策略模式实现支持多种类数据库的DBHelp（推荐--arvin）

来自：http://www.cnblogs.com/springyangwc/archive/2013/03/17/2964428.html#2636446

概述

需求

有时我们的系统需要支持多种数据库，如即要支持MSSQL server又要同时支持Oracle database.而如果我们为些实现两套数据库操作的方式，就会不能很好的达到软件设计的目标：高内聚，低偶合。

设计

采取策略模式（Strategy），它定义了一系列的算法，并将每一个算法封装起来，而且使它们还可以相互替换。策略模式让算法的变化不会影响到使用算法的客户。

优点：

1、 简化了单元测试，因为每个算法都有自己的类，可以通过自己的接口单独测试。  
2、 避免程序中使用多重条件转移语句，使系统更灵活，并易于扩展。   
3、 遵守大部分GRASP原则和常用设计原则，高内聚、低偶合。

缺点：  
1、 因为每个具体策略类都会产生一个新类，所以会增加系统需要维护的类的数量。   
2、 在基本的策略模式中，选择所用具体实现的职责由客户端对象承担，并转给策略模式的Context对象。（这本身没有解除客户端需要选择判断的压力，而策略模式与简单工厂模式结合后，选择具体实现的职责也可以由Context来承担，这就最大化的减轻了客户端的压力。）

DBHelp设计目标，同时支持Sqlite、Oracle 、MySql 、MsSql,类UML图设计如下：

有了上面的设计图如后，我们先创建Enums：

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/********************************************************************************

** Class Name:   Enums

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     Enums  class

*********************************************************************************/

namespace BlogDBHelp

{

    using System;

    [Serializable]

    public enum SqlSourceType

    {

        Oracle,

        MSSql,

        MySql,

        SQLite

    }

}

再创建IDBHelp接口：

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/********************************************************************************

** Class Name:   IDBHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     IDBHelp interface

*********************************************************************************/

namespace BlogDBHelp

{

    using System.Collections.Generic;

    using System.Data;

    using System.Data.Common;

    public interface IDBHelp

    {

        /// <summary>

        /// Gets the connection string

        /// </summary>

        string ConnectionString { get; set; }

        /// <summary>

        /// Gets or sets the max connection count

        /// </summary>

        int MaxConnectionCount { get; set; }

        /// <summary>

        /// Gets or sets the sql source type

        /// </summary>

        SqlSourceType DataSqlSourceType { get; }

        /// <summary>

        /// Execute query by stored procedure

        /// </summary>

        /// <paramname="cmdText">stored procedure</param>

        /// <returns>DataSet</returns>

        DataSet ExecuteQuery(string cmdText);

        /// <summary>

        /// Execute non query by stored procedure and parameter list

        /// </summary>

        /// <paramname="cmdText">stored procedure</param>

        /// <returns>execute count</returns>

        int ExecuteNonQuery(string cmdText);

        /// <summary>

        /// Execute scalar by store procedure

        /// </summary>

        /// <paramname="cmdText">store procedure</param>

        /// <returns>return value</returns>

        object ExecuteScalar(string cmdText);

        /// <summary>

        /// Get data base parameter by parameter name and parameter value

        /// </summary>

        /// <paramname="key">parameter name</param>

        /// <paramname="value">parameter value</param>

        /// <returns>sql parameter</returns>

        DbParameter GetDbParameter(string key, object value);

        /// <summary>

        /// Get data base parameter by parameter name and parameter value

        /// and parameter direction

        /// </summary>

        /// <paramname="key">parameter name</param>

        /// <paramname="value">parameter value</param>

        /// <paramname="direction">parameter direction </param>

        /// <returns>data base parameter</returns>

        DbParameter GetDbParameter(string key, object value, ParameterDirection direction);

        /// <summary>

        /// Read entity list by  store procedure

        /// </summary>

        /// <typeparamname="T">entity</typeparam>

        /// <paramname="cmdText">store procedure</param>

        /// <returns>entity list</returns>

        List<T> ReadEntityList<T>(string cmdText) where T : new();

        /// <summary>

        /// Get dictionary result by store procedure and parameters and string list

        /// </summary>

        /// <paramname="cmdText">store procedure</param>

        /// <paramname="stringlist">string list</param>

        /// <returns>result list</returns>

        List<Dictionary<string, object>> GetDictionaryList(string cmdText,

                                                          List<string> stringlist);

