Deny adding an already exist user

Question

User-2094959909 posted
Hello everyone,
I work with asp.net c# and i already worked with the code to add a new user and also go to login page to enter this user with username and password
My question is i want to do a test in addUser.aspx.cs that tests if this user i'm adding is already exists in the database the program show me a message "user already exists" but if not the program works normally ?
Can anyone help please

Answer 1

User-369506445 posted

Hi

Please follow below links

https://forums.asp.net/t/1589650.aspx?How+to+check+if+username+value+in+form+already+exists+in+DB+

https://www.aspsnippets.com/Articles/Check-whether-username-already-exists.aspx

http://msdn.microsoft.com/en-us/library/ms178329.aspx[^]

http://www.asp.net/web-forms/tutorials/security/membership/creating-user-accounts-cs[^]

http://geekswithblogs.net/dotNETvinz/archive/2009/04/30/creating-a-simple-registration-form-in-asp.net.aspx

Answer 2

User-1171043462 posted

Checking can be easily done within stored proc used for registration

WebForms: Simple User Registration Form Example in ASP.Net

MVC: Simple User Registration Form with Entity Framework Database

Also you can use jQuery AJAX to show whether Username is already Taken

Web Forms: Check UserName Availability in ASP.Net using jQuery

MVC: Check Username Availability (Exists) in Database using jQuery AJAX ...

Answer 3

User-2094959909 posted

public partial class AjouterConsulteur : System.Web.UI.Page
{
string strConnString = ConfigurationManager.ConnectionStrings["DBcon"].ConnectionString;
MySqlCommand com;
protected void Page_Load(object sender, EventArgs e)
{

}

protected void Button1_Click(object sender, EventArgs e)
{
MySqlConnection con = new MySqlConnection(strConnString);
//con.Open();
com = new MySqlCommand();
com.Connection = con;
com.CommandType = CommandType.Text;
com.Parameters.Clear();
com.Parameters.AddWithValue("@userid",TextBox1.Text);
com.Parameters.AddWithValue("@name", TextBox2.Text);
com.Parameters.AddWithValue("@username", TextBox3.Text);
com.Parameters.AddWithValue("@password", TextBox4.Text);
com.Parameters.AddWithValue("@role", TextBox5.Text);

com.CommandText = "insert into tblusers values (@userid,@name,@username,@password,@role)";
//com.CommandText = "insert into tblusers values ('99','99','99','99','99')";

//com.ExecuteNonQuery();
if (con.State == ConnectionState.Closed)
{
con.Open();
com.ExecuteNonQuery();
con.Close();
Label1.Text = "Successfully registered";
TextBox1.Text = "";
TextBox2.Text = "";
TextBox3.Text = "";
TextBox4.Text = "";
TextBox5.Text = "";

}

}
}

----------------

this is the code i use for adding a new user ... is there any solution i would try in just inside this code or not ?

thanks btw

Answer 4

User-369506445 posted

hi

if you <g class="gr_ gr_5 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling" id="5" data-gr-id="5">userid</g> is a primary key in your database when you <g class="gr_ gr_8 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar multiReplace" id="8" data-gr-id="8">are insert</g> a duplicate row you get <g class="gr_ gr_6 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins doubleReplace replaceWithoutSep" id="6" data-gr-id="6">error</g> and you'll understand this user already exists

please <g class="gr_ gr_7 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="7" data-gr-id="7">ry</g> below code :

SqlConnection con = new SqlConnection(strConnString);
            con.Open();
            string q = "insert into tblusers values (@userid,@name,@username,@password,@role)";
            var com = new SqlCommand(q,con);
            com.Connection = con;
            com.CommandType = CommandType.Text;
            com.Parameters.Clear();
            com.Parameters.AddWithValue("@userid", "1");
            com.Parameters.AddWithValue("@name", "vahid");
            com.Parameters.AddWithValue("@username", "vahidbakhtiary");
            com.Parameters.AddWithValue("@password", "vahidbakhtiary");
            com.Parameters.AddWithValue("@role", "1");

         
 
            try
            {
                com.ExecuteNonQuery();
            }
            catch (Exception exception)
            {
                if (exception.Message.Contains( @"Violation of PRIMARY KEY constraint"))
                {

                    // user already exists"
                   //here generate your message
                }
                
            }

Answer 5

User36583972 posted

Hi Omar27,

this is the code i use for adding a new user ... is there any solution i would try in just inside this code or not ?

