.AutoIncrement = True
     Dim itemColumn As New DataColumn("Item", Type.GetType("System.Int32"))

     ' DataColumn array to set primary key.
     Dim keyColumn(0) As DataColumn
     Dim row As DataRow

     ' Create variable for temporary DataSet. 
     Dim changeDataSet As DataSet

     ' Add columns to table, and table to DataSet.   
     table.Columns.Add(idColumn)
     table.Columns.Add(itemColumn)
     dataSet.Tables.Add(table)

     ' Set primary key column.
     keyColumn(0) = idColumn
     table.PrimaryKey = keyColumn

     ' Add ten rows.
     Dim i As Integer
     For i = 0 To 9
         row = table.NewRow()
         row("Item") = i
         table.Rows.Add(row)
     Next i

     ' Accept changes.
     dataSet.AcceptChanges()
     PrintValues(dataSet, "Original values")

     ' Change two row values.
     table.Rows(0)("Item") = 50
     table.Rows(1)("Item") = 111

     ' Add one row.
     row = table.NewRow()
     row("Item") = 74
     table.Rows.Add(row)

     ' Insert code for error checking. Set one row in error.
     table.Rows(1).RowError = "over 100"
     PrintValues(dataSet, "Modified and New Values")

     ' If the table has changes or errors, create a subset DataSet.
     If dataSet.HasChanges(DataRowState.Modified Or DataRowState.Added) _
        And dataSet.HasErrors Then

         ' Use GetChanges to extract subset.
         changeDataSet = dataSet.GetChanges(DataRowState.Modified _
            Or DataRowState.Added)
         PrintValues(changeDataSet, "Subset values")

         ' Insert code to reconcile errors. In this case, reject changes.
         Dim changeTable As DataTable
         For Each changeTable In  changeDataSet.Tables
             If changeTable.HasErrors Then
                 Dim changeRow As DataRow
                 For Each changeRow In  changeTable.Rows
                     'Console.WriteLine(changeRow["Item"]);
                     If CInt(changeRow("Item", _
                        DataRowVersion.Current)) > 100 Then
                         changeRow.RejectChanges()
                         changeRow.ClearErrors()
                     End If
                 Next changeRow
             End If
         Next changeTable
         PrintValues(changeDataSet, "Reconciled subset values")

         ' Merge changes back to first DataSet.
         dataSet.Merge(changeDataSet)
         PrintValues(dataSet, "Merged Values")
     End If
 End Sub
 
Private Sub PrintValues(dataSet As DataSet, label As String)
     Console.WriteLine(ControlChars.Cr & label)
     Dim table As DataTable
     For Each table In  dataSet.Tables
         Console.WriteLine("TableName: " & table.TableName)
         Dim row As DataRow
         For Each row In  table.Rows
             Dim column As DataColumn
             For Each column In  table.Columns
                 Console.Write(ControlChars.Tab & " " _
                    & row(column).ToString())
             Next column
             Console.WriteLine()
         Next row
     Next table
End Sub

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• ForeignKeyConstraint
• GetChanges()
• UniqueConstraint
• Using DataSets in ADO.NET

Merge(DataTable)

Source:

DataSet.cs

Merges a specified DataTable and its schema into the current DataSet.

public:
 void Merge(System::Data::DataTable ^ table);

public void Merge (System.Data.DataTable table);

member this.Merge : System.Data.DataTable -> unit

Public Sub Merge (table As DataTable)

Parameters

table

DataTable

The DataTable whose data and schema will be merged.

Exceptions

ArgumentNullException

The table is null.

Examples

The following example creates a simple DataSet with one table, two columns, and ten rows. A second DataTable is created that is identical to the first. Two rows are added to the second table, which is then merged into the DataSet.

private void DemonstrateMergeTable()
{
    // Create a DataSet with one table, two columns, and ten rows.
    DataSet dataSet = new DataSet("dataSet");
    DataTable table = new DataTable("Items");

    // Add table to the DataSet
    dataSet.Tables.Add(table);

    // Add columns
    DataColumn c1 = new DataColumn("id",
        Type.GetType("System.Int32"),"");
    DataColumn c2 = new DataColumn("Item",
        Type.GetType("System.Int32"),"");
    table.Columns.Add(c1);
    table.Columns.Add(c2);

    // DataColumn array to set primary key.
    DataColumn[] keyCol= new DataColumn[1];

    // Set primary key column.
    keyCol[0]= c1;
    table.PrimaryKey=keyCol;

    // Add a RowChanged event handler for the table.
    table.RowChanged += new
        DataRowChangeEventHandler(Row_Changed);

