继承IDbConnection连接不同数据库

 

本方案可实现仅修改app.config即可连接不同数据库，但是设计数据库时需要注意各种数据库的数据类型是不一样的。

各种不同数据库的Connection、Command、DataAdapter、Transaction和Parameter都继承自IDbConnection、IDbCommand、IDbDataAdapter、IDbTransaction和IDbDataParameter，用一个工厂来实现接口的实例即可实现连接不同数据库。

首先，需要新建一个类库，命名为DbManager，此类库需要5个文件， 

1、创建一个枚举类型：DataProvider.cs

namespace DbManager

{ 

    public enum DataProvider
    {
        Oracle,
        SqlServer,
        OleDb,
        Odbc,
        MySql
    }
}

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2、创建一个工厂类，用来产生以上不同数据库的实例：DBManagerFactory.cs

using  System.Data;
using  System.Data.Odbc;
using  System.Data.SqlClient;
using  System.Data.OleDb;
using  System.Data.OracleClient; //需要添加引用
using  MySql.Data.MySqlClient;   //请自行安装MySQLConnector/Net后添加引用

namespace  DbManager
{
     public   sealed   class  DBManagerFactory
    {
         private  DBManagerFactory()
        {
        }

         public   static  IDbConnection GetConnection(DataProvider providerType)
        {
            IDbConnection iDbConnection;
             switch  (providerType)
            {
                 case  DataProvider.SqlServer:
                    iDbConnection  =   new  SqlConnection();
                     break ;
                 case  DataProvider.OleDb:
                    iDbConnection  =   new  OleDbConnection();
                     break ;
                 case  DataProvider.Odbc:
                    iDbConnection  =   new  OdbcConnection();
                     break ;
                 case  DataProvider.Oracle:
                    iDbConnection  =   new  OracleConnection();
                     break ;
                 case  DataProvider.MySql:
                    iDbConnection  =   new  MySqlConnection();
                     break ;
                 default :
                     return   null ;
            }
             return  iDbConnection;
        }

         public   static  IDbCommand GetCommand(DataProvider providerType)
        {
             switch  (providerType)
            {
                 case  DataProvider.SqlServer:
                     return   new  SqlCommand();
                 case  DataProvider.OleDb:
                     return   new  OleDbCommand();
                 case  DataProvider.Odbc:
                     return   new  OdbcCommand();
                 case  DataProvider.Oracle:
                     return   new  OracleCommand();
                 case  DataProvider.MySql:
                     return   new  MySqlCommand();
                 default :
                     return   null ;
            }
        }

         public   static  IDbDataAdapter GetDataAdapter(DataProvider providerType)
        {
             switch  (providerType)
            {
                 case  DataProvider.SqlServer:
                     return   new  SqlDataAdapter();
                 case  DataProvider.OleDb:
                     return   new  OleDbDataAdapter();
                 case  DataProvider.Odbc:
                     return   new  OdbcDataAdapter();
                 case  DataProvider.Oracle:
                     return   new  OracleDataAdapter();
                 case  DataProvider.MySql:
                     return   new  MySqlDataAdapter();
                 default :
                     return   null ;
            }
        }

         public   static  IDbTransaction GetTransaction(DataProvider providerType)
        {
            IDbConnection iDbConnection  =  GetConnection(providerType);
            IDbTransaction iDbTransaction  =  iDbConnection.BeginTransaction();
             return  iDbTransaction;
        }

