Using SqlTransaction in C#, how to get an output parameter from a stored procedure and insert into another table?

Question

I have two tables: Table1 and Table2. I need newly inserted Id (from Table1 ) as an output parameter which should be inserted into Table2 . And I must use SqlTransaction or TransactionScope here.

Stored procedure:

    CREATE PROC InsertTable1
    (
        @Name nvarchar(50),
        @OutputParam int out
    )
    AS
    BEGIN
        INSERT INTO Table1(Name) 
        VALUES(@Name)

        SELECT @OutputParam = SCOPE_IDENTITY() 
    END

C# code:

SqlTransaction transaction = db.sqlconn.BeginTransaction();

SqlParameter[] param = new SqlParameter[2];
param[0] = new SqlParameter("@Name", "TestName");
param[1] = new SqlParameter("@OutputParam", SqlDbType.Int);
param[1].Direction = ParameterDirection.Output;

SqlHelper.ExecuteNonQuery(transaction, "InsertTable1", param);

int outputId = (int)param[1].Value;

When I run and debug the project I get an error

Object reference not set to an instance of an object

just after execution of

int outputId = (int)param[1].Value;

I think the transaction is closing the connection or something. It works if I don't use transaction. But I have to use transaction anyhow. I am open to any alternative ways to achieve the same result.

Answer 1

For problems concerning transactions take a look TransactionScope class. Here is the intro part from microsoft documentation .

The TransactionScope class provides a simple way to mark a block of code as participating in a transaction, without requiring you to interact with the transaction itself. A transaction scope can select and manage the ambient transaction automatically. Due to its ease of use and efficiency, it is recommended that you use the TransactionScope class when developing a transaction application.

Also you have transaction properties ( TransactionInformation and Current ) at your disposal to investigate status of transaction while debugging. This is all I can think of right now that wasn't suggested already.

Answer 2

First off, the overload of SqlHelper.ExecuteNonQuery you are using takes an array of parameter values , not an array of SqlParameter . It only compiles and runs because the type is object . So it will derive its own parameters via a SqlCommandBuilder and try to set the values on them from your param argument, but of course a SqlParameter cannot have a SqlParameter as its .Value . The point is moot however, because the comments on the source code (below) specifically say you have no access to OUTPUT or RETURN values from this method.

    /// <summary>
    /// Execute a stored procedure via a SqlCommand (that returns no resultset) against the specified 
    /// SqlTransaction using the provided parameter values.  This method will query the database to discover the parameters for the 
    /// stored procedure (the first time each stored procedure is called), and assign the values based on parameter order.
    /// </summary>
    /// <remarks>
    /// This method provides no access to output parameters or the stored procedure's return value parameter.
    /// 
    /// e.g.:  
    ///  int result = ExecuteNonQuery(conn, trans, "PublishOrders", 24, 36);
    /// </remarks>
    /// <param name="transaction">a valid SqlTransaction</param>
    /// <param name="spName">the name of the stored procedure</param>
    /// <param name="parameterValues">an array of objects to be assigned as the input values of the stored procedure</param>
    /// <returns>an int representing the number of rows affected by the command</returns>
    public static int ExecuteNonQuery(SqlTransaction transaction, string spName, params object[] parameterValues)
    {
        //if we receive parameter values, we need to figure out where they go
        if ((parameterValues != null) && (parameterValues.Length > 0))
        {
            //pull the parameters for this stored procedure from the parameter cache (or discover them & populate the cache)
            SqlParameter[] commandParameters = SqlHelperParameterCache.GetSpParameterSet(transaction.Connection.ConnectionString, spName);

            //assign the provided values to these parameters based on parameter order
            AssignParameterValues(commandParameters, parameterValues);

            //call the overload that takes an array of SqlParameters
            return ExecuteNonQuery(transaction, CommandType.StoredProcedure, spName, commandParameters);
        }
        //otherwise we can just call the SP without params
        else
        {
            return ExecuteNonQuery(transaction, CommandType.StoredProcedure, spName);
        }
    }

Answer 3

USE OUTPUT clause to get inserted data and save into a temporary table.

Return that data from stored procedure

Answer 4

您不需要在输出中获取值，如果您想在另一个表中插入数据，在存储过程中，您可以轻松编写另一个插入查询，将这个 id 插入另一个表中

Answer 5

我可以看到您正在使用自定义 SqlHelper.ExecuteNonQuery 方法来执行查询，能否请您分享 SqlHelper.ExecuteNonQuery 方法