Question

Here is a sample of the class I currently use for database interaction:

using System;
using System.Data;
using System.Collections.Generic;

// Libraries
using log4net;
using log4net.Config;
using MySql.Data.MySqlClient;

namespace AIC
{
    class DB
    {
        private static readonly ILog _logger = LogManager.GetLogger(typeof(DB));
        private MySqlConnection _connection;
        private MySqlCommand _cmd;
        private string _server;
        private string _database;
        private string _username;
        private string _password;

        //Constructor
        public DB(string server, string database, string username, string password)
        {
            log4net.Config.XmlConfigurator.Configure();

            _server = server;
            _database = database;
            _username = username;
            _password = password;

            _connection = new MySqlConnection(string.Format("SERVER={0};DATABASE={1};UID={2};PASSWORD={3};charset=utf8;", _server, _database, _username, _password));
        }

        public bool TestConnection()
        {
            try
            {
                _connection.Open();
                _connection.Close();
                _logger.Info("Connection test, passed...");
                return true;
            }
            catch (MySqlException ex)
            {
                _logger.Error(ex.ToString());
                return false;
            }
        }

        //open connection to database
        private bool Open()
        {
            try
            {
                if (_connection.State != ConnectionState.Open)
                    _connection.Open();
                _logger.Info("Starting connection to database...");
                return true;
            }
            catch (MySqlException ex)
            {
                _logger.Error(ex.ToString());
                return false;
            }
        }

        //Close connection
        private bool Close()
        {
            try
            {
                if (_connection.State != ConnectionState.Closed)
                    _connection.Close();
                _logger.Info("Closing connection to database...");
                return true;
            }
            catch (MySqlException ex)
            {
                _logger.Error(ex.ToString());
                return false;
            }
        }

        // Some basic functions
        public bool UserExist(string user)
        {
            string query = "SELECT user_id FROM users WHERE username=@name LIMIT 1";
            if (this.Open())
            {
                try
                {
                    // Assign the connection
                    _cmd = new MySqlCommand(query, _connection);

                    // Prepare to receive params
                    _cmd.Prepare();

                    // Fill up the params
                    _cmd.Parameters.AddWithValue("@name", user);

                    // returned count bool
                    bool result = Convert.ToInt32(_cmd.ExecuteScalar()) > 0;

                    // Close connection
                    this.Close();
                    return result;
                }
                catch (MySqlException ex)
                {
                    _logger.Error(ex.ToString());
                    this.Close();
                    return false;
                }
            }
            else
            {
                _logger.Error("You must be connected to the database before performing this action");
                return false;
            }
        }

        public bool AddUser(string user)
        {
            // .... add user to database
        }

        public bool DelUser(string user)
        {
            // .... del user from database
        }

        public int CountUsers()
        {
            // .... count total users from database
        }
    }
}

Currently, I don’t have any management for opening and closing the connections so it will always check wether the database is connected or not, perform the action and close it as shown in the UserExist function.

Considering this, it came to my attention that I might be closing my own connections in the middle or their transactions since I am using this in 2 different threads.

My doubt here is wether this simple class could lock my application for any reason making it unresponsive or cause me any troubles in the long run?

What should I consider, improve, etc.?

Would appreciate code samples.

Answer 1

Each thread should have its own connection instance, in your case probably an instance of Db.

But the problem would be solved (a lot) better by not storing a connection in your Db objects at all. The best pattern is to only use connections as local variables in a using() {} statement.

Currently, your class should implement IDisposable (just for the case where your try/catch logic fails).