         public   static  IDbDataParameter[] GetParameters(DataProvider providerType,  int  paramsCount)
        {
            IDbDataParameter[] idbParams  =   new  IDbDataParameter[paramsCount];
             switch  (providerType)
            {
                 case  DataProvider.SqlServer:
                     for  ( int  i  =   0 ; i  <  paramsCount; i ++ )
                    {
                        idbParams[i]  =   new  SqlParameter();
                    }
                     break ;
                 case  DataProvider.OleDb:
                     for  ( int  i  =   0 ; i  <  paramsCount; i ++ )
                    {
                        idbParams[i]  =   new  OleDbParameter();
                    }
                     break ;
                 case  DataProvider.Odbc:
                     for  ( int  i  =   0 ; i  <  paramsCount; i ++ )
                    {
                        idbParams[i]  =   new  OdbcParameter();
                    }
                     break ;
                 case  DataProvider.Oracle:
                     for  ( int  i  =   0 ; i  <  paramsCount; i ++ )
                    {
                        idbParams[i]  =   new  OracleParameter();
                    }
                     break ;
                 case  DataProvider.MySql:
                     for  ( int  i  =   0 ; i  <  paramsCount; i ++ )
                    {
                        idbParams[i]  =   new  MySqlParameter();
                    }
                     break ;
                 default :
                    idbParams  =   null ;
                     break ;
            }
             return  idbParams;
        }
    }
}

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3、创建一个接口：IDBManager.cs

using  System.Data;

namespace  DbManager
{
     public   interface  IDBManager
    {
        DataProvider ProviderType
        {
             get ;
             set ;
        }

        IDbConnection Connection
        {
             get ;
             set ;
        }

        IDataReader DataReader
        {
             get ;
             set ;
        }

        IDbCommand Command
        {
             get ;
             set ;
        }

        IDbTransaction Transaction
        {
             get ;
             set ;
        }

        IDbDataParameter[] Parameters
        {
             get ;
             set ;
        }

         string  ConnectionString
        {
             get ;
             set ;
        }

         void  Open();
         void  Close();
         void  Dispose();
         void  CreateParameters( int  paramsCount);
         void  AddParameters( int  index,  string  paramName,  object  objValue);
         void  BeginTransaction();
         void  CommitTransaction();
         void  CloseReader();
        IDataReader ExecuteReader(CommandType commandType,  string  commandText);
         int  ExecuteNonQuery(CommandType commandType,  string  commandText);
         object  ExecuteScalar(CommandType commandType,  string  commandText);
        DataSet ExecuteDataSet(CommandType commandType,  string  commandText);
    }
}

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4、创建一个类来实现IDBManager接口：DBManager.cs

using  System;
using  System.Data;

namespace  DbManager
{
     public   sealed   class  DBManager : IDBManager, IDisposable
    {
         #region  字段

         private  DataProvider _providerType;
         private  IDbConnection _idbConnection;
         private  IDataReader _iDataReader;
         private  IDbCommand _idbCommand;
         private  IDbTransaction _idbTransaction;
         private  IDbDataParameter[] _idbParameters;
         private   string  _connectionString;

         #endregion

         #region  构造方法

         public  DBManager()
        {
        }

         public  DBManager(DataProvider providerType)
        {
            ProviderType  =  providerType;
        }

         public  DBManager(DataProvider providerType,  string  connectionString)
        {
            ProviderType  =  providerType;
            ConnectionString  =  connectionString;
        }

         #endregion

         #region  属性

         public  DataProvider ProviderType
        {
             get  {  return  _providerType; }
             set  { _providerType  =  value; }
        }

         public  IDbConnection Connection
        {
             get  {  return  _idbConnection; }
             set  { _idbConnection  =  value; }
        }

         public  IDataReader DataReader
        {
             get  {  return  _iDataReader; }
             set  { _iDataReader  =  value; }
        }

         public  IDbCommand Command
        {
             get  {  return  _idbCommand; }
             set  { _idbCommand  =  value; }
        }

         public  IDbTransaction Transaction
        {
             get  {  return  _idbTransaction; }
             set  { _idbTransaction  =  value; }
        }

         public  IDbDataParameter[] Parameters
        {
             get  {  return  _idbParameters; }
             set  { _idbParameters  =  value; }
        }

         public   string  ConnectionString
        {
             get  {  return  _connectionString; }
             set  { _connectionString  =  value; }
        }

