DataAdapter is not adding "auto increment" fields

  • Thread starter Thread starter Dmitry Sazonov
  • Start date Start date
D

Dmitry Sazonov

Please, somebody help me. DataAdapter is not adding fields to tables with
"auto increment" ID :-( :-(

I have 2 related tables, let say, table "Orders" and table "OrderDetails"
--------------------------------
| Orders
| - - - - - - - - - - - - - - -
| ID int, autoincrement, primary key
| ...
--------------------------------

--------------------------------
| OrderDetails
| - - - - - - - - - - - - - - -
| OrderID int, (related to field ID in table Orders)
| ...
--------------------------------

// ------- Now, I create DataRow for orders and adding it to DataSet:

OrdersRow order = ds.Orders.NewOrdersRow();
order.Name = ...; // etc, set all properties
ds.AddOrdersRow( order );

// --- at this moment "order.ID" have some value, let say 1000

// ------- then I'm creating order details

OrderDetailsRow od = ds.Orders.NewOrderDetailsRow();
od.OrderID = order.ID;
ds.AddOrderDetailsRow( od );

// --- everything is still good

// -------- now I'm commiting changes:

OrdersAdapter.Update( ds.Orders ); // --- it worked fine.
// But my new order added to database with different ID, let say 1002.
// It could be any number, even 1000, in this case there will be
no error.
// But it could be more than 1000 and I get the error
//
// Database remember last ID and adds record with this number.
// at this moment, in memory object "ds.Orders" contains different
information
// from data source

// if I will try to add OrderDetails to database,
OrderDetailsAdapter.Update( ds.OrderDetails ); // --- exeption !!!

I will get error "You cannot add or change a record because a related record
is requred in table 'Orders' "
 
Are you setting the Unique property of the specific data column or do you
mean the autoincrment is at the db level? If not, set it
dataTable.Columns("ID").Unique = true
 
Dmitry,

This is a common topic/scenario on the newsgroup. Here's a
response that usually helps developers handle the scenario using
ADO.NET.

I hope this information proves helpful.

David Sceppa
Microsoft
This posting is provided "AS IS" with no warranties,
and confers no rights. You assume all risk for your use.
© 2004 Microsoft Corporation. All rights reserved.



This is a fairly common scenario that ADO.NET handles much
better than any of its predecessors. It may seem complex at
first, but once you've handled the scenario once, it will
hopefully feel more intuitive.


1.) How do I keep pending parent and children in synch?

Set the ADO.NET DataColumn's AutoIncrement property to True
and ADO.NET will generate placeholder values for new rows. The
new values depend on the AutoIncrementStep, AutoIncrementSeed,
and the last value used in the DataTable. I recommend setting
AutoIncrementSeed and AutoIncrementStep to -1. These settings
will generate placeholder values of -1, -2, -3, … There are two
benefits to this approach. The values won't conflict with any
that actually exist in the database. The user will not
misinterpret the placeholder value as an actual value from the
database.

As you add the parent rows and ADO.NET generates placeholder
values, use those placeholder values for your pending child rows.
The DataRelation object will make it easy to go from parent to
child and back, either in code or in bound controls.


2.) How do I fetch the new key values for the parent rows as I
submit them?

If you're using SQL Server, this process is actually very
simple. If you were writing your own queries, you would execute
an "INSERT INTO…" query to insert the new row and then execute a
"SELECT SCOPE_IDENTITY()" query to retrieve the last identity
value generated on that connection.

The DataAdapter submits changes via its InsertCommand
property. You can append ";SELECT @@IDENTITY AS MyIDColumn" to
the end of the "INSERT INTO..." query. (SQL 2000 users should
use "SELECT SCOPE_IDENTITY()..." instead of "SELECT @@IDENTITY".
See SQL Server Books OnLine for more information on why.) If
you're building your DataAdapters via Visual Studio .NET's
DataAdapter Configuration Wizard, the wizard will do this for you
automatically.