You can just add a check detect the userid/name already exist in the database, then, give ocustomer a feedback.

protected void Button1_Click(object sender, EventArgs e)
        {
            MySqlConnection con = new MySqlConnection(strConnString);
            //con.Open();
            com = new MySqlCommand();
           if(CheckExistuser( "userId"))
            {
                return;
            }

            com.CommandText = "insert into tblusers values (@userid,@name,@username,@password,@role)";
            //com.CommandText = "insert into tblusers values ('99','99','99','99','99')";
            //com.ExecuteNonQuery();
            if (con.State == ConnectionState.Closed)
            {
                con.Open();
                com.ExecuteNonQuery();
                con.Close();
            }
        }

        public bool CheckExistuser(string userId)
        {
            bool result = false;
            try
            {
                //select the userid exist for this record
                com.CommandText = "SELECT userid, name FROM tblusers where userid= @userid";
                 //exist result = true;
            }
            catch
            {
                result = false;
            }

            return result;
        }

Best Regards,

Yong Lu

Answer 6

User-2094959909 posted
So i should put if (con.state == connectionState.closed){...........} inside try you added ??

Answer 7

User-369506445 posted

please try below code

public bool CheckExistuser(string userId)
        {
            bool result = false;
            try
            {
                string q = "SELECT count (1) FROM tblusers where userid= @userid";
                SqlConnection con = new SqlConnection(strConnString);
                var com = new SqlCommand(q, con);
                com.CommandType = CommandType.Text;
                com.Parameters.Clear();
                com.Parameters.AddWithValue("@userid", userId);
                if (con.State == ConnectionState.Closed)
                {
                    con.Open();
                    int count=(int) com.ExecuteScalar();
                    con.Close();
                    // if count be Equal 0 , doesn't Exist user , 
                    // if count be more than 0 , Exists user , 
                    if (count > 0)  
                        result= true;
                     
                }
            }
            catch
            {
                result = false;
            }

            return result;
        }

Answer 8

User-1171043462 posted

@Omar,

I would recommend write a SP that checks whether User Exists in your database and check whether User exists or not using RowsAffected returned by ExecuteNonQuery

Stored Proc

CREATE PROCEDURE InsertUser
	@userid VARCHAR(100),
	@name VARCHAR(100),
	@username VARCHAR(100),
	@password NVARCHAR(100),
	@role VARCHAR(100)
AS
BEGIN
    IF NOT EXISTS(SELECT UserId FROM tblUsers WHERE UserName = @username)
	BEGIN
		INSERT INTO tblusers VALUES (@userid,@name,@username,@password,@role)
	END
END

Code

using (MySqlCommand com = new MySqlCommand("InsertUser"))
{
        com.CommandType = CommandType.StoredProcedure.
        com.Parameters.AddWithValue("@userid",TextBox1.Text);
		com.Parameters.AddWithValue("@name", TextBox2.Text);
		com.Parameters.AddWithValue("@username", TextBox3.Text);
		com.Parameters.AddWithValue("@password", TextBox4.Text);
		com.Parameters.AddWithValue("@role", TextBox5.Text);
        com.Connection = con;
        con.Open();
        int rowsAffected = com.ExecuteNonQuery();
        con.Close();
		if(rowsAffected > 0)
		{
			//User does not Exists
		}
		else
		{
		    //User Exists
		}
}