         #endregion

         #region  公有方法

         public   void  Open()
        {
            Connection  =  DBManagerFactory.GetConnection(ProviderType);
            Connection.ConnectionString  =  ConnectionString;
             if  (Connection.State  !=  ConnectionState.Open)
            {
                Connection.Open();
            }
            Command  =  DBManagerFactory.GetCommand(ProviderType);
        }

         public   void  Close()
        {
             if  (Connection.State  !=  ConnectionState.Closed)
            {
                Connection.Close();
            }
        }

         public   void  Dispose()
        {
            GC.SuppressFinalize( this );
            Close();
            Command  =   null ;
            Transaction  =   null ;
            Connection  =   null ;
        }

         public   void  CreateParameters( int  paramsCount)
        {
            Parameters  =   new  IDbDataParameter[paramsCount];
            Parameters  =  DBManagerFactory.GetParameters(ProviderType, paramsCount);
        }

         public   void  AddParameters( int  index,  string  paramName,  object  objValue)
        {
             if  (index  <  Parameters.Length)
            {
                Parameters[index].ParameterName  =  paramName;
                Parameters[index].Value  =  objValue;
            }
        }

         public   void  BeginTransaction()
        {
             if  (Transaction  ==   null )
            {
                Transaction  =  DBManagerFactory.GetTransaction(ProviderType);
            }
            Command.Transaction  =  Transaction;
        }

         public   void  CommitTransaction()
        {
             if  (Transaction  !=   null )
            {
                Transaction.Commit();
            }
            Transaction  =   null ;
        }

         public   void  CloseReader()
        {
             if  (DataReader  !=   null )
            {
                DataReader.Close();
            }
        }

         public  IDataReader ExecuteReader(CommandType commandType,  string  commandText)
        {
            Command  =  DBManagerFactory.GetCommand(ProviderType);
            Command.Connection  =  Connection;
            PrepareCommand(Command, Connection, Transaction, commandType, commandText, Parameters);
            DataReader  =  Command.ExecuteReader();
            Command.Parameters.Clear();
             return  DataReader;
        }

         public   int  ExecuteNonQuery(CommandType commandType,  string  commandText)
        {
            Command  =  DBManagerFactory.GetCommand(ProviderType);
            PrepareCommand(Command, Connection, Transaction, commandType, commandText, Parameters);
             int  returnValue  =  Command.ExecuteNonQuery();
            Command.Parameters.Clear();
             return  returnValue;
        }

         public   object  ExecuteScalar(CommandType commandType,  string  commandText)
        {
            Command  =  DBManagerFactory.GetCommand(ProviderType);
            PrepareCommand(Command, Connection, Transaction, commandType, commandText, Parameters);
             object  returnValue  =  Command.ExecuteScalar();
            Command.Parameters.Clear();
             return  returnValue;
        }

         public  DataSet ExecuteDataSet(CommandType commandType,  string  commandText)
        {
            Command  =  DBManagerFactory.GetCommand(ProviderType);
            PrepareCommand(Command, Connection, Transaction, commandType, commandText, Parameters);
            IDbDataAdapter dataAdapter  =  DBManagerFactory.GetDataAdapter(ProviderType);
            dataAdapter.SelectCommand  =  Command;
            DataSet dataSet  =   new  DataSet();
            dataAdapter.Fill(dataSet);
            Command.Parameters.Clear();
             return  dataSet;
        }

         #endregion

         #region  私有方法

         private   void  AttachParameters(IDbCommand command, IDbDataParameter[] commandParameters)
        {
             foreach  (IDbDataParameter idbParameter  in  commandParameters)
            {
                 if  (idbParameter.Direction  ==  ParameterDirection.InputOutput  &&  idbParameter.Value  ==   null )
                {
                    idbParameter.Value  =  DBNull.Value;
                }
                command.Parameters.Add(idbParameter);
            }
        }

         private   void  PrepareCommand(IDbCommand command, IDbConnection connection, IDbTransaction transaction,
                                    CommandType commandType,  string  commandText, IDbDataParameter[] commandParameters)
        {
            command.Connection  =  connection;
            command.CommandText  =  commandText;
            command.CommandType  =  commandType;
             if  (transaction  !=   null )
            {
                command.Transaction  =  transaction;
            }
             if  (commandParameters  !=   null )
            {
                AttachParameters(command, commandParameters);
            }
        }

