Develop Reference

How to check if user in mysql database exists (in c#)

So I know this is a often asked question but I want to check if the username is already taken in the database using c#. I tried this:
MySqlCommand cmd2 = new MySqlCommand("SELECT * FROM tablename WHERE(name = '" + tb1.Text + "');");
cmd2.Connection = connect;
connect.Open();
string unt = "";
try
{
MySqlDataReader dr;
dr = cmd.ExecuteReader();
while (dr.Read())
{
unt= dr.GetString("name");
}
dr.Close();
}
catch (Exception ex)
{
errorbox.Content = ex.Message;
}
finally
{
connect.Close();
}
if(unt == "" || unt == "0") {
continuel = false;
tb2.Text = "User " +tb1.Text+ " doesn't exist!";
Popup1.IsOpen = true;
}
Its a WPF project and the variable 'continuel' is set to true by default. The code doesn't recognize if a user doesn't exist.

First off your code is vulnerable to sql inject, you should never concatenate values into a query. secondly you can do a count and execute a scalar. Not I stripped down your code a little you'll have to add error handling back.
bool userExists = false;
private String sql = "SELECT COUNT(*) FROM tableName WHERE name = #usernameparam;";
MySqlCommand m = new MySqlCommand(sql);
m.Parameters.AddWithValue("#usernameparam", tb1.Text.Trim());
int userCount = Convert.ToInt32(m.ExecuteScalar());
if(userCount>0)
{
userExists = true;
}
//use userExists variable to evaluate if user exists

c# Using Two MysqlReaders

I want to retrive data from two differentables in my mysql data base so i created one connection and two readers, The second reader is not returning any results but the first reader is.
public List<BlogContentItemClass> BCITLIST = new List<BlogContentItemClass>();
// GET: api/BlogContents
[HttpGet]
public List<BlogContentItemClass> Get(string id)
{
string sqlstring = "server=; port= ; user id =;Password=;Database=;";
MySqlConnection conn = new MySqlConnection(sqlstring);
try
{
conn.Open();
}
catch (MySqlException ex)
{
throw ex;
}
string Query = "SELECT * FROM test.blogtable where `id` = '" + id + "' ";
MySqlCommand cmd = new MySqlCommand(Query, conn);
MySqlDataReader MSQLRD = cmd.ExecuteReader();
BlogContentItemClass BCIT = new BlogContentItemClass();
Label BLOGID = new Label();
if (MSQLRD.HasRows)
{
while (MSQLRD.Read())
{
string TC = (MSQLRD["Topic"].ToString());
string CT = (MSQLRD["Category"].ToString());
string SM = (MSQLRD["Summary"].ToString());
string BID = (MSQLRD["id"].ToString());
BCIT.TopicSaved1 = TC;
BCIT.CategoriesSaved1 = CT;
BCIT.SummarySaved1 = SM;
BLOGID.Text = BID;
BCIT.TotalBodyStackLayout1.Add("Hello");
}
}
BCITLIST.Add(BCIT);
MSQLRD.Close();
string Query1 = "SELECT * FROM test.blogbodytable where `BlogID` = '" + BLOGID.Text + "' ";
MySqlCommand cmd1 = new MySqlCommand(Query1, conn);
MySqlDataReader MSQLRD1 = cmd1.ExecuteReader();
if (MSQLRD1.HasRows)
{
while (MSQLRD1.Read())
{
string BLOGBODY ;
BLOGBODY = (MSQLRD1["BlogBody"].ToString());
BCIT.TotalBodyStackLayout1.Add(BLOGBODY);
}
}
BCITLIST.Add(BCIT);
conn.Close();
return BCITLIST;
}
from my code the line BCIT.TotalBodyStackLayout1.Add("Hello"); in the first reader does add "hello" to the BCIT.TotalBodyStacklayout1, but the line BCIT.TotalBodyStackLayout1.Add( BLOGBODY); does not work, what am i doing wrong?

