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DataSet.Merge Method (DataTable)

.NET Framework 1.1

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

[Visual Basic]
Overloads Public Sub Merge( _
   ByVal table As DataTable _
)
[C#]
public void Merge(
 DataTable table
);
[C++]
public: void Merge(
 DataTable* table
);
[JScript]
public function Merge(
   table : DataTable
);

Parameters

table
The DataTable whose data and schema will be merged.

Exceptions

Exception Type Condition
ArgumentNullException The dataSet is a null reference (Nothing in Visual Basic).

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 usual 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 will then update 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 will contain 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.

Example

[Visual Basic, C#, C++] 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.

[Visual Basic] 
Private Sub DemonstrateMergeTable()
    ' Create a DataSet with one table, two columns, and ten rows.
    Dim ds As New DataSet("myDataSet")
    Dim t As New DataTable("Items")

    ' Add tables to the DataSet
    ds.Tables.Add(t)

    ' Add columns
    Dim c1 As New DataColumn("id", Type.GetType("System.Int32"), "")
    Dim c2 As New DataColumn("Item", Type.GetType("System.Int32"), "")
    t.Columns.Add(c1)
    t.Columns.Add(c2)

    ' DataColumn array to set primary key.
    Dim keyCol(1) As DataColumn

    ' Set primary key column.
    keyCol(0) = c1
    t.PrimaryKey = keyCol

    ' Add RowChanged event handler for the table.
    AddHandler t.RowChanged, AddressOf Row_Changed

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

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

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

    ' Create a second DataTable identical to the first.
    Dim t2 As DataTable
    t2 = t.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")
    ds.Merge(t2)
    PrintValues(ds, "Merged With Table")
End Sub 'DemonstrateMergeTable
    
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 'Row_Changed

Private Sub PrintValues(ds As DataSet, label As String)
    Console.WriteLine(ControlChars.Cr + label)
    Dim t As DataTable
    Dim r As DataRow
    Dim c As DataColumn
    For Each t In  ds.Tables
        Console.WriteLine("TableName: " + t.TableName) 
        For Each r In  t.Rows             
            For Each c In  t.Columns
                Console.Write(ControlChars.Tab + " " + r(c).ToString())
            Next c
            Console.WriteLine()
        Next r
    Next t
End Sub

[C#] 
private void DemonstrateMergeTable(){
   // Create a DataSet with one table, two columns, and ten rows.
   DataSet ds = new DataSet("myDataSet");
   DataTable t = new DataTable("Items");

   // Add table to the DataSet
   ds.Tables.Add(t);

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

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

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

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

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

   PrintValues(ds, "Original values");

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

   // Add three rows. Note that the id column can't 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");
   ds.Merge(t2);
   PrintValues(ds, "Merged With table.");

}

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

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

[C++] 
private:
 void DemonstrateMergeTable(){
    // Create a DataSet with one table, two columns, and ten rows.
    DataSet* ds = new DataSet(S"myDataSet");
    DataTable* t = new DataTable(S"Items");

    // Add table to the DataSet
    ds->Tables->Add(t);

    // Add columns
    DataColumn* c1 = new DataColumn(S"id", Type::GetType(S"System.Int32"),S"");
    DataColumn* c2 = new DataColumn(S"Item", Type::GetType(S"System.Int32"),S"");
    t->Columns->Add(c1);
    t->Columns->Add(c2);

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

    // Set primary key column.
    keyCol[0]= c1;
    t->PrimaryKey=keyCol;

    // Add a RowChanged event handler for the table.
    t->RowChanged += new DataRowChangeEventHandler(this, &Form1::Row_Changed);

    // Add ten rows.
    for(int i = 0; i <10;i++){
       DataRow* r=t->NewRow();
       r->Item[S"id"] = __box(i);
       r->Item[S"Item"]= __box(i);
       t->Rows->Add(r);
    }
    // Accept changes.
    ds->AcceptChanges();

    PrintValues(ds, S"Original values");

    // Create a second DataTable identical to the first.
    DataTable* t2 = t->Clone();

    // Add three rows. Note that the id column can't be the
    // same as existing rows in the DataSet table.
    DataRow* newRow;
    newRow = t2->NewRow();
    newRow->Item[S"id"] = __box(14);
    newRow->Item[S"item"] = __box(774);

    //Note the alternative method for adding rows.

    Object* temp0 [] = {__box(12), __box(555)};
    t2->Rows->Add(temp0);

    Object* temp1 [] = {__box(13), __box(665)};
    t2->Rows->Add(temp1);

    // Merge the table into the DataSet
    Console::WriteLine(S"Merging");
    ds->Merge(t2);
    PrintValues(ds, S"Merged With table.");

 }
 
 void Row_Changed(Object* /*sender*/, DataRowChangeEventArgs* e){
    Console::WriteLine(S"Row Changed {0}\t{1}", __box(e->Action), e->Row->ItemArray[0]);
 }
 
 void PrintValues(DataSet* ds, String* label){
    Console::WriteLine(S"\n{0}", label);
    System::Collections::IEnumerator* myEnum = ds->Tables->GetEnumerator();
    while (myEnum->MoveNext())
    {
       DataTable* t = __try_cast<DataTable*>(myEnum->Current);
       Console::WriteLine(S"TableName: {0}", t->TableName);
       System::Collections::IEnumerator* myEnum1 = t->Rows->GetEnumerator();
       while (myEnum1->MoveNext())
       {
          DataRow* r = __try_cast<DataRow*>(myEnum1->Current);
          System::Collections::IEnumerator* myEnum2 = t->Columns->GetEnumerator();
          while (myEnum2->MoveNext())
          {
             DataColumn* c = __try_cast<DataColumn*>(myEnum2->Current);
             Console::Write(S"\t {0}", r->Item[c] );
          }
          Console::WriteLine();
       }
    }
 }

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

DataSet Class | DataSet Members | System.Data Namespace | DataSet.Merge Overload List | DataTable

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