使用实体框架导入功能时无法获取输出参数 [英] I cannot get the output parameter when use function import by Entity Framework

问题描述

这是我的SQL Server存储过程:

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

还有我的C#代码

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

但是outputParameter.Value始终为null.

However outputParameter.Value always is null.

有人可以告诉我为什么吗?

Could anybody tell me why?

推荐答案

在存储过程执行期间，输出参数由其实际值填充.

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

但是表值存储过程实际上仅在您尝试迭代结果记录集时才执行，而没有调用包装方法.

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.

所以，这行不通:

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); 

} 

这样做:

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); 

} 

在使用不返回任何记录集的存储过程时，它们将在方法调用后立即执行，因此您在输出参数中具有实际值.

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.

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