    // Add ten rows.
    for(int i = 0; i <10;i++)
    {
        DataRow row=table.NewRow();
        row["id"] = i;
        row["Item"]= i;
        table.Rows.Add(row);
    }
    // Accept changes.
    dataSet.AcceptChanges();

    PrintValues(dataSet, "Original values");

    // Create a second DataTable identical to the first.
    DataTable t2 = table.Clone();

    // Add three rows. Note that the id column can'te be the
    // same as existing rows in the DataSet table.
    DataRow newRow;
    newRow = t2.NewRow();
    newRow["id"] = 14;
    newRow["item"] = 774;

    //Note the alternative method for adding rows.
    t2.Rows.Add(new Object[] { 12, 555 });
    t2.Rows.Add(new Object[] { 13, 665 });

    // Merge the table into the DataSet
    Console.WriteLine("Merging");
    dataSet.Merge(t2);
    PrintValues(dataSet, "Merged With table.");
}

private void Row_Changed(object sender,
    DataRowChangeEventArgs e)
{
    Console.WriteLine("Row Changed " + e.Action.ToString()
        + "\table" + e.Row.ItemArray[0]);
}

private void PrintValues(DataSet dataSet, string label)
{
    Console.WriteLine("\n" + label);
    foreach(DataTable table in dataSet.Tables)
    {
        Console.WriteLine("TableName: " + table.TableName);
        foreach(DataRow row in table.Rows)
        {
            foreach(DataColumn column in table.Columns)
            {
                Console.Write("\table " + row[column] );
            }
            Console.WriteLine();
        }
    }
}

Private Sub DemonstrateMergeTable()
    ' Create a DataSet with one table, two columns, 
    ' and ten rows.
    Dim dataSet As New DataSet("dataSet")
    Dim table As New DataTable("Items")

    ' Add tables to the DataSet
    dataSet.Tables.Add(table)

    ' Add columns
    Dim c1 As New DataColumn("id", Type.GetType("System.Int32"), "")
    Dim c2 As New DataColumn("Item", Type.GetType("System.Int32"), "")
    table.Columns.Add(c1)
    table.Columns.Add(c2)

    ' DataColumn array to set primary key.
    Dim keyCol(0) As DataColumn

    ' Set primary key column.
    keyCol(0) = c1
    table.PrimaryKey = keyCol

    ' Add RowChanged event handler for the table.
    AddHandler table.RowChanged, AddressOf Row_Changed

    ' Add ten rows.
    Dim i As Integer
    Dim row As DataRow

    For i = 0 To 9
        row = table.NewRow()
        row("id") = i
        row("Item") = i
        table.Rows.Add(row)
    Next i

    ' Accept changes.
    dataSet.AcceptChanges()
    PrintValues(dataSet, "Original values")

    ' Create a second DataTable identical to the first.
    Dim t2 As DataTable
    t2 = table.Clone()

    ' Add three rows. Note that the id column can't be the 
    ' same as existing rows in the DataSet table.
    Dim newRow As DataRow
    newRow = t2.NewRow()
    newRow("id") = 14
    newRow("Item") = 774
    t2.Rows.Add(newRow)

    newRow = t2.NewRow()
    newRow("id") = 12
    newRow("Item") = 555
    t2.Rows.Add(newRow)

    newRow = t2.NewRow()
    newRow("id") = 13
    newRow("Item") = 665
    t2.Rows.Add(newRow)

    ' Merge the table into the DataSet.
    Console.WriteLine("Merging")
    dataSet.Merge(t2)
    PrintValues(dataSet, "Merged With Table")
 End Sub 
     
 Private Sub Row_Changed( _
    sender As Object, e As DataRowChangeEventArgs)
     Console.WriteLine("Row Changed " & e.Action.ToString() _
        & ControlChars.Tab & e.Row.ItemArray(0).ToString())
 End Sub
 
 Private Sub PrintValues(dataSet As DataSet, label As String)
     Console.WriteLine(ControlChars.Cr & label)
     Dim table As DataTable
     Dim row As DataRow
     Dim column As DataColumn
     For Each table In  dataSet.Tables
         Console.WriteLine("TableName: " & table.TableName) 
         For Each row In  table.Rows             
             For Each column In  table.Columns
                 Console.Write(ControlChars.Tab & " " _
                    & row(column).ToString())
             Next column
             Console.WriteLine()
         Next row
     Next table
 End Sub

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• Using DataSets in ADO.NET

Merge(DataSet, Boolean)

Source:

DataSet.cs

Merges a specified DataSet and its schema into the current DataSet, preserving or discarding any changes in this DataSet according to the given argument.

public:
 void Merge(System::Data::DataSet ^ dataSet, bool preserveChanges);

public void Merge (System.Data.DataSet dataSet, bool preserveChanges);

member this.Merge : System.Data.DataSet * bool -> unit

Public Sub Merge (dataSet As DataSet, preserveChanges As Boolean)

Parameters

dataSet

DataSet

The DataSet whose data and schema will be merged.

preserveChanges

Boolean

true to preserve changes in the current DataSet; otherwise, false.

