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
    }
}

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;
        }
    }
}

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);
    }
}

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
    }
}

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);
            }
        }
    }
}

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>

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();
        }
    }
}

 

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。