Can you be more specific what you mean by 'BCIT.TotalBodyStackLayout1.Add(BLOGBODY);' does not work. Are you getting any exception? or if BLOGBODY coming empty? There are few primitive troubleshooting steps you can perform to nail-down the issue
confirm what BLOGID.Text you are getting from your previous query and corresponding data is available in test.blogbodytable for that id.
if (MSQLRD1.HasRows) is resolving to true
Were you able to get inside while (MSQLRD1.Read())

MySqlCommand: no rows returned

I have a database created in a server and I added a row by MySql query browser for testing. This row is visible either with PhpMyAdmin or MySql query browser.
But when I want to reach this table within my program it says me there is no rows (reader.HasRows = false)
cs is the connection string in PublicVariables class
Here is the code
public static int checkuser(string myuser, string mypass)
{
try
{
using (MySqlConnection conn = new MySqlConnection(PublicVariables.cs))
{
string MypassMd5 = MakeMD5(mypass);
conn.Open();
if (conn == null)
Environment.Exit(0);
using (MySqlCommand cmd =
new MySqlCommand("SELECT username, password " + "FROM Users WHERE username = 'myuser'" ,conn))
{
using (MySqlDataReader reader = cmd.ExecuteReader())
{
//DateTime mytime = DateTime.Now ;
if (reader.HasRows)
{
if (Convert.ToString(reader["password"]) != MypassMd5)
{
reader.Close();
conn.Close();
return -1;
}
else
{
PublicVariables.UserId = Convert.ToString(reader["username"]);
PublicVariables.UserDegre = Convert.ToInt16(reader["userdegre"]);
conn.Close();
reader.Close();
return 1;
}
}
else
{
reader.Close();
conn.Close();
return 2;
}
}
}
}
}
catch (MySqlException ex)
{
MessageBox.Show(ex.ToString());
}
return 0;
}
What's wrong in my code?

Well the primary error is in your command string , myuser is a variable and you cannot pass its value putting the variable name inside quotes.
new MySqlCommand("SELECT username, password FROM Users WHERE username = 'myuser'" ,conn)
instead this line should be converted to use a parameterized query
string commandText = "SELECT username, password, userdegre FROM Users WHERE username = #uname";
using (MySqlCommand cmd = new MySqlCommand(commandText ,conn)
{
cmd.Parameters.AddWithValue("#uname", myuser);
....
Looking at your code you have another error after this. You try to read the field userdegre, but this field is not retrieved by your query, so you need to add it to the list of retrieved fields.
But the only field you really need to know is userdegre because you already know the username and the password, so you could remove the datareader and use ExecuteScalar and pass the username and the password as parameters for the WHERE clause. If you get anything in return then you are sure that your user is authenticated by the database.
string commandText = "SELECT userdegre FROM Users WHERE username = #uname AND Password =#pwd";
using(MySqlCommand cmd = new MySqlCommand( commandText ,conn))
{
cmd.Parameters.AddWithValue("#uname", myuser);
cmd.Parameters.AddWithValue("#pwd", MypassMd5);
var result = cmd.ExecuteScalar();
if(result != null)
{
PublicVariables.UserId = myuser;
PublicVariables.UserDegre = result.ToString();
}
}