Examples

The following example creates a simple DataSet with one table, two columns, and ten rows. After adding ten rows, two values are changed, and one row is added. A subset of the changed data is created using the GetChanges method. After reconciling errors, the subset data is merged into the original DataSet.

private void DemonstrateMerge()
{
    // Create a DataSet with one table, two columns,
    // and three rows.
    DataSet dataSet = new DataSet("dataSet");
    DataTable table = new DataTable("Items");
    DataColumn idColumn = new DataColumn("id",
        Type.GetType("System.Int32"),"");
    idColumn.AutoIncrement=true;
    DataColumn itemColumn = new DataColumn("Item",
        Type.GetType("System.Int32"),"");

    // DataColumn array to set primary key.
    DataColumn[] keyColumn= new DataColumn[1];
    DataRow row;

    // Create variable for temporary DataSet.
    DataSet changesDataSet;

    // Add RowChanged event handler for the table.
    table.RowChanged+=new DataRowChangeEventHandler(
        Row_Changed);
    dataSet.Tables.Add(table);
    table.Columns.Add(idColumn);
    table.Columns.Add(itemColumn);

    // Set primary key column.
    keyColumn[0]= idColumn;
    table.PrimaryKey=keyColumn;
    // Add ten rows.
    for(int i = 0; i <10;i++)
    {
        row=table.NewRow();
        row["Item"]= i;
        table.Rows.Add(row);
    }
    // Accept changes.
    dataSet.AcceptChanges();
    PrintValues(dataSet, "Original values");

    // Change row values.
    table.Rows[0]["Item"]= 50;
    table.Rows[1]["Item"]= 111;

    // Add one row.
    row=table.NewRow();
    row["Item"]=74;
    table.Rows.Add(row);

    // Insert code for error checking. Set one row in error.
    table.Rows[1].RowError= "over 100";
    PrintValues(dataSet, "Modified and New Values");

    // If the table has changes or errors,
    // create a subset DataSet.
    if(dataSet.HasChanges(DataRowState.Modified |
        DataRowState.Added)&& dataSet.HasErrors)
    {
        // Use GetChanges to extract subset.
        changesDataSet = dataSet.GetChanges(
            DataRowState.Modified|DataRowState.Added);
        PrintValues(changesDataSet, "Subset values");

        // Insert code to reconcile errors. In this case, reject changes.
        foreach(DataTable changesTable in changesDataSet.Tables)
        {
            if (changesTable.HasErrors)
            {
                foreach(DataRow changesRow in changesTable.Rows)
                {
                    //Console.WriteLine(changesRow["Item"]);
                    if((int)changesRow["Item",DataRowVersion.Current ]> 100)
                    {
                        changesRow.RejectChanges();
                        changesRow.ClearErrors();
                    }
                }
            }
        }
        // Add a column to the changesDataSet.
        changesDataSet.Tables["Items"].Columns.Add(
            new DataColumn("newColumn"));
        PrintValues(changesDataSet, "Reconciled subset values");
        // Merge changes back to first DataSet.
        dataSet.Merge(changesDataSet, false,
            System.Data.MissingSchemaAction.Add);
    }
    PrintValues(dataSet, "Merged Values");
}

private void Row_Changed(object sender, DataRowChangeEventArgs e)
{
    Console.WriteLine("Row Changed " + e.Action.ToString()
        + "\table" + e.Row.ItemArray[0]);
}

private void PrintValues(DataSet dataSet, string label)
{
    Console.WriteLine(label + "\n");
    foreach(DataTable table in dataSet.Tables)
    {
        Console.WriteLine("TableName: " + table.TableName);
        foreach(DataRow row in table.Rows)
        {
            foreach(DataColumn column in table.Columns)
            {
                Console.Write("\table " + row[column] );
            }
            Console.WriteLine();
        }
    }
}

Private Sub DemonstrateMerge()
    ' Create a DataSet with one table, two columns, 
    ' and three rows.
    Dim dataSet As New DataSet("dataSet")
    Dim table As New DataTable("Items")
    Dim idColumn As New DataColumn("id", _
        Type.GetType("System.Int32"), "")
    idColumn.AutoIncrement = True
    Dim itemColumn As New DataColumn("Item", _
        Type.GetType("System.Int32"), "")

    ' Create DataColumn array to set primary key.
    Dim keyColumn(0) As DataColumn
    Dim row As DataRow

