When i click the save button error shows Index or Primary Key cannot contain a Null Value.

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Database Design as follows

Column Data Type
ID Text (Primary Key)
Faculty Code text
course Code text

design as follows;

Id Combobox
Faculty Code Combo box
Course Code Combo box

New Save Clear (Buttons)

New button code as follows;

C#

private void Btn_New_Click(object sender, EventArgs e)
        {
            GFun.BindAccessConn();
            OleDbCommand cmd = new OleDbCommand("select MAX(ID) +1 from Tb_Faculty_Approval", GFun.OleDbCon);
            OleDbDataReader oledr = cmd.ExecuteReader();
            while (oledr.Read())
            {
                cb_id.Text = oledr[0].ToString().Trim();
            }

        }

The ID is the auto increment for that i written a code in the new button.

In database i set ID as Primary key.

In the run mode i click the new button the ID 1 will appear.
In faculty Code select the faculty
In the Course Code Select the couse

Then when i click the Save Button the error shows as follows;

Index or Primary Key cannot contain  a Null Value.

what is the problem in the New Button code.

Or in the database design in the ID column want to change?

please help me.

Thanks & Regards,
Narasiman P.

Posted 19-Feb-13 19:44pm

Member 8054539

Updated 19-Feb-13 19:51pm

Dee_Bee

v3

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Rockstar_ 20-Feb-13 1:54am

To work this code, at least one record should be there in database.

2 solutions

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uspatel · Answer 1 · 2013-02-19T19:49:00

Solution 1

The better way to auto increment ise set identity to the column.
use this query to alter your column

alter table table1 add col3 int identity(1,1)

Now you do not need to insert this value.Each time new row inserted,ID column incremented by 1.

Try it.

Posted 19-Feb-13 19:49pm

uspatel

Hemant Singh Rautela · Answer 2 · 2013-02-19T19:59:00

You can use it...

C#

public double maxid(string tablename)
      {
          double number = 0; ;
          SqlDataAdapter da = new SqlDataAdapter("select max(id) from " + tablename + " ", con);
          SqlDataAdapter da2 = new SqlDataAdapter("select * from " + tablename + " ", con);
          DataSet ds = new DataSet();
          DataSet ds2 = new DataSet();
          da.Fill(ds, tablename);
          da2.Fill(ds2, tablename);
          double num = ds2.Tables[0].Rows.Count;
          if (num.ToString() == "0")
          {
              number = 0;
          }
          else
          {
              number = Convert.ToDouble(ds.Tables[0].Rows[0][0]);
          }
          return (number);
      }

or you can check if max(id) is dbnull then return 0....with only select max(id) from tablename

thanks
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