        /// <summary>

        /// Batch execute ExecuteNonQuery by cmdText list

        /// </summary>

        /// <paramname="cmdList">cmd text list</param>

        /// <returns>execute true or not</returns>

        bool BatchExecuteNonQuery(List<string> cmdList);

    }

}

再创建AbstractDBHelp 抽象类：

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/********************************************************************************

** Class Name:   AbstractDBHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     AbstractDBHelp interface

*********************************************************************************/

namespace BlogDBHelp

{

    using System;

    using System.Collections.Generic;

    using System.Configuration;

    using System.Data;

    using System.Data.Common;

    using System.Reflection;

    using System.Threading;

    public abstract class AbstractDBHelp : IDBHelp

    {

        #region Private Property

        private static int _currentCount;

        private int _maxConnectionCount;

        private string _connectionString;

        #endregion

        #region Private Methods

        private void AddConnection()

        {

           if (_currentCount <MaxConnectionCount)

               _currentCount++;

           else

           {

               while (true)

               {

                   Thread.Sleep(5);

                   if (_currentCount < MaxConnectionCount)

                   {

                       _currentCount++;

                       break;

                   }

               }

           }

        }

        private void RemoveConnection()

        {

           _currentCount--;

        }

        /// <summary>

        /// Execute query by stored procedure and parameter list

        /// </summary>

        /// <paramname="cmdText">stored procedure and parameter list</param>

        /// <paramname="parameters">parameter list</param>

        /// <returns>DataSet</returns>

        private DataSet ExecuteQuery(string cmdText, List<DbParameter> parameters)

        {

           using (var conn = GetConnection(ConnectionString))

           {

               conn.Open();

               using (var command = conn.CreateCommand())

               {

                   var ds = new DataSet();

                   PrepareCommand(command, conn, cmdText, parameters);

                   var da = GetDataAdapter(command);

                   da.Fill(ds);

                   return ds;

               }

           }

        }

        /// <summary>

        /// Execute non query by stored procedure and parameter list

        /// </summary>

        /// <paramname="cmdText">stored procedure</param>

        /// <paramname="parameters">parameter list</param>

        /// <returns>execute count</returns>

        private int ExecuteNonQuery(string cmdText, List<DbParameter> parameters)

        {

           using (var conn = GetConnection(ConnectionString))

           {

               conn.Open();

               using (var command = conn.CreateCommand())

               {

                   PrepareCommand(command, conn, cmdText, parameters);

                   return command.ExecuteNonQuery();

               }

           }

        }

        public bool BatchExecuteNonQuery(List<string> cmdList)

       {

           using (var conn = GetConnection(ConnectionString))

           {

               conn.Open();

               using (var transaction = conn.BeginTransaction())

               {

                   foreach (var cmdText in cmdList)

                   {

                       if (string.IsNullOrEmpty(cmdText)) continue;

                       using (var command = conn.CreateCommand())

                       {

                           try

                           {

                               command.CommandText = cmdText;

                               command.Transaction = transaction;

                               command.ExecuteNonQuery();

                           }

                           finally

                           {

                               command.CommandText = null;

                               command.Dispose();

                           }

                       }

                   }

                   try

                   {

                       transaction.Commit();

                       return true;

                   }

                   catch

                   {

                       transaction.Rollback();

                       return false;

                   }

                   finally

                   {

                       transaction.Dispose();

                       conn.Dispose();

                       conn.Close();

                       cmdList.Clear();

                   }

               }

           }

       }

       /// <summary>

       /// Execute reader by store procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">store procedure</param>

       /// <paramname="parameters">parameter list</param>

       /// <paramname="conn">database connection </param>

       /// <returns>data reader</returns>

       public DbDataReader ExecuteReader(string cmdText, List<DbParameter> parameters, out DbConnection conn)

       {

           conn = GetConnection(ConnectionString);

           conn.Open();

           AddConnection();

           var command = conn.CreateCommand();

           PrepareCommand(command, conn, cmdText, parameters);

           var dataReader = command.ExecuteReader();

           RemoveConnection();

           return dataReader;

       }

       /// <summary>

       /// Execute reader by store procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">store procedure</param>

       /// <paramname="parameters">parameter list</param>

       /// <returns>data reader</returns>

       private List<T> ReadEntityList<T>(string cmdText, List<DbParameter> parameters) where T : new()