    ' Create variable for temporary DataSet. 
    Dim changesDataSet As DataSet

    ' Add RowChanged event handler for the table.
    AddHandler table.RowChanged, AddressOf Row_Changed
    dataSet.Tables.Add(table)
    table.Columns.Add(idColumn)
    table.Columns.Add(itemColumn)

    ' Set primary key column.
    keyColumn(0) = idColumn
    table.PrimaryKey = keyColumn

    ' Add ten rows.
    Dim i As Integer
    For i = 0 To 9
        row = table.NewRow()
        row("Item") = i
        table.Rows.Add(row)
    Next i

    ' Accept changes.
    dataSet.AcceptChanges()
    PrintValues(dataSet, "Original values")

    ' Change row values.
    table.Rows(0)("Item") = 50
    table.Rows(1)("Item") = 111

    ' Add one row.
    row = table.NewRow()
    row("Item") = 74
    table.Rows.Add(row)

    ' Insert code for error checking. Set one row in error.
    table.Rows(1).RowError = "over 100"
    PrintValues(dataSet, "Modified and New Values")

    ' If the table has changes or errors, create a subset DataSet.
    If dataSet.HasChanges(DataRowState.Modified Or DataRowState.Added) _
        And dataSet.HasErrors Then
        ' Use GetChanges to extract subset.
        changesDataSet = dataSet.GetChanges( _
            DataRowState.Modified Or DataRowState.Added)
        PrintValues(changesDataSet, "Subset values")

        ' Insert code to reconcile errors. In this case, reject changes.
        Dim changesTable As DataTable
        For Each changesTable In  changesDataSet.Tables
            If changesTable.HasErrors Then
                Dim changesRow As DataRow
                For Each changesRow In  changesTable.Rows
                    'Console.WriteLine(changesRow["Item"]);
                    If CInt(changesRow("Item", _
                        DataRowVersion.Current)) > 100 Then
                        changesRow.RejectChanges()
                        changesRow.ClearErrors()
                    End If
                Next changesRow
            End If
        Next changesTable

        ' Add a column to the changesDataSet.
        changesDataSet.Tables("Items").Columns.Add( _
            New DataColumn("newColumn"))
        PrintValues(changesDataSet, "Reconciled subset values")

        ' Merge changes back to first DataSet.
        dataSet.Merge(changesDataSet, False, _
            System.Data.MissingSchemaAction.Add)
    End If
    PrintValues(dataSet, "Merged Values")
End Sub
        
 Private Sub Row_Changed(sender As Object, e As DataRowChangeEventArgs)
     Console.WriteLine("Row Changed " + e.Action.ToString() _
        + ControlChars.Tab + e.Row.ItemArray(0).ToString())
 End Sub
    
Private Sub PrintValues(dataSet As DataSet, label As String)
     Console.WriteLine(label + ControlChars.Cr)
     Dim table As DataTable
     For Each table In  dataSet.Tables
         Console.WriteLine("TableName: " + table.TableName)
         Dim row As DataRow
         For Each row In  table.Rows
             Dim column As DataColumn
             For Each column In  table.Columns
                 Console.Write(ControlChars.Tab & " " _
                    & row(column).ToString())
             Next column
             Console.WriteLine()
         Next row
     Next table
End Sub

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• ForeignKeyConstraint
• UniqueConstraint
• Using DataSets in ADO.NET

Merge(DataRow[], Boolean, MissingSchemaAction)

Source:

DataSet.cs

Merges an array of DataRow objects into the current DataSet, preserving or discarding changes in the DataSet and handling an incompatible schema according to the given arguments.

public:
 void Merge(cli::array <System::Data::DataRow ^> ^ rows, bool preserveChanges, System::Data::MissingSchemaAction missingSchemaAction);

public void Merge (System.Data.DataRow[] rows, bool preserveChanges, System.Data.MissingSchemaAction missingSchemaAction);

member this.Merge : System.Data.DataRow[] * bool * System.Data.MissingSchemaAction -> unit

Public Sub Merge (rows As DataRow(), preserveChanges As Boolean, missingSchemaAction As MissingSchemaAction)

Parameters

rows

DataRow[]

The array of DataRow objects to be merged into the DataSet.

preserveChanges

Boolean

true to preserve changes in the DataSet; otherwise, false.

missingSchemaAction

MissingSchemaAction

One of the MissingSchemaAction values.

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

To facilitate explanation of the Merge method, we use "target" to signify the current DataSet, and "source" to name the second (parameter) DataSet. The target DataSet is so named because it is the object upon which an action (the merge) occurs. The second DataSet is called a "source" because the information it contains does not change, but instead is merged into the current DataSet.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• Using DataSets in ADO.NET

Merge(DataSet, Boolean, MissingSchemaAction)

Source:

DataSet.cs

Merges a specified DataSet and its schema with the current DataSet, preserving or discarding changes in the current DataSet and handling an incompatible schema according to the given arguments.

public:
 void Merge(System::Data::DataSet ^ dataSet, bool preserveChanges, System::Data::MissingSchemaAction missingSchemaAction);

public void Merge (System.Data.DataSet dataSet, bool preserveChanges, System.Data.MissingSchemaAction missingSchemaAction);

member this.Merge : System.Data.DataSet * bool * System.Data.MissingSchemaAction -> unit

Public Sub Merge (dataSet As DataSet, preserveChanges As Boolean, missingSchemaAction As MissingSchemaAction)

Parameters

dataSet

DataSet

The DataSet whose data and schema will be merged.

preserveChanges

Boolean

true to preserve changes in the current DataSet; otherwise, false.

missingSchemaAction

MissingSchemaAction

One of the MissingSchemaAction values.

Exceptions

ArgumentNullException

The dataSet is null.

Examples

The following example creates a simple DataSet with one table, two columns, and ten rows. Two values are changed, and one row is added. A subset of the changed data is created using the GetChanges method. After reconciling errors, a new column is added to the subset, changing the schema. When the Merge method is called with the missingSchemaAction set to MissingSchemaAction.Add, the new column is added to the original DataSet object's schema.

private void DemonstrateMergeMissingSchema()
{
    // Create a DataSet with one table, two columns,
    // and three rows.
    DataSet dataSet = new DataSet("dataSet");
    DataTable table = new DataTable("Items");
    DataColumn idColumn = new DataColumn("id",
        Type.GetType("System.Int32"));
    idColumn.AutoIncrement=true;
    DataColumn itemColumn = new DataColumn("Item",
        Type.GetType("System.Int32"));
    // DataColumn array to set primary key.

    DataColumn[] keyColumn= new DataColumn[1];
    DataRow row;
    // Create variable for temporary DataSet.
    DataSet changeDataSet;

    // Add RowChanged event handler for the table.
    table.RowChanged+= new DataRowChangeEventHandler(
        Row_Changed);
    dataSet.Tables.Add(table);
    table.Columns.Add(idColumn);
    table.Columns.Add(itemColumn);

    // Set primary key column.
    keyColumn[0]= idColumn;
    table.PrimaryKey=keyColumn;

    // Add ten rows.
    for(int i = 0; i <10;i++)
    {
        row=table.NewRow();
        row["Item"]= i;
        table.Rows.Add(row);
    }

    // Accept changes.
    dataSet.AcceptChanges();
    PrintValues(dataSet, "Original values");

    // Change row values.
    table.Rows[0]["Item"]= 50;
    table.Rows[1]["Item"]= 111;

    // Add one row.
    row=table.NewRow();
    row["Item"]=74;
    table.Rows.Add(row);

    // Insert code for error checking. Set one row in error.
    table.Rows[1].RowError= "over 100";
    PrintValues(dataSet, "Modified and New Values");
    // If the table has changes or errors, create a subset DataSet.
    if(dataSet.HasChanges(DataRowState.Modified |
        DataRowState.Added)& dataSet.HasErrors)
    {
        // Use GetChanges to extract subset.
        changeDataSet = dataSet.GetChanges(
            DataRowState.Modified|DataRowState.Added);
        PrintValues(changeDataSet, "Subset values");

        // Insert code to reconcile errors. Reject the changes.
        foreach(DataTable changeTable in changeDataSet.Tables)
        {
            if (changeTable.HasErrors)
            {
                foreach(DataRow changeRow in changeTable.Rows)
                {
                    //Console.WriteLine(changeRow["Item"]);
                    if((int)changeRow["Item",
                        DataRowVersion.Current ]> 100)
                    {
                        changeRow.RejectChanges();
                        changeRow.ClearErrors();
                    }
                }
            }
        }
        // Add a column to the changeDataSet to change the schema.
        changeDataSet.Tables["Items"].Columns.Add(
            new DataColumn("newColumn"));
        PrintValues(changeDataSet, "Reconciled subset values");

        // Add values to the rows for each column.
        foreach(DataRow rowItem in changeDataSet.Tables["Items"].Rows)
        {
            rowItem["newColumn"] = "my new schema value";
        }
        // Merge changes back to first DataSet.
        dataSet.Merge(changeDataSet, false,
            System.Data.MissingSchemaAction.Add);
    }
    PrintValues(dataSet, "Merged Values");
}

private void Row_Changed(object sender, DataRowChangeEventArgs e)
{
    Console.WriteLine("Row Changed " + e.Action.ToString()
        + "\table" + e.Row.ItemArray[0]);
}

private void PrintValues(DataSet dataSet, string label)
{
    Console.WriteLine("\n" + label);
    foreach(DataTable table in dataSet.Tables)
    {
        Console.WriteLine("TableName: " + table.TableName);
        foreach(DataRow row in table.Rows)
        {
            foreach(DataColumn column in table.Columns)
            {
                Console.Write("\table " + row[column] );
            }
            Console.WriteLine();
        }
    }
}

