如何使用 DataSet 和 DataAdapter C#/asp.net 进行删除？

Question

How can I delete a row from Database using DataSet and DataAdapter (I'm not allowed to SqlCommand)>

Table has four columns

UserId(auto-generated) | UserName | Age | Salary

I tried the code below but it throws NUll Exception when i click Button3_Click(Delete Button)

System.NullReferenceException: 'Object reference not set to an instance of an object.' System.Data.DataRowCollection.Find(...) returned null.

    string s = 
    ConfigurationManager.ConnectionStrings["student"].ConnectionString;
      protected void Page_Load(object sender, EventArgs e)
        {
           using (SqlConnection con = new SqlConnection(s))
         {
            string query = "select * from student";
            using (SqlDataAdapter da = new SqlDataAdapter(query,con))
            {
                DataSet ds = new DataSet();
                da.Fill(ds);
                ds.Tables[0].PrimaryKey = new DataColumn[] { 
                ds.Tables[0].Columns["UserName"] };
                ViewState["query"] = query;
                ViewState["dataset"] = ds;
            }
        }
    }




 protected void Button3_Click(object sender, EventArgs e)
    {
        using (SqlConnection con = new SqlConnection(s))
        {
            using (SqlDataAdapter da = new 

             SqlDataAdapter((string)ViewState["query"],con))
            {

                DataSet ds = (DataSet)ViewState["dataset"];

                ds.Tables[0].Rows.Find("'" + TextBox2.Text + "'").Delete();
                SqlCommandBuilder com = new SqlCommandBuilder(da);
                da.Update(ds);


            }
        }
    }

Answer 1

I'm pretty sure that UserId is the primary-key of your DataTable. So you can use DataRowCollection.Find (if no key is defined you get a MissingPrimaryKeyException ). But of course you need to specify the UserId and not the UserName . Otherwise Find returns null which causes your exception. Your screenshot shows that you are passing the UserName

Instead of Find you can use LINQ:

DataRow rowToDelete =  ds.Tables[0].AsEnumerable()
   .FirstOrDefault(r => r.Field<string>("UserName") == TextBox2.Text.Trim());
if(rowToDelete != null) 
{
    rowToDelete.Delete();
    // ...
}