If you're writing your code by hand, make sure the
InsertCommand's UpdatedRowSource property is set to Both (the
default) or FirstReturnedRecord. This property controls whether
the DataAdapter will fetch the row returned by the query and
apply that data to the DataRow object.

This functionality is possible because SQL Server allows you
to execute a batch of queries that returns rows. However, not
all databases support this feature.

If you're working with an Access database, you'll need to go
a slightly different route. Trap for the DataAdapter's
RowUpdated event and use code to check for a successful insert.
Execute the "SELECT @@IDENTITY" query using a Command object and
assign the value returned by the query to the appropriate column
and call the DataRow object's AcceptChanges method. Your code
will look something like this:

Visual Basic .NET:
Dim da As New OleDbDataAdapter(strSQL, strConn)
Dim cn As OleDbConnection = da.SelectCommand.Connection
Dim cmdGetIdentity As New OleDbCommand("SELECT @@IDENTITY", cn)
AddHandler da.RowUpdated, AddressOf HandleRowUpdated
Dim tbl As DataTable = CreateMyDataTable()
da.Fill(tbl)
...
da.Update(tbl)

Private Sub HandleRowUpdated(ByVal sender As Object, _
ByVal e As
OleDbRowUpdatedEventArgs)
If e.Status = UpdateStatus.Continue AndAlso _
e.StatementType = StatementType.Insert Then
e.Row("OrderID") =
Int32.Parse(cmdGetIdentity.ExecuteScalar().ToString())
e.Row.AcceptChanges()
End If
End Sub

Visual C# .NET:
OleDbDataAdapter da = new OleDbDataAdapter(strSQL, strConn);
OleDbConnection cn = da.SelectCommand.Connection;
OleDbCommand cmdGetIdentity = new OleDbCommand("SELECT
@@IDENTITY", cn);
da.RowUpdated += new
OleDbRowUpdatedEventHandler(HandleRowUpdated);
DataTable tbl = CreateMyDataTable();
da.Fill(tbl);
...
da.Update(tbl);

private void HandleRowUpdated(object sender,
OleDbRowUpdatedEventArgs e)
{
if ((e.Status == UpdateStatus.Continue) &&
((e.StatementType == StatementType.Insert))
{
e.Row["OrderID"] =
Int32.Parse(cmdGetIdentity.ExecuteScalar().ToString());
e.Row.AcceptChanges();
}
}

You can use similar techniques to retrieve server-generated
values from other databases as well. MySQL developers can use
the "LAST_INSERT_ID()" instead of "@@IDENTITY" to retrieve the
last auto-increment value generated. Oracle developers can use
"SELECT SequenceName.CURRVAL FROM DUAL" to retrieve the last
value generated for a sequence on the connection.


3.) How do I cascade the new key values to the child rows before
I submit them?

This is the simplest part of the process. When you create a
DataRelation object, ADO.NET will add a ForeignKeyConstraint
object to make sure that child rows match up to a parent row.
The ForeignKeyConstraint object exposes a UpdateRule property.
If this property is set to Cascade (the default), ADO.NET will
automatically cascade changes made to the parent down to the
associated child rows.

So, if you have a DataRelation set up between the DataTables
based on the auto-increment column, and you've set the parent
DataAdapter's InsertCommand to fetch the new auto-increment
values from the database, ADO.NET will cascade the new values
down to the associated child rows automatically.


I hope this information proves helpful. For more
information, see Chapter 11 of Microsoft ADO.NET, available
through Microsoft Press.
 
Thank you very much!
It worked for Access databse and I sure it will for MS SQL and My SQL
databases...

Thank you again.
 
Dmitry,

No problem. I'm pleased to hear the information resolved
the problem.

David Sceppa
Microsoft
This posting is provided "AS IS" with no warranties,
and confers no rights. You assume all risk for your use.
© 2004 Microsoft Corporation. All rights reserved.
 
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