Private Sub DemonstrateMergeMissingSchema()
    ' Create a DataSet with one table, two columns, 
    ' and three rows.
    Dim dataSet As New DataSet("dataSet")
    Dim table As New DataTable("Items")
    Dim idColumn As New DataColumn("id", _
        Type.GetType("System.Int32"))
    idColumn.AutoIncrement = True
    Dim itemColumn As New DataColumn("Item", _
        Type.GetType("System.Int32"))

    ' DataColumn array to set primary key.
    Dim keyColumn(0) As DataColumn
    Dim row As DataRow

    ' Create variable for temporary DataSet. 
    Dim changeDataSet As DataSet

    ' Add RowChanged event handler for the table.
    AddHandler table.RowChanged, AddressOf Row_Changed
    dataSet.Tables.Add(table)
    table.Columns.Add(idColumn)
    table.Columns.Add(itemColumn)

    ' Set primary key column.
    keyColumn(0) = idColumn
    table.PrimaryKey = keyColumn

    ' Add ten rows.
    Dim i As Integer
    For i = 0 To 9
        row = table.NewRow()
        row("Item") = i
        table.Rows.Add(row)
    Next i

    ' Accept changes.
    dataSet.AcceptChanges()
    PrintValues(dataSet, "Original values")

    ' Change row values.
    table.Rows(0)("Item") = 50
    table.Rows(1)("Item") = 111

    ' Add one row.
    row = table.NewRow()
    row("Item") = 74
    table.Rows.Add(row)

    ' Insert code for error checking. Set one row in error.
    table.Rows(1).RowError = "over 100"
    PrintValues(dataSet, "Modified and New Values")
    ' If the table has changes or errors, 
    ' create a subset DataSet.
    If dataSet.HasChanges(DataRowState.Modified Or DataRowState.Added) _
        And dataSet.HasErrors Then
        ' Use GetChanges to extract subset.
        changeDataSet = dataSet.GetChanges(DataRowState.Modified _
            Or DataRowState.Added)
        PrintValues(changeDataSet, "Subset values")
        ' Insert code to reconcile errors. In this case, reject changes.
        Dim changeTable As DataTable
        For Each changeTable In  changeDataSet.Tables
            If changeTable.HasErrors Then
                Dim changeRow As DataRow
                For Each changeRow In  changeTable.Rows
                    If CInt(changeRow("Item", _
                        DataRowVersion.Current)) > 100 Then
                        changeRow.RejectChanges()
                        changeRow.ClearErrors()
                    End If
                Next changeRow
            End If
        Next changeTable

        ' Add a column to the changeDataSet to change the schema.
        changeDataSet.Tables("Items").Columns.Add( _
            New DataColumn("newColumn"))
        PrintValues(changeDataSet, "Reconciled subset values")

        ' Add values to the rows for each column.
        Dim rowItem As DataRow
        For Each rowItem In  changeDataSet.Tables("Items").Rows
            rowItem("newColumn") = "my new schema value"
        Next rowItem

        ' Merge changes back to first DataSet.
        dataSet.Merge(changeDataSet, False, _
            System.Data.MissingSchemaAction.Add)
    End If
    PrintValues(dataSet, "Merged Values")
End Sub
    
Private Sub Row_Changed(sender As Object, _
    e As DataRowChangeEventArgs)
     Console.WriteLine("Row Changed " & e.Action.ToString() _
        & ControlChars.Tab & e.Row.ItemArray(0).ToString())
End Sub
 
Private Sub PrintValues(dataSet As DataSet, label As String)
    Console.WriteLine(ControlChars.Cr & label)
    Dim table As DataTable
    For Each table In  dataSet.Tables
        Console.WriteLine("TableName: " & table.TableName)
        Dim row As DataRow
        For Each row In  table.Rows
            Dim column As DataColumn
            For Each column In  table.Columns
                Console.Write(ControlChars.Tab & " " _
                    & row(column).ToString())
            Next column
            Console.WriteLine()
        Next row
    Next table
End Sub

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

In a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

To facilitate explanation of the Merge method, we use "target" to signify the current DataSet, and "source" to name the second (parameter) DataSet. The target DataSet is so named because it is the object upon which an action (the merge) occurs. The second DataSet is called a "source" because the information it contains does not change, but instead is merged into the current DataSet.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• Using DataSets in ADO.NET

