策略模式实现支持多种类数据库的DBHelp

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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