       {

           using (var conn = GetConnection(ConnectionString))

           {

               conn.Open();

               using (var command = conn.CreateCommand())

               {

                   PrepareCommand(command, conn, cmdText, parameters);

                   var dataReader = command.ExecuteReader();

                   return ReadEntityListByReader<T>(dataReader);

               }

           }

       }

       /// <summary>

       /// Read entity list by reader

       /// </summary>

       /// <typeparamname="T">entity</typeparam>

       /// <paramname="reader">data reader</param>

       /// <returns>entity</returns>

       private List<T> ReadEntityListByReader<T>(DbDataReader reader) where T : new()

       {

           var listT = new List<T>();

           using (reader)

           {

               while (reader.Read())

               {

                   var fileNames = new List<string>();

                   for (int i = 0; i <reader.VisibleFieldCount; i++)

                   {

                       fileNames.Add(reader.GetName(i));

                   }

                   varinst=newT();

                   foreach (var pi in typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public))

                   {

                       if (!fileNames.Exists(fileName => string.Compare(fileName, pi.Name, StringComparison.OrdinalIgnoreCase) == 0))

                           continue;

                       object obj;

                       try

                       {

                           obj = reader[pi.Name];

                       }

                       catch (Exception)

                       {

                           continue;

                       }

                       if (obj == DBNull.Value || obj == null)

                           continue;

                       var si = pi.GetSetMethod();

                       if (si == null)

                           continue;

                       if (pi.PropertyType == typeof(bool?))

                           pi.SetValue(inst, Convert.ToBoolean(obj), null);

                       else if (pi.PropertyType == typeof(string))

                           pi.SetValue(inst, obj.ToString(), null);

                       else if (pi.PropertyType == typeof(Int32))

                           pi.SetValue(inst, Convert.ToInt32(obj), null);

                       else if (pi.PropertyType == typeof(Int64))

                           pi.SetValue(inst, Convert.ToInt64(obj), null);

                       else if (pi.PropertyType == typeof(decimal))

                           pi.SetValue(inst, Convert.ToDecimal(obj), null);

                       else

                           pi.SetValue(inst, obj, null);

                   }

                   listT.Add(inst);

               }

           }

           return listT;

       }

       /// <summary>

       /// Get Dictionary list by string list

       /// </summary>

       /// <paramname="cmdText">Store procedure</param>

       /// <paramname="parameters">parameter list</param>

       /// <paramname="stringlist">string list</param>

       /// <returns>result list</returns>

       private List<Dictionary<string, object>> GetDictionaryList(string cmdText, List<DbParameter> parameters, List<string> stringlist)

       {

           using (var conn = GetConnection(ConnectionString))

           {

               AddConnection();

               using (var command = conn.CreateCommand())

               {

                   PrepareCommand(command, conn, cmdText, parameters);

                   var dataReader = command.ExecuteReader();

                   RemoveConnection();

                   return ReadStringListByReader(dataReader, stringlist);

               }

           }

       }

       /// <summary>

       /// Read dictionary list by reader and string list

       /// </summary>

       /// <paramname="reader">Db data reader</param>

       /// <paramname="stringlist">string</param>

       /// <returns>result list</returns>

       private List<Dictionary<string, object>> ReadStringListByReader(DbDataReader reader, List<string> stringlist)

       {

           var listResult = new List<Dictionary<string, object>>();

           using (reader)

           {

               while (reader.Read())

               {

                   var dicResult = new Dictionary<string, object>();

                   foreach (var key in stringlist)

                   {

                       if (!stringlist.Exists(fileName => string.Compare(fileName, key, StringComparison.OrdinalIgnoreCase) == 0))

                           continue;

                       object obj;

                       try

                       {

                           obj = reader[key];

                       }

                       catch (Exception)

                       {

                           continue;

                       }

                       if (obj == DBNull.Value || obj == null)

                           continue;

                       dicResult.Add(key, obj);

                   }

                   listResult.Add(dicResult);

               }

           }

           return listResult;

       }

       /// <summary>

       /// Execute scalar by store procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">store procedure</param>

       /// <paramname="parameters">parameter list</param>

       /// <returns>return value</returns>

       private object ExecuteScalar(string cmdText, List<DbParameter> parameters)

       {

           using (var conn = GetConnection(ConnectionString))

           {

               conn.Open();

               using (var command = conn.CreateCommand())

               {

                   PrepareCommand(command, conn, cmdText, parameters);

                   return command.ExecuteScalar();

               }

           }

       }

       /// <summary>

       /// Prepare the execute command

       /// </summary>

       /// <paramname="cmd">my sql command</param>

       /// <paramname="conn">my sql connection</param>

       /// <paramname="cmdText">stored procedure</param>

       /// <paramname="parameters">parameter list</param>

       private void PrepareCommand(DbCommand cmd, DbConnection conn, string cmdText, List<DbParameter> parameters)

       {

           if (conn.State != ConnectionState.Open)

               conn.Open();

           cmd.Parameters.Clear();

           cmd.Connection = conn;

           cmd.CommandText = cmdText;

           cmd.CommandType = CommandType.Text;

           cmd.CommandTimeout = 30;

           if (parameters != null)

               foreach (var parameter in parameters)

               {

                   cmd.Parameters.Add(parameter);

               }

       }

       #endregion

       #region Public Property

       public int MaxConnectionCount

       {

           get

           {

               if (_maxConnectionCount <= 0)

                   _maxConnectionCount = 100;

               return _maxConnectionCount;

           }

           set { _maxConnectionCount = value; }

       }

       public abstract SqlSourceType DataSqlSourceType { get; }

       #endregion

       #region Protected Method

       protected abstract DbDataAdapter GetDataAdapter(DbCommand command);

       protected abstract DbConnection GetConnection(string connectionString);

       #endregion

       #region Public Methods

       /// <summary>

       /// Gets the connection string

       /// </summary>

       public string ConnectionString

       {

           get

           {

               if (_connectionString == null)

                   _connectionString = ConfigurationManager.ConnectionStrings[""].ConnectionString;

               return _connectionString;

           }

           set { _connectionString = value; }

       }

       /// <summary>

       /// Execute query by stored procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">stored procedure and parameter list</param>

       /// <returns>DataSet</returns>

       public DataSet ExecuteQuery(string cmdText)

       {

           try

           {

               AddConnection();

               return ExecuteQuery(cmdText, new List<DbParameter>());

           }

           finally

           {

               RemoveConnection();

           }

       }

       /// <summary>

       /// Execute non query by stored procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">stored procedure</param>

       /// <returns>execute count</returns>

       public int ExecuteNonQuery(string cmdText)

       {

           try

           {

               AddConnection();

               return ExecuteNonQuery(cmdText, new List<DbParameter>());

           }

           finally

           {

               RemoveConnection();

           }

       }

       /// <summary>

       /// Execute scalar by store procedure and parameter list

       /// </summary>

       /// <paramname="cmdText">store procedure</param>

       /// <returns>return value</returns>

       public object ExecuteScalar(string cmdText)

       {

           try

           {

               AddConnection();

               return ExecuteScalar(cmdText, new List<DbParameter>());

           }

           finally

           {

               RemoveConnection();

           }

       }

       /// <summary>

       /// Get data base parameter by parameter name and parameter value

       /// </summary>

       /// <paramname="key">parameter name</param>

       /// <paramname="value">parameter value</param>

       /// <returns>my sql parameter</returns>

       public abstract DbParameter GetDbParameter(string key, object value);

       /// <summary>

       /// Get data base parameter by parameter name and parameter value

       /// and parameter direction

       /// </summary>

       /// <paramname="key">parameter name</param>

       /// <paramname="value">parameter value</param>

       /// <paramname="direction">parameter direction </param>

       /// <returns>data base parameter</returns>

       public DbParameter GetDbParameter(string key, object value, ParameterDirection direction)

       {

           var parameter = GetDbParameter(key, value);

           parameter.Direction = direction;

           return parameter;

       }

       /// <summary>

       /// Get Dictionary list by string list

       /// </summary>

       /// <paramname="cmdText">Store procedure</param>

       /// <paramname="stringlist">string list</param>

       /// <returns>result list</returns>

       public List<Dictionary<string, object>> GetDictionaryList(string cmdText, List<string> stringlist)

       {

           return GetDictionaryList(cmdText, new List<DbParameter>(), stringlist);

       }

       /// <summary>

       /// Execute reader by store procedure

       /// </summary>

       /// <paramname="cmdText">store procedure</param>

       /// <returns>data reader</returns>

       public List<T> ReadEntityList<T>(string cmdText) where T : new()