Merge(DataTable, Boolean, MissingSchemaAction)

Source:

DataSet.cs

Merges a specified DataTable and its schema into the current DataSet, preserving or discarding changes in the DataSet and handling an incompatible schema according to the given arguments.

public:
 void Merge(System::Data::DataTable ^ table, bool preserveChanges, System::Data::MissingSchemaAction missingSchemaAction);

public void Merge (System.Data.DataTable table, bool preserveChanges, System.Data.MissingSchemaAction missingSchemaAction);

member this.Merge : System.Data.DataTable * bool * System.Data.MissingSchemaAction -> unit

Public Sub Merge (table As DataTable, preserveChanges As Boolean, missingSchemaAction As MissingSchemaAction)

Parameters

table

DataTable

The DataTable whose data and schema will be merged.

preserveChanges

Boolean

One of the MissingSchemaAction values.

missingSchemaAction

MissingSchemaAction

true to preserve changes in the DataSet; otherwise, false.

Exceptions

ArgumentNullException

The dataSet is null.

Examples

The following example creates a simple DataSet with one table, two columns, and ten rows. A second DataTable is created that is nearly identical to the first except that a new DataColumn is added to the table. Two rows are added to the second table, which is then merged into the DataSet with the preserveChanges argument set to false, and the missingSchemaAction argument set to MissingSchemaAction.Add.

private void DemonstrateMergeTableAddSchema()
{
    // Create a DataSet with one table, two columns, and ten rows.
    DataSet dataSet = new DataSet("dataSet");
    DataTable table = new DataTable("Items");

    // Add table to the DataSet
    dataSet.Tables.Add(table);

    // Create and add two columns to the DataTable
    DataColumn idColumn = new DataColumn("id",
        Type.GetType("System.Int32"),"");
    idColumn.AutoIncrement=true;
    DataColumn itemColumn = new DataColumn("Item",
        Type.GetType("System.Int32"),"");
    table.Columns.Add(idColumn);
    table.Columns.Add(itemColumn);

    // Set the primary key to the first column.
    table.PrimaryKey = new DataColumn[1]{ idColumn };

    // Add RowChanged event handler for the table.
    table.RowChanged+= new DataRowChangeEventHandler(Row_Changed);

    // Add ten rows.
    for(int i = 0; i <10;i++)
    {
        DataRow row=table.NewRow();
        row["Item"]= i;
        table.Rows.Add(row);
    }

    // Accept changes.
    dataSet.AcceptChanges();
    PrintValues(dataSet, "Original values");

    // Create a second DataTable identical to the first, with
    // one extra column using the Clone method.
    DataTable cloneTable = table.Clone();
    cloneTable.Columns.Add("extra", typeof(string));

    // Add two rows. Note that the id column can'table be the
    // same as existing rows in the DataSet table.
    DataRow newRow;
    newRow=cloneTable.NewRow();
    newRow["id"]= 12;
    newRow["Item"]=555;
    newRow["extra"]= "extra Column 1";
    cloneTable.Rows.Add(newRow);

    newRow=cloneTable.NewRow();
    newRow["id"]= 13;
    newRow["Item"]=665;
    newRow["extra"]= "extra Column 2";
    cloneTable.Rows.Add(newRow);

    // Merge the table into the DataSet.
    Console.WriteLine("Merging");
    dataSet.Merge(cloneTable,false,MissingSchemaAction.Add);
    PrintValues(dataSet, "Merged With Table, Schema Added");
}

private void Row_Changed(object sender,
    DataRowChangeEventArgs e)
{
    Console.WriteLine("Row Changed " + e.Action.ToString()
        + "\table" + e.Row.ItemArray[0]);
}

private void PrintValues(DataSet dataSet, string label)
{
    Console.WriteLine("\n" + label);
    foreach(DataTable table in dataSet.Tables)
    {
        Console.WriteLine("TableName: " + table.TableName);
        foreach(DataRow row in table.Rows)
        {
            foreach(DataColumn column in table.Columns)
            {
                Console.Write("\table " + row[column] );
            }
            Console.WriteLine();
        }
    }
}

Private Sub DemonstrateMergeTableAddSchema()
    ' Create a DataSet with one table, two columns, 
    'and ten rows.
    Dim dataSet As New DataSet("dataSet")
    Dim table As New DataTable("Items")

    ' Add tables to the DataSet
    dataSet.Tables.Add(table)

    ' Create and add two columns to the DataTable
    Dim idColumn As New DataColumn("id", _
        Type.GetType("System.Int32"), "")
    idColumn.AutoIncrement = True
    Dim itemColumn As New DataColumn("Item", _
        Type.GetType("System.Int32"), "")
    table.Columns.Add(idColumn)
    table.Columns.Add(itemColumn)

