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How to check username availability?

Hi Guys,
I'm using ASP.net + VB.Net + Access. Please help me to uderstand how to check username availability? Thanks. I have the following code:

Protected Sub submitButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles submitButton.Click
        Dim con As New Data.OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("..\App_data\GLC.mdb"))
        Dim SqlCommand As New Data.OleDb.OleDbCommand
        Dim SqlCommandPro As New Data.OleDb.OleDbCommand
        SqlCommand.CommandText = "INSERT INTO Students ( Username, [Password], SchoolID, LastName, FirstName, Email ) Values ('" + UserName.Text.Replace("'", "_") + "','" + Password.Text.Replace("'", "_") + "','" + DropDownListSchool.SelectedValue + "','" + LastName.Text.Replace("'", "_") + "','" + FirstName.Text.Replace("'", "_") + "','" + Email.Text.Replace("'", "_") + "')"
        SqlCommandPro.CommandText = "INSERT INTO ProgramsStudents (Username, CourseID) Values ('" + UserName.Text.Replace("'", "_") + "','" + DropDownListProgram.SelectedValue + "')"
 
 
 
        If Page.IsValid Then
 
 
            con.Open()
 
            SqlCommand.Connection = con
            SqlCommandPro.Connection = con
 
            SqlCommand.ExecuteNonQuery()
            SqlCommandPro.ExecuteNonQuery()
 
 
            con.Close()
 
        End If
    End Sub

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Robertyue
Asked:
Robertyue
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1 Solution
 
RobertyueAuthor Commented:
Plus, it says my insert statement is wrong...
0
 
RobertyueAuthor Commented:
My bad, the insert function works fine...But i need to know how to check username availability, thanks
0
 
GreymanMSCCommented:
Check the tables before attempting to update.
Protected Sub submitButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles submitButton.Click
    If Page.IsValid Then
       Dim con As New Data.OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("..\App_data\GLC.mdb"))
 
        'check if name is in table
        Dim sqlCheckStudent As String = "SELECT UserName FROM Students WHERE UserName='" + UserName.Text.Replace("'", "_") + "')"
 
        'insert data into table
        Dim sqlInsertStudent As String = "INSERT INTO Students ( Username, Password, SchoolID, LastName, FirstName, Email ) Values ('" + UserName.Text.Replace("'", "_") + "','" + Password.Text.Replace("'", "_") + "','" + DropDownListSchool.SelectedValue + "','" + LastName.Text.Replace("'", "_") + "','" + FirstName.Text.Replace("'", "_") + "','" + Email.Text.Replace("'", "_") + "')"
 
        'check if courseid is in table for that student
        Dim sqlCheckCourse As String = "SELECT CourseID FROM ProgramsStudents WHERE Username='" + UserName.Text.Replace("'", "_") + "' AND CourseID='" + DropDownListProgram.SelectedValue + "'"
 
        Dim sqlInsertCourse As String = "INSERT INTO ProgramsStudents (Username, CourseID) Values ('" + UserName.Text.Replace("'", "_") + "','" + DropDownListProgram.SelectedValue + "')"
 
        con.Open()
        Dim okayToContinue As Boolean = False
        Dim doCheckStudent As New Data.OleDb.OleDbCommand(sqlCheckStudent, con)
        If IsDBNull(doCheckStudent.ExecuteScalar) Then
            Dim doInsertStudent As New Data.OleDb.OleDbCommand(sqlCheckStudent, con)
            okayToContinue = (0 < doInsertStudent.ExecuteNonQuery())
        Else
            '----------------------------------------
            'The Username is already in the table.
            'Do something here.
            '----------------------------------------
            okayToContinue = False 'or true, depending on the above
        End If
        If okayToContinue Then
            Dim doCheckCourse As New Data.OleDb.OleDbCommand(sqlCheckCourse, con)
            If IsDBNull(doCheckCourse.ExecuteScalar) Then
                Dim doInsertCourse As New Data.OleDb.OleDbCommand(sqlInsertCourse, con)
                doInsertCourse.ExecuteNonQuery()
            End If
        End If
        con.close
    End If
End Sub

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RobertyueAuthor Commented:
What's okayToContinue for? If the Username is already exist, you cannot insert any data. On the other side, if the username is not in the database, you should be able to excute both insert command. I'm really confued with okayToContinue. Could you please explain a liitle? Thanks
0
 
