I cannot get the output parameter when use function import by Entity Framework

问题

Here's my SQL Server stored procedure :

ALTER PROCEDURE [dbo].[SearchUser]
  (@Text NVARCHAR(100),  
   @TotalRows INT = 0 OUTPUT)   
AS
BEGIN 
   SELECT @TotalRows=1000
   SELECT * from Users
END

And my C# code

using (var context = new TestDBEntities())
{
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32));
    context.SearchUser("", outputParameter);
    Response.Write(outputParameter.Value);
}

However outputParameter.Value always is null.

Could anybody tell me why?

回答1:

Output parameters filled by its actual values during the execution of the stored procedure.

But table-valued stored procedure actually get executed only in moment when you're trying to iterate resulting recordset, but not calling a wrapper method.

So, this DOES'T work:

using (var context = new TestDBEntities()) 
{ 
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32)); 
    context.SearchUser("", outputParameter); 

    // Paremeter value is null, because the stored procedure haven't been executed
    Response.Write(outputParameter.Value); 

}

This DOES:

using (var context = new TestDBEntities()) 
{ 
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32)); 

    // Procedure does not executes here, we just receive a reference to the output parameter
    var results = context.SearchUser("", outputParameter);

    // Forcing procedure execution
    results.ToList();

    // Parameter has it's actual value
    Response.Write(outputParameter.Value); 

}

When you're working with stored procedures what don't return any recordset, they execute immediately after a method call, so you have actual value in output parameter.

回答2:

We had a simular issue due to defered excecution our unit tests failed. In short if you have a stored proc that does NOT return anything you need to be sure to set the response type as 'None' when set as 'None' it will be excecuted when called and not defered.

In case you return anything (E.g. Scalar type of String results) it will excecute it when you use the result even if that .Count() or .ToList() is outside of the method that contains the function call.

So try not to force excecution if not need, when needed it should excecute but be sure to declare it correctly or it might not work.

回答3:

I have same problem before. The main reason I think that the entities framework has the bug in case the user stored procedure has output parameter and return a result set. For example:

ALTER PROCEDURE [dbo].[SearchTest]
(   
    @RowTotal   INT = 0 OUTPUT,
    @RowCount   INT = 0 OUTPUT
)
AS
BEGIN   
    SET NOCOUNT ON
    SELECT * FROM SomeThing 
    SELECT @RowTotal = 1233, @RowCount = 5343
END

However if you change the user stored procedure as following, you can get the output params

ALTER PROCEDURE [dbo].[SearchTest]
(   
    @RowTotal   INT = 0 OUTPUT,
    @RowCount   INT = 0 OUTPUT
)
AS
BEGIN   
    SET NOCOUNT ON  
    SELECT @RowTotal = 1233, @RowCount = 5343
END

You can workaround as following:

ALTER PROCEDURE [dbo].[SearchTest]
AS
BEGIN   
    DECLARE @RowTotal INT, @RowCount INT

    SET NOCOUNT ON  
    SELECT @RowTotal = 1233, @RowCount = 5343

    SELECT @RowTotal  AS RowTotal, @RowCount AS RowCount, s.*
    FROM SomeThing s

END

If anybody has better solution, please tell me

来源：https://stackoverflow.com/questions/5881359/i-cannot-get-the-output-parameter-when-use-function-import-by-entity-framework

标签

stored-procedures

linq-to-entities