    ' DataColumn array to set primary key.
    Dim keyCol(0) As DataColumn

    ' Set primary key column.
    keyCol(0) = idColumn
    table.PrimaryKey = keyCol

    ' Add RowChanged event handler for the table.
    AddHandler table.RowChanged, AddressOf Row_Changed

    ' Add ten rows.
    Dim i As Integer
    Dim row As DataRow

    For i = 0 To 9
        row = table.NewRow()
        row("Item") = i
        table.Rows.Add(row)
    Next i

    ' Accept changes.
    dataSet.AcceptChanges()
    PrintValues(dataSet, "Original values")

    ' Create a second DataTable identical to the first
    ' with one extra column using the Clone method.
    Dim cloneTable As New DataTable
    cloneTable = table.Clone()

    ' Add column.
    cloneTable.Columns.Add("extra", _
        Type.GetType("System.String"))

    ' Add two rows. Note that the id column can't be the 
    ' same as existing rows in the DataSet table.
    Dim newRow As DataRow
    newRow = cloneTable.NewRow()
    newRow("id") = 12
    newRow("Item") = 555
    newRow("extra") = "extra Column 1"
    cloneTable.Rows.Add(newRow)
        
    newRow = cloneTable.NewRow()
    newRow("id") = 13
    newRow("Item") = 665
    newRow("extra") = "extra Column 2"
    cloneTable.Rows.Add(newRow)

    ' Merge the table into the DataSet.
    Console.WriteLine("Merging")
    dataSet.Merge(cloneTable, False, MissingSchemaAction.Add)
    PrintValues(dataSet, "Merged With Table, Schema Added")
End Sub
  
Private Sub Row_Changed(sender As Object, _
    e As DataRowChangeEventArgs)
    Console.WriteLine("Row Changed " & e.Action.ToString() _
        & ControlChars.Tab & e.Row.ItemArray(0).ToString())
End Sub
    
Private Sub PrintValues(dataSet As DataSet, label As String)
    Console.WriteLine(ControlChars.Cr & label)
    Dim table As DataTable
    Dim row As DataRow
    Dim column As DataColumn
    For Each table In  dataSet.Tables
        Console.WriteLine("TableName: " & table.TableName)
        For Each row In  table.Rows             
            For Each column In  table.Columns
                Console.Write(ControlChars.Tab & " " _
                    & row(column).ToString())
            Next column
            Console.WriteLine()
        Next row
    Next table
 End Sub

Remarks

The Merge method is used to merge two DataSet objects that have largely similar schemas. A merge is typically used on a client application to incorporate the latest changes from a data source into an existing DataSet. This allows the client application to have a refreshed DataSet with the latest data from the data source.

The Merge method is typically called at the end of a series of procedures that involve validating changes, reconciling errors, updating the data source with the changes, and finally refreshing the existing DataSet.

iOn a client application, it is common to have a single button that the user can click that gathers the changed data and validates it before sending it back to a middle-tier component. In this scenario, the GetChanges method is first invoked. That method returns a second DataSet optimized for validating and merging. This second DataSet object contains only the DataTable and DataRow objects that were changed, resulting in a subset of the original DataSet. This subset is generally smaller, and thus more efficiently passed back to a middle-tier component. The middle-tier component then updates the original data source with the changes through stored procedures. The middle tier can then send back either a new DataSet that includes original data and the latest data from the data source (by running the original query again), or it can send back the subset with any changes that have been made to it from the data source. (For example, if the data source automatically creates unique primary key values, these values can be propagated back to the client application.) In either case, the returned DataSet can be merged back into the client application's original DataSet with the Merge method.

When the Merge method is called, the schemas of the two DataSet objects are compared because it is possible that the schemas may have been changed. For example, in a business-to-business scenario, new columns may have been added to an XML schema by an automated process. If the source DataSet contains schema elements (added DataColumn objects) that are missing in the target, the schema elements can be added to the target by setting the missingSchemaAction argument to MissingSchemaAction.Add. In that case, the merged DataSet contains the added schema and data.

After merging schemas, the data is merged.

When merging a new source DataSet into the target, any source rows with a DataRowState value of Unchanged, Modified, or Deleted are matched to target rows with the same primary key values. Source rows with a DataRowState value of Added are matched to new target rows with the same primary key values as the new source rows.

During a merge, constraints are disabled. If any constraints cannot be enabled at the end of merge, a ConstraintException is generated and the merged data is retained while the constraints are disabled. In this case, the EnforceConstraints property is set to false, and all rows that are invalid are marked in error. The errors must be resolved before attempting to reset the EnforceConstraints property to true.

See also

• Using DataSets in ADO.NET