How to close the sqldatareader within Using statement? - sql

Question

I'd like to use this code to verify if duplication occurs or not before saving the data to the database. How am I supposed to close the sqldatareader? (As what the error shows me)
con.ConnectionString = "Data Source=PC85AAIEw\SQLEXPRESS;Initial Catalog=Student;Integrated Security=True"
cmd.Connection = con
con.Open()
Dim theQuery As String = "SELECT * FROM Profile WHERE RollNo=#RollNo AND Name=#Name"
Dim cmd1 As SqlCommand = New SqlCommand(theQuery, con)
cmd1.Parameters.AddWithValue("#RollNo", TextBox1.Text)
cmd1.Parameters.AddWithValue("#Name", TextBox2.Text)
Using reader As SqlDataReader = cmd1.ExecuteReader()
If reader.HasRows Then
MessageBox.Show("User already registered! Please try again.", "Error", MessageBoxButtons.OK)
Else
cmd.CommandText = "INSERT INTO Profile VALUES ('" & rollno & "' , '" & name & "' , '" & gender & "' , '" & address & "' , '" & phoneno & "' , '" & datereg & "' , '" & faculty & "' , '" & course & "' , '" & semester & "')"
MessageBox.Show("Profile has been successfully registered!", "Thank you", MessageBoxButtons.OK)
i = cmd.ExecuteNonQuery()
End If
End Using
con.Close()

Answer 1

The error are referring to is because you must complete the execution of the data reader before you try to execute another command on the same connection.
Additionally there are some issues with your code:
It is strongly recommended you use and then dispose of SqlConnections as you use them, do not try to reuse these globally in your application. The ado.net SQL Server client library will handle connection pooling for you by default.
You need to use parameters with your insert just like you did on your select.
Do not to use AddWithValue when adding your parameters, instead use the constructor and also specify the sql data type. If RollNo is a number (like integer) then you should pass the value as an integer to your parameter. I assumed it was a string stored in a varchar.
Wrap all types that implement IDisposable in Using statements to ensure resources are always released. (In case any one wants to nitpick, no it is not required for SqlCommand in this case.)
Dim recordExists As Boolean
Using con As SqlConnection = New SqlConnection("Data Source=PC85AAIEw\SQLEXPRESS;Initial Catalog=Student;Integrated Security=True")
Using cmd As SqlCommand = New SqlCommand("SELECT RollNo FROM Profile WHERE RollNo=#RollNo AND Name=#Name", con)
cmd.Parameters.Add("#RollNo", SqlDbType.VarChar).Value = TextBox1.Text
cmd.Parameters.Add("#Name", SqlDbType.VarChar).Value = TextBox2.Text
con.Open()
Using reader As SqlDataReader = cmd.ExecuteReader()
recordExists = reader.HasRows
End Using
End Using
End Using
If recordExists Then
MessageBox.Show("User already registered! Please try again.", "Error", MessageBoxButtons.OK)
Else
Using con As SqlConnection = New SqlConnection("Data Source=PC85AAIEw\SQLEXPRESS;Initial Catalog=Student;Integrated Security=True")
Using cmd As SqlCommand = New SqlCommand("INSERT INTO Profile (RollNo, Name) VALUES (#RollNo, #Name)", con)
cmd.Parameters.Add("#RollNo", SqlDbType.VarChar).Value = TextBox1.Text
cmd.Parameters.Add("#Name", SqlDbType.VarChar).Value = TextBox2.Text
con.Open()
cmd.ExecuteNonQuery()
MessageBox.Show("Profile has been successfully registered!", "Thank you", MessageBoxButtons.OK)
End Using
End Using
End If

Answer 2

if you are using using then not need to close. because it internally close all connection. The code would be like this
using(var con=new Sqlconnection("Data Source=PC85AAIEw\SQLEXPRESS;Initial Catalog=Student;Integrated Security=True")){
cmd.Connection = con
con.Open()
Dim theQuery As String = "SELECT * FROM Profile WHERE RollNo=#RollNo AND Name=#Name"
Dim cmd1 As SqlCommand = New SqlCommand(theQuery, con)
cmd1.Parameters.AddWithValue("#RollNo", TextBox1.Text)
cmd1.Parameters.AddWithValue("#Name", TextBox2.Text)
Using reader As SqlDataReader = cmd1.ExecuteReader()
If reader.HasRows Then
MessageBox.Show("User already registered! Please try again.", "Error", MessageBoxButtons.OK)
Else
cmd.CommandText = "INSERT INTO Profile VALUES ('" & rollno & "' , '" & name & "' , '" & gender & "' , '" & address & "' , '" & phoneno & "' , '" & datereg & "' , '" & faculty & "' , '" & course & "' , '" & semester & "')"
MessageBox.Show("Profile has been successfully registered!", "Thank you", MessageBoxButtons.OK)
i = cmd.ExecuteNonQuery()
End If
End Using
con.Close()}