         #endregion
    }
}

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5、再加一个DBHelper.cs，来调用DBManager类，外部来直接调用DBHelper类即可。

using  System;
using  System.Data;
using  System.Configuration;

namespace   DbManager
{
     public   class  DBHelper
    {
         private   static   readonly  IDBManager dbManager  =   new  DBManager(GetDataProvider(), GetConnectionString());

         ///   <summary>
         ///  从配置文件中选择数据库类型
         ///   </summary>
         ///   <returns> DataProvider枚举值 </returns>
         private   static  DataProvider GetDataProvider()
        {
             string  providerType  =  ConfigurationManager.AppSettings[ " DataProvider " ];
            DataProvider dataProvider;
             switch  (providerType)
            {
                 case   " Oracle " :
                    dataProvider  =  DataProvider.Oracle;
                     break ;
                 case   " SqlServer " :
                    dataProvider  =  DataProvider.SqlServer;
                     break ;
                 case   " OleDb " :
                    dataProvider  =  DataProvider.OleDb;
                     break ;
                 case   " Odbc " :
                    dataProvider  =  DataProvider.Odbc;
                     break ;
                 case   " MySql " :
                    dataProvider  =  DataProvider.MySql;
                     break ;
                 default :
                     return  DataProvider.Odbc;
            }
             return  dataProvider;
        }

         ///   <summary>
         ///  从配置文件获取连接字符串
         ///   </summary>
         ///   <returns> 连接字符串 </returns>
         private   static   string  GetConnectionString()
        {
             return  ConfigurationManager.ConnectionStrings[ " ConnString " ].ConnectionString;
        }

         ///   <summary>
         ///  关闭数据库连接的方法
         ///   </summary>
         public   static   void  Close()
        {
            dbManager.Dispose();
        }

         ///   <summary>
         ///  创建参数
         ///   </summary>
         ///   <param name="paramsCount"> 参数个数 </param>
         public   static   void  CreateParameters( int  paramsCount)
        {
            dbManager.CreateParameters(paramsCount);
        }

         ///   <summary>
         ///  添加参数
         ///   </summary>
         ///   <param name="index"> 参数索引 </param>
         ///   <param name="paramName"> 参数名 </param>
         ///   <param name="objValue"> 参数值 </param>
         public   static   void  AddParameters( int  index,  string  paramName,  object  objValue)
        {
            dbManager.AddParameters(index, paramName, objValue);
        }

         ///   <summary>
         ///  执行增删改
         ///   </summary>
         ///   <param name="sqlString"> 安全的sql语句string.Format() </param>
         ///   <returns> 操作成功返回true </returns>
         public   static   bool  ExecuteNonQuery( string  sqlString)
        {
             try
            {
                dbManager.Open();
                 return  dbManager.ExecuteNonQuery(CommandType.Text, sqlString)  >   0   ?   true  :  false ;
            }
             catch  (Exception e)
            {
                 throw   new  Exception(e.Message);
            }
             finally
            {
                dbManager.Dispose();
            }
        }

         ///   <summary>
         ///  执行查询
         ///   </summary>
         ///   <param name="sqlString"> 安全的sql语句string.Format() </param>
         ///   <returns> 返回IDataReader </returns>
         public   static  IDataReader ExecuteReader( string  sqlString)
        {
             try
            {
                dbManager.Open();
                 return  dbManager.ExecuteReader(CommandType.Text, sqlString);
            }
             catch  (Exception e)
            {
                 throw   new  Exception(e.Message);
            }
        }
    }
}

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现在，将上述项目生成一个DbManager.dll类库，在具体的DAL层里面就可以直接调用了。

DBHelper类没有全部写完，只写了ExecuteNonQuery()和ExecuteReader()两个方法，对于有参和无参的增删改查操作暂时够用，返回DataSet的方法未写，Transaction相关的也未写。

