Recipe 6.4 Using ADO.NET and SQL Server DBMS Transactions Together

Problem

You need to use a DBMS transaction within a SQL Server stored procedure from an ADO.NET transaction with the SQL Server .NET data provider.

Solution

Use error-checking within a catch block as shown in Example 6-5.

The sample uses a single stored procedure:

InsertCategories_Transacted

Used to insert a single record into the Categories table in the Northwind database within a DBMS transaction. If the record insert fails, the transaction is rolled back; otherwise, the transaction is committed.

The sample code contains two event handlers:

Form.Load

Sets up the sample by filling a DataTable with the Categories table from the Northwind sample database. The default view of the table is bound to a data grid on the form.

Insert Button.Click

Inserts user-entered data for the Categories records into the Northwind database within a manual transaction using a DBMS transacted stored procedure. The transaction is rolled back in the stored procedure if either the Force DBMS Rollback checkbox is checked or if no value is entered for the Category Name field. Otherwise, the ADO.NET manual transaction is committed.

Example 6-5. Stored procedure: InsertCategories_Transacted

CREATE PROCEDURE InsertCategories_Transacted
    @CategoryId int output,
    @CategoryName nvarchar(15),
    @Description ntext,
    @Rollback bit = 0
AS
    SET NOCOUNT ON
    
    begin tran
    
    insert Categories(
        CategoryName,
        Description)
    values (
        @CategoryName,
        @Description)
    
    if @@error<>0 or @@rowcount=0 or @Rollback=1
    begin
        rollback tran
        set @CategoryID = -1
        return 1
    end

    commit tran
    
    set @CategoryID = Scope_Identity( )

    select @CategoryID CategoryId

    return 0

The C# code is shown in Example 6-6.

Example 6-6. File: DbmsTransactionForm.cs

// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient;

private SqlDataAdapter da;
private DataTable dt;

//  . . . 

private void DbmsTransactionForm_Load(object sender, System.EventArgs e)
{
    // Fill the table.
    String sqlText = "SELECT CategoryID, CategoryName, Description " +
        "FROM Categories";
    da = new SqlDataAdapter(sqlText,
        ConfigurationSettings.AppSettings["Sql_ConnectString"]);
    dt = new DataTable("Categories");
    da.FillSchema(dt, SchemaType.Source);
    da.Fill(dt);

    // Bind the default view of the table to the grid.
    dataGrid.DataSource = dt.DefaultView;
}

private void insertButton_Click(object sender, System.EventArgs e)
{
    // Create the connection.
    SqlConnection conn = new SqlConnection(
        ConfigurationSettings.AppSettings["Sql_ConnectString"]);
    // Create the transaction.
    conn.Open( );
    SqlTransaction tran = conn.BeginTransaction( );

    // Create command in the transaction with parameters.
    SqlCommand cmd =
        new SqlCommand("InsertCategories_Transacted", conn, tran);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.Add("@CategoryID", SqlDbType.Int).Direction =
        ParameterDirection.Output;
    cmd.Parameters.Add("@CategoryName", SqlDbType.NVarChar, 15);
    cmd.Parameters.Add("@Description", SqlDbType.NText);
    cmd.Parameters.Add("@Rollback", SqlDbType.Bit);

    try
    {
        // Set the parameters to the user-entered values.
        // Set the CategoryName to DBNull if not entered.
        if(categoryNameTextBox.Text.Trim( ).Length == 0)
            cmd.Parameters["@CategoryName"].Value = DBNull.Value;
        else
            cmd.Parameters["@CategoryName"].Value =
                categoryNameTextBox.Text;
        cmd.Parameters["@Description"].Value = descriptionTextBox.Text;
        cmd.Parameters["@Rollback"].Value =
            forceDbmsRollbackCheckBox.Checked ? 1 : 0;

        // Attempt to insert the record.
        cmd.ExecuteNonQuery( );

        // Success. Commit the transaction.
        tran.Commit( );
        MessageBox.Show("Transaction committed.");
    }
    catch (SqlException ex)
    {
        bool spRollback = false;
        foreach (SqlError err in ex.Errors)
        {
            // Check if transaction rolled back in the
            // stored procedure.
            if(err.Number == 266)
            {
                MessageBox.Show(ex.Message,
                    "DBMS transaction rolled back in " +
                    "stored procedure",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                spRollback = true;
                break;
            }
        }
        if (!spRollback)
        {
            // transaction was not rolled back by the DBMS
            // SqlException error. Roll back the transaction.
            tran.Rollback( );
            MessageBox.Show(ex.Message);
        }
    }
    catch (Exception ex)
    {
        // Other Exception. Roll back the transaction.
        tran.Rollback( );
        MessageBox.Show(ex.Message);
    }
    finally
    {
        conn.Close( );
    }

    // Refresh the data.
    da.Fill(dt);
}

Discussion

SQL Server returns error 266 if a stored procedure exits with a transaction count that is not the same as when the stored procedure was entered. The count is returned by the function @@TRANCOUNT. The error simply sends a message to the client and does not affect execution of the stored procedure. It doesn't mean that the DBMS transaction in the stored procedure could not be started, completed, or terminated properly.

When calling a stored procedure from a .NET manual transaction, the transaction count entering the stored procedure is 1. Using the SQL BEGIN TRAN command in the stored procedure creates a nested transaction, increasing the transaction count to 2. If the stored procedure transaction is subsequently committed with the COMMIT TRAN command, the transaction count is decremented back to 1. Keep in mind commits of inner transactions don't free resources or make modifications permanent, and don't affect outer transactions. If ROLLBACK is called, all inner transactions to the outermost transaction are rolled back and the transaction count is decremented to 0. Error 266 is returned by the rolled back stored procedure since the transaction count entering the stored procedure is 1 while the count when exiting is 0. Attempting to commit or roll back the transaction from .NET after it has been rolled back in the stored procedure will cause an InvalidOperationException because the transaction has already been rolled back.

The solution catches exceptions raised while executing a stored procedure and checks if they correspond to SQL Server error 266, which is the mismatch between the starting and exiting stored procedure transaction count values as a result of the stored procedure rolling back the transaction. If the stored procedure has rolled back the transaction, it is not rolled back by the .NET code. All other errors raised while executing the stored procedure are rolled back by the .NET code.