当Entity Framework使用函数导入时,我无法获取输出参数

Question

这是我的SQL Server存储过程:

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outputParameter.Value总是为空.

谁能告诉我为什么？

Answer 1

在执行存储过程期间,输出参数由其实际值填充.

但是,当您尝试迭代结果记录集但不调用包装器方法时,表值存储过程实际上只会执行.

所以,这个DOES'T工作:

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); 

} 

当您使用存储过程时不返回任何记录集时,它们会在方法调用后立即执行,因此您在输出参数中具有实际值.