Question

我很困惑如何做到这一点，因为我很陌生，通过c＃访问sql服务器。我想查询表测验，其中时间介于startTime和EndTime之间。但是，当我尝试添加时间参数时，它表示我有一个空引用异常。

DateTime date = DateTime.Now;

    SqlConnection con = new SqlConnection("Data Source=.\\SQLSERVER;Initial Catalog=quizMaker;Integrated Security=True");
    SqlCommand com;     

subjects = "Subject-3";



        con.Open();
        SqlParameter time = new SqlParameter("@time", SqlDbType.DateTime);
        time.Value = date;
        com.Parameters.Add(time); //error pops up here
        SqlParameter subjected = new SqlParameter("@subject", SqlDbType.VarChar, 20);
        subjected.Value = subjects;
        com = new SqlCommand("Select * from quiz where StartTime<=@time and EndTime>=@time and Subject_ID = @subject", con);


        com.ExecuteNonQuery();
        con.Close();

Answer 1

未分配Com，com为null。首先将参数添加到com，然后执行com = new SqlCommand

com.Parameters.Add(time); //<-- com = null
com = new SqlCommand("Select * from quiz where StartTime<=@time and EndTime>=@time and Subject_ID = @subject", con); //<-- com has a value (!= null)

只需要做其他明智的事情：放置

com = new SqlCommand("Select * from quiz where StartTime<=@time and EndTime>=@time and Subject_ID = @subject", con); //<-- com has a value (!= null)

在

com.Parameters.Add(time); //<-- com = null

System.NullReferenceException添加DateTime SQL参数

1 个答案: