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 >         /// < param name = "cmdText" >stored procedure</ param >         /// < returns >DataSet</ returns >         DataSet ExecuteQuery(string cmdText);         /// < summary >         /// Execute non query by stored procedure and parameter list         /// </ summary >         /// < param name = "cmdText" >stored procedure</ param >         /// < returns >execute count</ returns >         int ExecuteNonQuery(string cmdText);         /// < summary >         /// Execute scalar by store procedure         /// </ summary >         /// < param name = "cmdText" >store procedure</ param >         /// < returns >return value</ returns >         object ExecuteScalar(string cmdText);         /// < summary >         /// Get data base parameter by parameter name and parameter value         /// </ summary >         /// < param name = "key" >parameter name</ param >         /// < param name = "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 >         /// < param name = "key" >parameter name</ param >         /// < param name = "value" >parameter value</ param >         /// < param name = "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 >         /// < typeparam name = "T" >entity</ typeparam >         /// < param name = "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 >         /// < param name = "cmdText" >store procedure</ param >         /// < param name = "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 >         /// < param name = "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 >         /// < param name = "cmdText" >stored procedure and parameter list</ param >         /// < param name = "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 >         /// < param name = "cmdText" >stored procedure</ param >         /// < param name = "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 >         /// < param name = "cmdText" >store procedure</ param >         /// < param name = "parameters" >parameter list</ param >         /// < param name = "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 >         /// < param name = "cmdText" >store procedure</ param >         /// < param name = "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 >         /// < typeparam name = "T" >entity</ typeparam >         /// < param name = "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));                     }                     var inst = new T();                     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 >         /// < param name = "cmdText" >Store procedure</ param >         /// < param name = "parameters" >parameter list</ param >         /// < param name = "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 >         /// < param name = "reader" >Db data reader</ param >         /// < param name = "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 >         /// < param name = "cmdText" >store procedure</ param >         /// < param name = "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 >         /// < param name = "cmd" >my sql command</ param >         /// < param name = "conn" >my sql connection</ param >         /// < param name = "cmdText" >stored procedure</ param >         /// < param name = "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 >         /// < param name = "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 >         /// < param name = "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 >         /// < param name = "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 >         /// < param name = "key" >parameter name</ param >         /// < param name = "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 >         /// < param name = "key" >parameter name</ param >         /// < param name = "value" >parameter value</ param >         /// < param name = "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 >         /// < param name = "cmdText" >Store procedure</ param >         /// < param name = "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 >         /// < param name = "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/

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