c# - ExecuteScalar 调用抛出异常 "Object reference not set to an instance of an object"

Question

在单元测试中调试以下方法时出现以下错误

Object reference not set to an instance of an object

点击以下行时

result = (int)validateDatabase.ExecuteScalar();

方法是

    public static Boolean Validate(string argument1, string argument2)
    {            
        int result = -1;

        using (var connection = new SqlConnection("connection string"))
        {
            SqlCommand validateDatabase = new SqlCommand("PROCEDURE NAME", connection);
            validateDatabase.CommandType = System.Data.CommandType.StoredProcedure;
            validateDatabase.Parameters.Add("@PARAMETER1", System.Data.SqlDbType.NVarChar).Value = argument1;
            validateDatabase.Parameters.Add("@PARAMETER2", System.Data.SqlDbType.NVarChar).Value = argument2; 

            try
            {
                connection.Open();
                result = (int)validateDatabase.ExecuteScalar();
            }
            catch (SqlException exception) { Trace.WriteLine("exception.Message); }
            finally { connection.Close(); }
        }
        return (int)result == 0 ? true : false; 
    }

Answer 1

ExecuteScalar 根据 MSDN，如果结果集为 null，则返回 null。这意味着您的转换无效

请参阅此处获取文档 SqlCommand.ExecuteScalar

如果您希望该转换起作用，请将其更改为可为空的 int

result = (int?)validateDatabase.ExecuteScalar();