如何在.NET中使用SQL用户定义的函数？

Question

我在DB中创建了一个标量函数

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[fn_GetUserId_Username]
    (
    @Username varchar(32)
    )
RETURNS int
AS
    BEGIN
    DECLARE @UserId int
    SELECT @UserId = UserId FROM [User] WHERE Username = @Username
    RETURN @UserId
    END

现在我想在.NET C#或VB.NET代码中运行它.

我使用Entity Framework,我试图用功能映射映射它,但我没有成功.我不关心用简单的DbCommand来做,问题是我没有得到任何结果(该函数存在于Entities类中):

public int GetUserIdByUsername(string username)
{
    EntityConnection connection = (EntityConnection)Connection;            
    DbCommand com = connection.StoreConnection.CreateCommand();
    com.CommandText = "fn_GetUserId_Username";
    com.CommandType = CommandType.StoredProcedure;
    com.Parameters.Add(new SqlParameter("Username", username));
    if (com.Connection.State == ConnectionState.Closed) com.Connection.Open();
    try
    {
        var result = com.ExecuteScalar(); //always null
    }
    catch (Exception e)
    { 
    }
    return result;
}

有什么解决方案吗？C#或VB.NET中的帖子都会受到欢迎.

Answer 1

在这种情况下,听起来正确的方法是使用实​​体框架的功能来定义.NET函数并将其映射到UDF,但我想我明白为什么在使用ADO时没有得到预期的结果.NET要做到这一点 - 你告诉它你正在调用一个存储过程,但你真的在调用一个函数.

试试这个:

public int GetUserIdByUsername(string username)
{
    EntityConnection connection = (EntityConnection)Connection;            
    DbCommand com = connection.StoreConnection.CreateCommand();
    com.CommandText = "select dbo.fn_GetUserId_Username(@Username)";
    com.CommandType = CommandType.Text;
    com.Parameters.Add(new SqlParameter("@Username", username));
    if (com.Connection.State == ConnectionState.Closed) com.Connection.Open();
    try
    {
        var result = com.ExecuteScalar(); // should properly get your value
        return (int)result;
    }
    catch (Exception e)
    {
        // either put some exception-handling code here or remove the catch 
        //   block and let the exception bubble out 
    }
}