Don't check reader.HasRows. You need to call reader.Read(), and check the result of that.
Also, some side issues:
MD5 is incredibly weak for a password hash. Really. Just don't use it for that. Look into bcrypt as a much better alternative. Better still if you're not writing authentication code yourself at all. Look for a library for help to get this stuff right... it's just so easy to write authentication code that seems to work, passes all your tests, but has a subtle flaw that gets you hacked a few months down the road.
No need to call conn.Close(). That's what your using blocks are for. They will handle this for you.
I'd remove the try/catch as well. Since you're already returning error conditions to the calling code, I'd leave that as the place where errors are processed, such that your try/catch should go at that level.
You're looking for userdegre in the results that was not in the select list.
Parameterized queries are your friend.
Put it all together you and you end up with this:
public static int checkuser(string myuser, string mypass)
{
string passHash = BCrypt(mypass); //Need to get bcyrpt library and make the function
using (MySqlConnection conn = new MySqlConnection(PublicVariables.cs))
using (MySqlCommand cmd =
new MySqlCommand("SELECT username, password, userdegre FROM Users WHERE username = #user" ,conn))
{
cmd.Parameters.Add("#user", SqlDbType.NVarChar, 20).Value = myuser;
conn.Open();
using (MySqlDataReader reader = cmd.ExecuteReader())
{
if (!reader.Read()) return 2;
if (Convert.ToString(reader["password"]) != MypassMd5) return -1;
PublicVariables.UserId = Convert.ToString(reader["username"]);
PublicVariables.UserDegre = Convert.ToInt16(reader["userdegre"]);
return 1;
}
}
}

I would try something like this new MySqlCommand("SELECT username, password, userdegre " + "FROM Users WHERE username = 'myuser'" ,conn))
adding userdegre the column name in your select statement.

Finally for c# 2008 net 3.5 WORKING COPY of this after the help of #Joel and # Steve is as this:
public static int usertrue(string myuser, string mypass)
{
try
{
using (MySqlConnection conn = new MySqlConnection(PublicVariables.cs))
{
string MypassMd5 = MakeMD5(mypass);
using (MySqlCommand cmd =
new MySqlCommand("SELECT username, password ,userdegre FROM Users WHERE username = #user",conn))
{
cmd.Parameters.Add("#user", MySqlDbType.VarChar, 15).Value = myuser;
conn.Open();
using (MySqlDataReader reader = cmd.ExecuteReader())
{
if (!reader.Read()) return 2;
if (Convert.ToString(reader["password"]) != MypassMd5) return -1; {
PublicVariables.UserId = Convert.ToString(reader["username"]);
PublicVariables.UserDegre = Convert.ToInt16(reader["userdegre"]);
return 1;
}
}
}
}
}

How to select a value with results from another column

i am using C# and i need to develop a check system for a mysql user and password.
So far what ive come up with is this and the error i get is that it is the wrong syntax...
public bool VerifyUser(string username, string password)
{
string returnValue = "";
string Query = "SELECT Pass FROM Base_Character WHERE User='" + username + "'";
MySqlCommand verifyUser = new MySqlCommand(Query, this.sqlConn);
try
{
verifyUser.ExecuteNonQuery();
MySqlDataReader myReader = verifyUser.ExecuteReader();
while (myReader.Read() != false)
{
returnValue = myReader.GetString(0);
}
myReader.Close();
}
catch (Exception excp)
{
Exception myExcp = new Exception("Could not verify user. Error: " +
excp.Message, excp);
throw (myExcp);
}
if (returnValue == password)
{
return false;
}
else
{
return true;
}
}

ExecuteNonQuery is for DELETE, INSERT and UPDATE. Whenever you want data returned as rows from database, use ExecuteReader
Your query should check the username and password together, if they exist in one record then the row is returned else nothing is returned.
You still need more to learn about coding/database programming using .Net
public bool VerifyUser(string username, string password)
{
bool returnValue = false;
string Query = "SELECT 1 FROM Base_Character WHERE User='" + username + "' AND pass='"+password+"'";
try
{
MySqlCommand command = new MySqlCommand(Query, this.sqlConn);
MySqlDataReader myReader = command.ExecuteReader();
if(myReader.Read())
{
returnValue = true;
}
myReader.Close();
}
catch (Exception excp)
{
throw;
}
return returnValue;
}
You should probably not throw a custom exception since you are using boolean
if(VerifyUser("user123", "******"))
{
//Congratulations
}
else
{
//Unable to log you in
}

