Question

i have created that table on my sql server :

create table Empolyee(
ESSN int not null,
EFirstName varchar(20) not null ,
ELastName varchar(20) not null,
EJob varchar(20),
EBDate date,
ESalary int,

primary key(ESSN));

and in C# i try to add data to database using that code :

SqlConnection sqc = new SqlConnection("Data Source=.\\;Initial Catalog=DB;Integrated Security=True");
SqlDataAdapter da = new SqlDataAdapter();
DataSet ds = new DataSet();

        da.SelectCommand = new SqlCommand("INSERT INTO Empolyee VALUES (@ESSN,@EFirstName,@ELastName,@EJob,@EBDate,@ESalary)", sqc);
        da.SelectCommand.Parameters.Add("@ESSN", SqlDbType.Int).Value = textBox1.Text;
        da.SelectCommand.Parameters.Add("@EFirstName", SqlDbType.VarChar).Value = textBox2.Text;
        da.SelectCommand.Parameters.Add("@ELastName", SqlDbType.VarChar).Value = textBox3.Text;
        da.SelectCommand.Parameters.Add("@EJob", SqlDbType.VarChar).Value = textBox4.Text;
        da.SelectCommand.Parameters.Add("@EBDate", SqlDbType.Date).Value = maskedTextBox1.Text;
        da.SelectCommand.Parameters.Add("@ESalary", SqlDbType.Int).Value = textBox5.Text;

        // open connection
        sqc.Open();
        // excute the command
        da.InsertCommand.ExecuteNonQuery();
        // close connection
        sqc.Close();

i get that error when i run : Object reference not set to an instance of an object or System.NullReferenceException: Object reference not set to an instance of an object.

Answer 1

you haven’t assigned anything to da.InsertCommand – instead you have put an INSERT command into da.SelectCommand… just change all references from da.SelectCommand to da.InsertCommand in the code you show in your question:

    da.InsertCommand = new SqlCommand("INSERT INTO Empolyee VALUES (@ESSN,@EFirstName,@ELastName,@EJob,@EBDate,@ESalary)", sqc);
    da.InsertCommand.Parameters.Add("@ESSN", SqlDbType.Int).Value = textBox1.Text;
    da.InsertCommand.Parameters.Add("@EFirstName", SqlDbType.VarChar).Value = textBox2.Text;
    da.InsertCommand.Parameters.Add("@ELastName", SqlDbType.VarChar).Value = textBox3.Text;
    da.InsertCommand.Parameters.Add("@EJob", SqlDbType.VarChar).Value = textBox4.Text;
    da.InsertCommand.Parameters.Add("@EBDate", SqlDbType.Date).Value = maskedTextBox1.Text;
    da.InsertCommand.Parameters.Add("@ESalary", SqlDbType.Int).Value = textBox5.Text;

BTW you don’t need any SqlDataAdapter or DataSet to execute an INSERT – it can be done with SqlConnection and SqlCommand only.