WPF_Practice/PacticeSolution/MSSQL_MVVM_Sample/Database/SqlManager.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MSSQL_MVVM_Sample.Structure;

namespace MSSQL_MVVM_Sample.Database
{
    public sealed class SqlManager : Singleton<SqlManager>
    {
        public event ExceptionEventHandler ExceptionEvent;

        public SqlConnection Connection { get; set; }
        public string ConnectionString { get; set; }

        private SqlCommand _lastExecutedCommand;
        private int _retryCount;

        public bool IsRunning { get { return CheckDBConnected(); } }

        public static SqlManager GetNewInstanceConnection()
        {
            if (Instance == null)
                return null;

            SqlManager sqlManager = new SqlManager()
            {
                ConnectionString = Instance.ConnectionString
            };
            sqlManager.GetConnection();
            sqlManager.ExceptionEvent = Instance.ExceptionEvent;

            return sqlManager;
        }

        public void SetConnectionString(string connectionString)
        {
            ConnectionString = connectionString;
        }

        public bool GetConnection()
        {
            try
            {
                if (Connection != null)
                {
                    Connection.Close();
                    Connection.Dispose();
                    Connection = null;
                }

                Connection = new SqlConnection(ConnectionString);
                Connection.Open();

                if (Connection.State != ConnectionState.Open)
                    return false;

                return true;
            }
            catch (Exception ex)
            {
                HandleExceptionEvent("GetConnection", ex);
                return false;
            }
        }

        private bool CheckDBConnected()
        {
            try
            {
                string query = "SELECT GETDATE() Date";
                SqlCommand cmd = new SqlCommand()
                {
                    Connection = Connection,
                    CommandText = query,
                };

                SqlDataReader result = cmd.ExecuteReader();
                if (result == null || !result.HasRows)
                    return false;

                return true;
            }
            catch (Exception ex)
            {
                HandleExceptionEvent("CheckDBConnected", ex);
                return false;
            }
        }

        public int ExecuteNonQuery(string query)
        {
            try
            {
                lock (this)
                {
                    SqlCommand cmd = new SqlCommand()
                    {
                        Connection = Connection,
                        CommandText = query,
                    };

                    return cmd.ExecuteNonQuery();
                }
            }
            catch (Exception ex)
            {
                HandleExceptionEvent("ExecuteNonQuery", ex);
                return -1;
            }
        }

        public int ExecuteNonQuery(string query, SqlParameter[] sqlParams)
        {
            try
            {
                lock (this)
                {
                    SqlCommand cmd = new SqlCommand()
                    {
                        Connection = Connection,
                        CommandText = query,
                    };

                    for (int i = 0; i < sqlParams.Length; i++)
                    {
                        cmd.Parameters.Add(sqlParams);
                    }

                    return cmd.ExecuteNonQuery();
                }
            }
            catch (Exception ex)
            {
                HandleExceptionEvent("ExecuteNonQuery with sqlParams", ex);
                return -1;
            }
        }

        public DataSet ExecuteSelectQuery(string query)
        {
            try
            {
                lock (this)
                {
                    SqlCommand cmd = new SqlCommand()
                    {
                        Connection = Connection,
                        CommandText = query,
                    };
                    SqlDataAdapter adt = new SqlDataAdapter()
                    {
                        SelectCommand = cmd,
                    };

                    DataSet ds = new DataSet();
                    adt.Fill(ds);
                    return ds;
                }
            }
            catch (Exception ex)
            {
                HandleExceptionEvent("ExecuteNonQuery with sqlParams", ex);
                return null;
            }
        }

        private void HandleExceptionEvent(string id, Exception ex)
        {
            if (ExceptionEvent != null)
                ExceptionEvent(id, ex);
        }
    }
}