Thanks guys, but this calls for a custom encryption that mysql cant hold or process, my main error was ovrlooking the executenonquery(), so i had to make the code like this:
if (AuthorizeTools.Encrypt.Password(Database.getPassword) != Password) //Password is already encrypted
Then set the mysql function to:
public string getPassword(string username)
{
string returnValue = "";
string Query = "SELECT Pass FROM Base_Character where (User=" +
"'" + username + "') LIMIT 1";
MySqlCommand checkUser = new MySqlCommand(Query, this.sqlConn);
try
{
checkUser.ExecuteNonQuery();
MySqlDataReader myReader = checkUser.ExecuteReader();
while (myReader.Read() != false)
{
returnValue = myReader.GetString(0);
}
myReader.Close();
}
catch (Exception excp)
{
Exception myExcp = new Exception("Could not grab password: " +
excp.Message, excp);
throw (myExcp);
}
return (returnValue);
}

When ASP.NET username exists, change to username(x)

Using SQL Membership Provider for ASP.NET membership. I'm using first.last as the username, which is created programmatically from the user details filled in on a form.
When user submits the form, I want to be able to check if the username exists, and change it to username1 if it does, check username1 exists, and make it username2 if it exists, etc. until it is a unique username.
I don't know how to do stored procedures, so I'm trying to use a SQLDataReader to check if username exists.
The problem is my loop. The logic is basically to set a boolean and keep looping and adding 1 to the counter, until it doesn't find a duplicate. I have stepped through this many times, and even when it sets the boolean to false, it keeps looping.
Ideas please?
Code behind:
protected void Membership_add()
{
SqlConnection con = new SqlConnection(connectionString);
string NewUserNameString = FirstName.Text + "." + LastName.Text;
//Check for duplicate aspnet membership name and add a counter to it if exists
// Check for valid open database connection before query database
bool match = true;
SqlDataReader _SqlDataReader = null;
string TestNameString = NewUserNameString;
string selectDupeString = "SELECT UserId FROM aspnet_Users WHERE UserName = '" + TestNameString + "'";
SqlCommand SQLdatareaderCmd = new SqlCommand(selectDupeString, con);
int UserNameCounter = 0;
con.Open();
while (match = true)
{
//Open the connection
try
{
//Read the table
_SqlDataReader = SQLdatareaderCmd.ExecuteReader();
}
catch (Exception ex)
{
lblDatareaderEx.Text = "An Exception occurred. " + ex.Message + " " + ex.GetType().ToString();
}
if (_SqlDataReader.HasRows)
{
//match = true;
//increase counter by 1 for each record found and change First.Name to First.Namex
TestNameString = NewUserNameString;
UserNameCounter = UserNameCounter + 1;
TestNameString = TestNameString + UserNameCounter.ToString();
_SqlDataReader.Close();
_SqlDataReader.Dispose();
selectDupeString = "SELECT UserId FROM aspnet_Users WHERE UserName = '" + TestNameString + "'";
SQLdatareaderCmd = new SqlCommand(selectDupeString, con);
}
else
{
// close sql reader
_SqlDataReader.Close();
_SqlDataReader.Dispose();
//get out of loop
match = false;
}
}
con.Close();
con.Dispose();
}

This line:
while (match = true)
does an assignment.
If you want your code to work you have to do a comparison:
while (match == true)
Or, since your variable is already a bool, you can just use the variable directly:
while(match)

At the moment you're setting match rather than comparing it's value.
Try setting while (match = true) to while (match == true)

If you break your code out into smaller blocks, the code becomes simpler and easer to read.
private string MembershipAddUser(string firstName, string lastName)
{
string username = firstName + "." + lastName;
int i = 0;
while (UserExists(username))
{
i++;
username = firstName + "." + lastName + i.ToString();
}
return username;
}
private bool UserExists(string username)
{
string sql = "SELECT COUNT(*) FROM dbo.aspnet_Users WHERE UserName = #UserName";
SqlConnection connection = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand(sql, connection);
command.Parameters.AddWithValue("#UserName", username);
using (connection)
{
connection.Open();
int count = (int) command.ExecuteScalar();
return (count != 0);
}
}