Copying Tables from One DataSet to Another

Solution Use one of the following techniques: • Use the Copy method of the DataTable when all of the data for a table needs to be copied.. • Use the Clone method of the DataTable t

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Recipe 5.2 Copying Tables from One DataSet to Another

Problem

You need to copy an existing schema and data from one DataSet to another

Solution

Use one of the following techniques:

• Use the Copy( ) method of the DataTable when all of the data for a table needs to

be copied

• Use the Clone( ) method of the DataTable to create the schema for each table in the destination DataSet when only a subset of the data needs to be copied You can use the ImportRows( ) method of the DataTable to copy the subset of rows from the source to the destination table

Once the destination tables are created and the data is copied into them, the example shows how to create the DataRelation objects from the source DataSet in the destination DataSet

The sample code contains two event handlers:

Form.Load

Sets up the sample by creating a DataSet containing the Orders and Order Details tables from Northwind and a relation between the two tables The default view for the Orders table is bound to a data grid on the form

Copy Button.Click

Creates a destination DataSet and copies the schema and specified data into it from the source DataSet created in the Form.Load event handler

The C# code is shown in Example 5-2

Example 5-2 File: CopyTablesBetweenDataSetsForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Data;

using System.Data.SqlClient;

// Table name constants

private const String ORDERS_TABLE = "Orders";

private const String ORDERDETAILS_TABLE = "OrderDetails";

// Relation name constants

private const String ORDERS_ORDERDETAILS_RELATION =

"Orders_OrderDetails_Relation";

// Field name constants

private const String ORDERID_FIELD = "OrderID";

private const String ORDERDATE_FIELD = "OrderDate";

private const String EMPLOYEEID_FIELD = "EmployeeID";

private DataSet dsSource;

//

private void CopyTablesBetweenDataSetsForm_Load(object sender,

System.EventArgs e)

{

dsSource = new DataSet("Source");

SqlDataAdapter da;

// Fill the Order table and add it to the DataSet

da = new SqlDataAdapter("SELECT * FROM Orders",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderTable = new DataTable(ORDERS_TABLE);

da.FillSchema(orderTable, SchemaType.Source);

da.Fill(orderTable);

dsSource.Tables.Add(orderTable);

// Fill the OrderDetails table and add it to the DataSet

da = new SqlDataAdapter("SELECT * FROM [Order Details]",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderDetailTable = new DataTable(ORDERDETAILS_TABLE); da.FillSchema(orderDetailTable, SchemaType.Source);

da.Fill(orderDetailTable);

dsSource.Tables.Add(orderDetailTable);

// Create a relation between the tables

dsSource.Relations.Add(ORDERS_ORDERDETAILS_RELATION,

dsSource.Tables[ORDERS_TABLE].Columns[ORDERID_FIELD],

dsSource.Tables[ORDERDETAILS_TABLE].Columns[ORDERID_FIELD], true);

// Bind the source and destination DataSet to the grids

sourceDataGrid.DataSource = dsSource.Tables[ORDERS_TABLE].DefaultView; }

private void copyButton_Click(object sender, System.EventArgs e)

{

// Create the destination DataSet into which to copy tables

DataSet dsDest = new DataSet("Destination");

if (copyAllRadioButton.Checked)

{

foreach(DataTable sourceTable in dsSource.Tables)

{

// First technique: when all rows need to be copied

dsDest.Tables.Add(sourceTable.Copy( ));

}

}

else if (copySubsetRadioButton.Checked)

{

int employeeId = 0;

try

{

employeeId = Convert.ToInt32(employeeIdTextBox.Text);

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

return;

}

// Second technique: can be used to import subset

foreach(DataTable dtSource in dsSource.Tables)

{

// Add logic to selectively copy tables

dsDest.Tables.Add(dtSource.Clone( ));

}

// Copy rows for selected employee from the Orders table

foreach(DataRow parentRow in

dsSource.Tables[ORDERS_TABLE].Select(

EMPLOYEEID_FIELD + "=" + employeeId))

{

dsDest.Tables[ORDERS_TABLE].ImportRow(parentRow);

// Copy the Order Details for the Order

foreach(DataRow childRow in

parentRow.GetChildRows(

ORDERS_ORDERDETAILS_RELATION))

{

dsDest.Tables[

ORDERDETAILS_TABLE].ImportRow(childRow);

}

}

}

// Create the relations in the destination DataSet

// Iterate over the collection of relations in the source

foreach(DataRelation sourceRelation in dsSource.Relations)

{

// Get the name of the parent and child table for the relation

String parentTableName = sourceRelation.ParentTable.TableName; String childTableName = sourceRelation.ChildTable.TableName;

// Get the number of parent columns for the source relation

int nCol = sourceRelation.ParentColumns.Length;

// Create an array of parent columns in the destination

DataColumn[] parentCols = new DataColumn[nCol];

for(int i = 0; i < nCol; i++)

parentCols[i] = dsDest.Tables[parentTableName].Columns[ sourceRelation.ParentColumns[i].Ordinal];

// Create an array of child columns in the destination

DataColumn[] childCols = new DataColumn[nCol];

for(int i = 0; i < nCol; i++)

childCols[i] = dsDest.Tables[childTableName].Columns[

sourceRelation.ChildColumns[i].Ordinal];

// Create the relation in the destination DataSet

dsDest.Relations.Add(

new DataRelation(sourceRelation.RelationName,

parentCols, childCols, false));

}

// Set the enforce constraints flag to match the source DataSet

dsDest.EnforceConstraints = dsSource.EnforceConstraints;

// Bind the default view of the Orders table to the grid

destDataGrid.DataSource = dsDest.Tables[ORDERS_TABLE].DefaultView;

}

Discussion

This sample demonstrates two scenarios for copying tables from one DataSet to another

In the first scenario, all of the data and tables in the source DataSet are copied to the destination This is accomplished by iterating over the collection of tables in the source DataSet and using the Copy( ) method of each DataTable object to copy both the schema and data for each table into the destination DataSet

In the second scenario, only a subset of the data in the source DataSet is copied to the destination Since there is a relation in place between the Orders and Order Details tables

in this case, only the child records related to the selected parent records are copied to the destination

Once the data has been copied, the DataRelation objects are copied by iterating over the collection of DataRelation objects in the source DataSet, and adding them to the

destination DataSet This involves creating an array of parent and source columns for the destination DataRelation from the parent and child column ordinals in the source

DataRelation This information, together with the name of the source DataRelation is used to create the DataRelation in the destination DataSet Finally, the

EnforceConstraints property in the destination DataRelation is set to match the source

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