不允许从数据类型 sql_variant 隐式转换为 varchar

Question

I'm getting this error when calling a stored procedure from .NET Entity Framework using Dapper.

Implicit conversion from data type sql_variant to varchar is not allowed.

The stored procedure parameter is @Name nvarchar(50) = NULL .

So ideally, it should accept a null value. When I call the stored procedure and pass @Name = null from .NET, I get gives this error.

This is the stored procedure:

CREATE PROCEDURE [dbo].[Member_Add]
    @Id NVARCHAR(50)  = NULL,
    @Name NVARCHAR(50)  = NULL
AS
BEGIN
    INSERT INTO [dbo].Member (Id, Name)
    VALUES (@Id, @Name)
END

Answer 1

Dapper was internally mapping object to sql_variant . When I pass null it was considering it as object type. As my stored procedure was expecting varchar , sql_variant was not convertible to it.

I started passing string.Empty instead of null object and it was working fine.

@Name = Request.Name??string.Empty;

Answer 2

对我来说，问题是我使用 Visual Studio 的“选择性粘贴”->“将 JSON 粘贴为类”自动生成了我的 DTO 类，并且它将某些成员的数据类型设置为对象而不是字符串。