6、app.config

<? xml version = " 1.0 "  encoding = " utf-8 "   ?>
< configuration >
     < connectionStrings >
         < add name = " ConnString "  connectionString = " server=localhost;database=yourDbName;Persist Security Info=False;uid=root;pwd=mysqladmin " />
         <!--  通过改变ConnectionString的值来更换数据库连接字符串
         < add name = " ConnString "  connectionString = " Provider=Microsoft.Jet.OLEDB.4.0;Data Source=DBDemo.mdb;Jet OLEDB:Database Password=1234 " />
         < add name = " ConnString "  connectionString = " server=localhost;database=yourDbName;Persist Security Info=False;Integrated Security=SSPI " />
         < add name = " ConnString "  connectionString = " server=localhost;database= yourDbName ;Persist Security Info=False;uid=sa;pwd= 1234" />
         < add name = " ConnString "  connectionString = " server=localhost;database= yourDbName ;Persist Security Info=False;uid=root;pwd=mysqladmin " />
         -->
     </ connectionStrings >
     < appSettings >
         < add key = " DataProvider "  value = " MySql " />
         <!--  通过改变value值来更换数据库
         < add key = " DataProvider "  value = " Oracle " />
         < add key = " DataProvider "  value = " SqlServer " />
         < add key = " DataProvider "  value = " OleDb " />
         < add key = " DataProvider "  value = " Odbc " />  
         < add key = " DataProvider "  value = " MySql " />
         -->
     </ appSettings >
</ configuration >

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7、程序中的调用

举个简单的例子，我们就创建一个控制台应用程序，然后添加DbManager.dll的引用

Program.cs文件的样子：

using  System;
using  System.Data;
using  DbManager;  //记得引入命名空间

namespace  DBDemo
{
     class  Program
    {
         static   void  Main( string [] args)
        {
            SelectWithoutParams();
            Console.WriteLine( " ------安全sql语句string.Format()的查询结果------ " );
            SelectWithSafeSql( 4 );
            Console.WriteLine( " ------参数化语句的查询结果------- " );
            SelectWithParams( " 总统套间 " );

        }

 

        private static void SelectWithoutParams()

        {
             const   string  sql  =   " select * from RoomType " ;
            IDataReader reader  =  DBHelper.ExecuteReader(sql);
             while  (reader.Read())
            {
                Console.WriteLine(reader[ " TypeName " ].ToString());
            }
            DBHelper.Close();  //记得关闭reader
        }

         private   static   void  SelectWithSafeSql( int  TypeId)
        {
             string  sql  =   string .Format( " select * from RoomType where TypeId={0} " , TypeId);
            IDataReader reader  =  DBHelper.ExecuteReader(sql);
             while  (reader.Read())
            {
                Console.WriteLine(reader[ " TypeName " ].ToString());
            }
            DBHelper.Close();
        }

         private   static   void  SelectWithParams( string  typeName)
        {

            string sql = "select * from RoomType where TypeName=@TypeName";

 

            //先创建参数，然后才能添加参数 

            DBHelper.CreateParameters( 1 );   // 参数个数，1个
            DBHelper.AddParameters( 0 ,  " @TypeName " , typeName);
            IDataReader reader  =  DBHelper.ExecuteReader(sql);
             while  (reader.Read())
            {
                Console.WriteLine(reader[ " TypeName " ].ToString());
            }
            DBHelper.Close();
        }
    }
}

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OK！全部完成！在具体的DAL层中，调用DBHelper的相关方法即可，如果是查询方法，记得最后要写关闭代码。只要表结构一样，可以在app.config中随意切换数据库。

最后注意的是：

各个数据库的插入语句不一样，假设我们有4个字段，第一个字段fieldName1为自增字段。

对于SQLServer，不需要写自增字段，

语句是：INSERT INTO table VALUES(value2, value3, value4);

对于MySQL，自增字段位置需要写null代替，

语句是：INSERT INTO table VALUES(NULL, value2, value3, value4);

而对于ACCESS数据库，则必须写完整，

语句是：INSERT INTO table(fieldName2, fieldName3,fieldName4) VALUES(value2, value3, value4);

为了实现兼容，大家还是都按完整的来写，就不会有错了