       {

           try

           {

               AddConnection();

               return ReadEntityList<T>(cmdText, new List<DbParameter>());

           }

           finally

           {

               RemoveConnection();

           }

       }

       #endregion

    }

}

再创建MSSqlHelp 类：

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/********************************************************************************

** Class Name:   MySqlHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     MySqlHelp class

*********************************************************************************/

namespace BlogDBHelp

{

    using System.Data.Common;

    using System.Data.SqlClient;

    public class MSSqlHelp : AbstractDBHelp

    {

        #region Protected Method

        protected override DbDataAdapter GetDataAdapter(DbCommand command)

        {

           return new SqlDataAdapter(command as SqlCommand);

        }

        protected override DbConnection GetConnection(string connectionString)

        {

           return new SqlConnection(connectionString);

        }

        #endregion

        #region Public Mehtod

        public override SqlSourceType DataSqlSourceType

        {

           get { return SqlSourceType.MSSql; }

        }

        public override DbParameter GetDbParameter(string key, object value)

        {

           return new SqlParameter(key, value);

        }

        #endregion

    }

}

再创建MySqlHelp类

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/********************************************************************************

** Class Name:   MySqlHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     MySqlHelp class

*********************************************************************************/

namespace BlogDBHelp

{

    using System.Data.Common;

    using MySql.Data.MySqlClient;

    public class MySqlHelp : AbstractDBHelp

    {

        #region Protected Method

        protected override DbDataAdapter GetDataAdapter(DbCommand command)

        {

           return new MySqlDataAdapter();

        }

        protected override DbConnection GetConnection(string connectionString)

        {

           return new MySqlConnection(connectionString);

        }

        #endregion

        #region Public Mehtod

        public override DbParameter GetDbParameter(string key, object value)

        {

           return new MySqlParameter(key, value);

        }

        public override SqlSourceType DataSqlSourceType

        {

           get { return SqlSourceType.MySql; }

        }

        #endregion

    }

}

再创建OracleHelp类：

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/********************************************************************************

** Class Name:   OracleHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     OracleHelp class

*********************************************************************************/

namespace BlogDBHelp

{

    using System.Data.Common;

    using Oracle.DataAccess.Client;

    public class OracleHelp : AbstractDBHelp

    {

        #region Protected Method

        protected override DbDataAdapter GetDataAdapter(DbCommand command)

        {

           return new OracleDataAdapter(command as OracleCommand);

        }

        protected override DbConnection GetConnection(string connectionString)

        {

           return new OracleConnection(connectionString);

        }

        #endregion

        #region Public Mehtod

        public override DbParameter GetDbParameter(string key, object value)

        {

           return new OracleParameter(key, value);

        }

        public override SqlSourceType DataSqlSourceType

        {

           get { return SqlSourceType.Oracle; }

        }

        #endregion

    }

}

再创建SQLiteHelp类：

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/********************************************************************************

** Class Name:   SQLiteHelp

** Author：      Spring Yang

** Create date： 2013-3-16

** Modify：      Spring Yang

** Modify Date： 2013-3-16

** Summary：     SQLiteHelp class

*********************************************************************************/

namespace BlogDBHelp

{

    using System.Data.Common;

    using System.Data.SQLite;

    public class SQLiteHelp : AbstractDBHelp

    {

        #region Protected Method

        protected override DbDataAdapter GetDataAdapter(DbCommand command)

        {

           return new SQLiteDataAdapter(command as SQLiteCommand);

        }

        protected override DbConnection GetConnection(string connectionString)

        {

           return new SQLiteConnection(connectionString);

        }

        #endregion

        #region Public Mehtod

        public override DbParameter GetDbParameter(string key, object value)

        {

           return new SQLiteParameter(key, value);

        }

        public override SqlSourceType DataSqlSourceType

        {

           get { return SqlSourceType.SQLite; }

        }

        #endregion

    }

}

仔细观察上面代码，发现每增加一种数据库的支持，我们只需实现几个特有抽象方法就可以了，而调用只需像如下就可以了。

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IDBHelp　 _dbHelpInstance = new SQLiteHelp

                   {

                       ConnectionString ="";    };

欢迎各位参与讨论，如果觉得对你有帮助，请点击    推荐下，万分谢谢.

作者：spring yang

出处：http://www.cnblogs.com/springyangwc/

本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。