Using C language to realize MySQL true paging

@[TOC] use C# Language implementation MYSQL True Pagination （wcf frame ）
True paging and false paging
Fake paging
　　 Get all the data from the database , Then the page is displayed on the interface . Access the database once , However, due to the large amount of data selected , So it takes a long time for the first time , But then every page is displayed directly 、 fast , Avoid multiple accesses to the database .
　 True Pagination
　　 Determine the quantity and content to display , Then every time I go to the database to get this small amount of data , The advantage is that the amount of data is small , The disadvantage is frequent access to the database . True paging is often used in large websites , For example, Baidu's image acquisition .

To improve efficiency , We use true paging ,

SQL Helper classes

 public class MySQLHelper
    {
    
        //public MySqlConnection GetConn()
        //{
    
        // 
        // MySqlConnection connect = new MySqlConnection(constructorString);

        // return connect;
        //}

        private MySqlConnection conn = null;// Database connection 
        private MySqlCommand cmd = null;// Operate on the database , That is to say, add, delete, modify and search 
        private MySqlDataReader sdr = null;// Read only from the database 

        public MySQLHelper()
        {
    
            string connStr = "server=192.168.60.54;port=3306;User Id=sentry;password=sentry;Database=sentry_system_dev;SslMode=none;Charset=utf8;";
            conn = new MySqlConnection(connStr);// Open the connection to the database , The connection is not successful at this time 


        }

        /// <summary>
        ///  Judge the connection of the data source 
        /// </summary>
        /// <returns> Connect </returns>
        private MySqlConnection GetConn()
        {
    
            if (conn.State == ConnectionState.Closed) // enumeration ConnectionState, Used to describe the current connection status of the data source 
            {
    
                conn.Open();// Connect to database 
            }
            return conn;
        }

        /// <summary>
        ///  adopt ExecuteQuery() Method . Execute with parameters SQL Query statement or stored procedure 
        /// </summary>
        /// <param name="cmdText"> Query text </param>
        /// <param name="paras"> Parameters </param>
        /// <param name="ct"> Execution type </param>
        /// <returns> Affected lines </returns>
        public DataTable ExecuteQuery(string cmdText, MySqlParameter[] paras, CommandType ct)
        {
    
            DataTable dt = new DataTable();// Instantiate a table in the database memory 
            cmd = new MySqlCommand(cmdText, GetConn());  //cmdText： The text of the query ;getConn(): How to connect to the database 
            cmd.CommandType = ct;// Specify the execution form of the command object , The default is text
            cmd.Parameters.AddRange(paras);// Add parameters to the parameter set 
            using (sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection)) // When executing a command , Associate  Connection  Associate when object is closed  DataReader  Object closed 
            {
    
                dt.Load(sdr);   // Fill the values in the provided data source into DataTable, If it already exists , Then merge 
            }
            return dt;  // Return table to DAL layer 
        }


      


        /// <summary>
        ///  Execute without parameters SQL Query statements or stored procedures 
        /// </summary>
        /// <param name="cmdText"> Inquire about SQL Statement or stored procedure </param>
        /// <param name="ct"> Command type </param>
        /// <returns> Returns the number of affected rows </returns>
        public DataTable ExecuteQuery(string cmdText, CommandType ct)
        {
    
            DataTable dt = new DataTable();
            cmd = new MySqlCommand(cmdText, GetConn());
            cmd.CommandType = ct;
            using (sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
            {
    
                dt.Load(sdr);
            }
            return dt;
        }


        /// <summary>
        ///  Execute database operations or stored procedures without parameters heihei
        /// </summary>
        /// <param name="cmdText"> Add, delete, change and check operation </param>
        /// <param name="ct"> Command type </param>
        /// <returns> Returns the number of affected rows </returns>
        public int ExecuteNonQuery(string cmdText, CommandType ct)
        {
    
            int res;
            cmd = new MySqlCommand(cmdText, GetConn());
            cmd.CommandType = ct;
            res = cmd.ExecuteNonQuery();
            if (conn.State == ConnectionState.Open)
            {
    
                conn.Close();
            }

            return res;
        }


        /// <summary>
        ///  Execute database operations or stored procedures with parameters 
        /// </summary>
        /// <param name="cmdText"> Add, delete, change and check operation </param>
        /// <param name="paras"> Parameters to query </param>
        /// <param name="ct"> Command type </param>
        /// <returns> Returns the number of affected rows </returns>
        public int ExecuteNonQuery(string cmdText, MySqlParameter[] paras, CommandType ct)
        {
    
            int res;
            using (cmd = new MySqlCommand(cmdText, GetConn()))
            {
    
                cmd.CommandType = ct;
                cmd.Parameters.AddRange(paras);
                res = cmd.ExecuteNonQuery();
            }
            return res;
        }

    }

Physical layer ：
public class FaceImageEntity
{
private string userID;// User name

    private string imageByte;// Picture bytecode 
    public byte[] ImageByte;

    private string faceToken;// Unique identification of the picture 

    public string UserID
    {
        get { return userID; }
        set { userID = value; }
    }

    public string  Sex { get; set; }
    public string  UserName { get; set; }
    public string FaceToken
    {
        get { return faceToken; }
        set { faceToken = value; }
    }

    public DateTime CreatTime { get; set; }
    public DateTime UpadateTime { get; set; }
    public int ISDelet { get; set; }
}

D layer ：

  /// <summary>
      ///  Get the data by entering the page size and page number 
      /// </summary>
      /// <param name="inputPageSidze"> Enter the size of each page </param>
      /// <param name="inputpageCode"> The number of pages to query </param>
      /// <returns></returns>
        public List<FaceImageEntity> PagingSelectAllImage(int inputPageSize, int inputpageCode)
        {
    

            List<FaceImageEntity> faceToken =new List<FaceImageEntity>();
            MySqlParameter[] sqlparams = new MySqlParameter[]
           {
    

                 new MySqlParameter("@is_Delet",0),
                
           };



           string sql= "SELECT * FROM t_faceimage_info where [email protected]_Delet order by create_Time desc limit " + (inputpageCode - 1) * inputPageSize + "," + inputPageSize;
         

            DataTable dataTable = sqlHelper.ExecuteQuery(sql, sqlparams, CommandType.Text);
            
                foreach (DataRow dataRow in dataTable.Rows)
                {
    

                    faceToken.Add(new FaceImageEntity
                    {
    
                        FaceToken = Convert.ToString(dataRow["face_Token"]),
                        ImageByte = (byte[])dataRow["image_Byte"],
                        UserID = Convert.ToString(dataRow["user_ID"]),
                        ISDelet = Convert.ToInt32(dataRow["is_Delet"]),
                        Sex = Convert.ToString(dataRow["sex"]),
                        UserName = Convert.ToString(dataRow["user_Name"]),
                        CreatTime = Convert.ToDateTime(dataRow["create_Time"]),
                        UpadateTime = Convert.ToDateTime(dataRow["update_Time"])


                    }); ;

                }

            return faceToken;


        }

B layer ：

/// <summary>
        ///  By entering the size of each page and getting the page number ,
        /// </summary>
        /// <param name="inputPageSidze"> The size of each page </param>
        /// <param name="inputpageCode"> Look up the page </param>
        /// <returns> Return the data </returns>
        public List<FaceImageEntity> PagingSelectAllImage(int inputPageSidze, int inputpageCode)
        {
    
            return FaceImageDAL.PagingSelectAllImage(inputPageSidze,inputpageCode);
        }