RobertyueAuthor Commented:
No matter what username (not exist in the databse) I entered, it says the user is already exist. Please see my code
 Protected Sub submitButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles submitButton.Click
        Dim con As New Data.OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("..\App_data\GLC.mdb"))
        Dim SqlCommand As New Data.OleDb.OleDbCommand
        Dim SqlCommandPro As New Data.OleDb.OleDbCommand
        Dim sqlCheckStudent As String = "SELECT UserName FROM Students WHERE UserName='" + UserName.Text.Replace("'", "_") + "'"
        SqlCommand.CommandText = "INSERT INTO Students ( Username, [Password], SchoolID, LastName, FirstName, Email ) Values ('" + UserName.Text.Replace("'", "_") + "','" + Password.Text.Replace("'", "_") + "','" + DropDownListSchool.SelectedValue + "','" + LastName.Text.Replace("'", "_") + "','" + FirstName.Text.Replace("'", "_") + "','" + Email.Text.Replace("'", "_") + "')"
        SqlCommandPro.CommandText = "INSERT INTO ProgramsStudents (Username, CourseID) Values ('" + UserName.Text.Replace("'", "_") + "','" + DropDownListProgram.SelectedValue + "')"
 
 
 
        If Page.IsValid Then
            Try
 
 
                con.Open()
 
                Dim okayToContinue As Boolean = False
                Dim doCheckStudent As New Data.OleDb.OleDbCommand(sqlCheckStudent, con)
 
                If IsDBNull(doCheckStudent.ExecuteScalar) Then
 
                    SqlCommand.Connection = con
                    SqlCommandPro.Connection = con
 
                    SqlCommand.ExecuteNonQuery()
                    SqlCommandPro.ExecuteNonQuery()
                Else
                    ErrorMessage2.Text = "The Username is already exist!"
                End If
 
            Catch
                ErrorMessage.Text = "Error retrieving data, please try again later!"
            Finally
                con.Close()
            End Try
        Else
            ErrorMessage.Text = "Please complete everything!"
 
        End If
    End Sub

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RobertyueAuthor Commented:
I figured out. Thank you anyway!
Protected Sub submitButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles submitButton.Click
       
 
 
        Dim con As New Data.OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("..\App_data\GLC.mdb"))
        Dim Counter As String = "SELECT COUNT(Username) FROM STUDENTS WHERE Username=@Username"
 
 
        Dim SqlCommand As String = "INSERT INTO Students ( Username, [Password], SchoolID, LastName, FirstName, Email ) Values (@Username,@Password,@SchoolID,@LastName,@FirstName,@Email)"
        Dim SqlCommandPro As String = "INSERT INTO ProgramsStudents (Username, CourseID) Values (@Username,@CourseID)"
 
 
 
        If Page.IsValid Then
 
 
            con.Open()
            Dim Count As New Data.OleDb.OleDbCommand(Counter, con)
            Count.Parameters.AddWithValue("@Username", UserName.Text)
 
            Dim CountValue As Integer
            CountValue = CInt(Count.ExecuteScalar())
 
            Dim Mycommand As New Data.OleDb.OleDbCommand(SqlCommand, con)
            Dim Mycommandd As New Data.OleDb.OleDbCommand(SqlCommandPro, con)
 
            Mycommand.Parameters.AddWithValue("@Username", UserName.Text.Replace("'", "_"))
            Mycommand.Parameters.AddWithValue("@Password", Password.Text.Replace("'", "_"))
            Mycommand.Parameters.AddWithValue("@SchoolID", DropDownListSchool.SelectedValue)
            Mycommand.Parameters.AddWithValue("@LastName", LastName.Text.Replace("'", "_"))
            Mycommand.Parameters.AddWithValue("@FirstName", FirstName.Text.Replace("'", "_"))
            Mycommand.Parameters.AddWithValue("@Email", Email.Text.Replace("'", "_"))
 
            Mycommandd.Parameters.AddWithValue("@Username", UserName.Text.Replace("'", "_"))
            Mycommandd.Parameters.AddWithValue("@CourseID", DropDownListProgram.SelectedValue)
 
 
            If CountValue = 0 Then
                Mycommand.ExecuteNonQuery()
                Mycommandd.ExecuteNonQuery()
 
 
            Else : ErrorMessage2.Text = "User Name is Already Exist!"
            End If
            con.Close()
 
 
        End If
 
    End Sub

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