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：

/********************************************************************************
** 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：

/********************************************************************************
** 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：

/********************************************************************************
** 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 Propertyprivate static int _currentCount;private int _maxConnectionCount;private string _connectionString;#endregion#region Private Methodsprivate 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);elsepi.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 Propertypublic int MaxConnectionCount{get{if (_maxConnectionCount <= 0)_maxConnectionCount = 100;return _maxConnectionCount;}set { _maxConnectionCount = value; }}public abstract SqlSourceType DataSqlSourceType { get; }#endregion#region Protected Methodprotected 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：

/********************************************************************************
** 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 Methodprotected override DbDataAdapter GetDataAdapter(DbCommand command){return new SqlDataAdapter(command as SqlCommand);}protected override DbConnection GetConnection(string connectionString){return new SqlConnection(connectionString);}#endregion#region Public Mehtodpublic 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

/********************************************************************************
** 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 Methodprotected override DbDataAdapter GetDataAdapter(DbCommand command){return new MySqlDataAdapter();}protected override DbConnection GetConnection(string connectionString){return new MySqlConnection(connectionString);}#endregion#region Public Mehtodpublic 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：

/********************************************************************************
** 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 Methodprotected override DbDataAdapter GetDataAdapter(DbCommand command){return new OracleDataAdapter(command as OracleCommand);}protected override DbConnection GetConnection(string connectionString){return new OracleConnection(connectionString);}#endregion#region Public Mehtodpublic 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：

/********************************************************************************
** 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 Methodprotected override DbDataAdapter GetDataAdapter(DbCommand command){return new SQLiteDataAdapter(command as SQLiteCommand);}protected override DbConnection GetConnection(string connectionString){return new SQLiteConnection(connectionString);}#endregion#region Public Mehtodpublic 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。

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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