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  • 1 Post By nvoigt

OleDB connection

This is a discussion on OleDB connection within the C# Programming forums, part of the General Programming Boards category; i originally wrote this code in visual basic and it worked fine but when i tried rewriting it in c# ...

  1. #1
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    OleDB connection

    i originally wrote this code in visual basic and it worked fine but when i tried rewriting it in c# it raised an error saying 'dr is a variable but is being used like a method' , please how do i fix this?

    Code:
    public bool validateuser(string password, string username)
    {
        OleDbCommand cmd = new OleDbCommand();
        dbconnection db = new dbconnection();
        cmd.Connection = db.connection;
        cmd.CommandText = "select * from userlogin where password = ? and username = ?";
        cmd.CommandType = CommandType.Text;
        cmd.Parameters.AddWithValue("", password);
        cmd.Parameters.AddWithValue("", username);
    
        bool found = false;
        OleDbDataReader dr = default(OleDbDataReader);
        dr = cmd.ExecuteReader;
        if (dr.Read) {
            found = true;
        }
    
        return found;
    }

  2. #2
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    Code:
    OleDbDataReader dr = cmd.ExecuteReader();
    And

    Code:
    if (dr.Read())
    The clue was in the exception.

    Also don't forget to Dispose cmd, db and dr, or better yet, use 'using' statements.
    Last edited by theoobe; 11-29-2012 at 05:36 PM.

  3. #3
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    This is the full code it now gives me the same error when i try using dr("username").(dr is a variable but is being used like a method)
    i am now learning c# and am trying to search and retreive from a database.

    Code:
    public bool validateuser(string password, string username)
    {
        namespace ConsoleApplication1
    {
        class @dbconnection
        {
            private static OleDbConnection conn = new OleDbConnection();
    
            static void con()
            {
                conn.ConnectionString = "Provider=MSDAORA;Data Source=xe;Persist Security Info=True;User ID=GOL;Password=kaRkaRr0t";
                conn.Open();
            }
    
             public new OleDbConnection connection
             {
                get
                {
                     return conn;
                }              
             }      
        }
    
        class @test
        {
            private static string user;
            public static string username
            {
                get
                {
                    return user;
                }
                set
                {
                    user = value;
                }
            }
    
            public static void getname()
            {
                OleDbCommand cmd = new OleDbCommand();
                dbconnection db = new dbconnection();
                cmd.Connection = db.connection;
                cmd.CommandText = "select * from userlogin where password = 'user'";
                cmd.CommandType = CommandType.Text;
                
                OleDbDataReader dr =  default(OleDbDataReader);
                dr = cmd.ExecuteReader();
                if(dr.Read())
                {
                    username = dr("username") ;
                }
           
            }
        }
    }

  4. #4
    the hat of redundancy hat nvoigt's Avatar
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    That's a lot of overhead to get confused. Try to keep your programs simpler while learning new things.

    Code:
    using System;
    using System.Data.OleDb;
    
    namespace ConsoleApplication1
    {
      internal class Program
      {
        public static bool ValidateUser(string password, string username)
        {
          const string connectionString = "Provider=MSDAORA;Data Source=xe;Persist Security Info=True;User ID=GOL;Password=kaRkaRr0t";
          const string sql = "SELECT COUNT(*) FROM USERLOGIN WHERE USERNAME = @name AND PASSWORD = @password";
    
          using (var connection = new OleDbConnection(connectionString))
          {
            using (var command = new OleDbCommand(sql, connection))
            {
              command.Parameters.AddWithValue("@name", username);
              command.Parameters.AddWithValue("@password", password);
    
              return Convert.ToInt32(command.ExecuteScalar()) > 0;
            }
          }
        }
    
        public static void Main(string[] args)
        {
          const string user = "test";
          const string password = "secret";
    
          bool isValid = ValidateUser(password, user);
    
          Console.WriteLine("{0}/{1} is {2}", user, password, isValid ? "valid" : "invalid");
        }
      }
    }
    I couldn't test it here, but it should demostrate what steps you have to take to authenticate somebody.
    Last edited by nvoigt; 12-01-2012 at 10:46 AM. Reason: replaced ExecuteReader with ExecuteScalar
    theoobe likes this.
    hth
    -nv

    She was so Blonde, she spent 20 minutes looking at the orange juice can because it said "Concentrate."

    When in doubt, read the FAQ.
    Then ask a smart question.

  5. #5
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    I'm not really looking for how to authenticate i'm just looking for how to retrieve a value from a database.

  6. #6
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    Use square brackets...

    Code:
    dr["username"]
    Returning to my earlier point about disposing your database objects, it is bad practice to leave database connections lingering, which is what you are doing by failing to dispose these objects.

  7. #7
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    Okay i'll dispose the database objects but with your answer to my question(using square brackets) i tried it and got this error :

    "Only assignment, call, increment, decrement, and new object expressions can be used as a statement"

  8. #8
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    Probably needs casting...

    Code:
    if(dr.Read())
        username = (String)dr["username"];

  9. #9
    Gawking at stupidity
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    Quote Originally Posted by nvoigt
    return Convert.ToInt32(command.ExecuteReader()) > 0;
    I think you meant command.ExecuteScalar(). Or can you convert a DataReader to Int32 and I just never knew it?
    If you understand what you're doing, you're not learning anything.

  10. #10
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    this is the same way i did it in vb and i understood it but now i'm haiving trouble implementing it in c#, i've tried "username = (string)dr["username"]" and i still get the same error so i don't think that is the problem. The main issue is i want to retrieve the username from the database into a variable using oledb, so if anyone has another way of doing it could you please show me.

  11. #11
    the hat of redundancy hat nvoigt's Avatar
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    Quote Originally Posted by itsme86 View Post
    I think you meant command.ExecuteScalar(). Or can you convert a DataReader to Int32 and I just never knew it?
    Oops, absolutely! I'll change it in the above code.
    hth
    -nv

    She was so Blonde, she spent 20 minutes looking at the orange juice can because it said "Concentrate."

    When in doubt, read the FAQ.
    Then ask a smart question.

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