DBHelper (支持事务与数据库变更） z

using System;
using System.Data;
using System.Data.Common;
using Project.BaseFramework;
using System.Collections.Generic;
using System.Configuration;

namespace Project.BaseFramework.DataProvider
{
    public class DBHelper
    {

        #region Constuctor
        public DBHelper() { }

        private static string ConnectionString = ConfigurationManager.AppSettings["DBConnectionString"];

        private static IDBClient DBClient = DBClientFactory.GetDBClient(ConfigurationManager.AppSettings["DBClient"]);

        [ThreadStatic]
        private static TransConnection TransConnectionObj = null;

        #endregion

        #region ExecuteNonQuery
        public static int ExecuteNonQuery(CommandType cmdType, string cmdText, params DbParameter[] parameterValues)
        {
            int result = 0;
            bool mustCloseConn = true;

            DbCommand cmd = PrepareCmd(cmdType, cmdText, parameterValues, out mustCloseConn);
            OpenConn(cmd.Connection);
            result = cmd.ExecuteNonQuery();

            if (mustCloseConn) CloseConn(cmd.Connection);
            ClearCmdParameters(cmd);
            cmd.Dispose();

            return result;
        }

        #endregion ExecuteNonQuery

        #region ExecuteScalar
        public static object ExecuteScalar(CommandType cmdType, string cmdText, params DbParameter[] parameterValues)
        {
            object result = 0;
            bool mustCloseConn = true;

            DbCommand cmd = PrepareCmd(cmdType, cmdText, parameterValues, out mustCloseConn);
            OpenConn(cmd.Connection);
            result = cmd.ExecuteScalar();

            if (mustCloseConn) CloseConn(cmd.Connection);
            ClearCmdParameters(cmd);
            cmd.Dispose();

            return result;
        }
        #endregion ExecuteScalar

        #region ExecuteReader
        public static DbDataReader ExecuteReader(CommandType cmdType, string cmdText, params DbParameter[] parameterValues)
        {
            DbDataReader result = null;
            bool mustCloseConn = true;
            DbCommand cmd = PrepareCmd(cmdType, cmdText, parameterValues, out mustCloseConn);
            try
            {
                OpenConn(cmd.Connection);
                if (mustCloseConn)
                {
                    result = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                }
                else
                {
                    result = cmd.ExecuteReader();
                }
                ClearCmdParameters(cmd);
                return result;
            }
            catch (Exception ex)
            {
                if (mustCloseConn) CloseConn(cmd.Connection);
                ClearCmdParameters(cmd);
                cmd.Dispose();
                throw ;
            }
        }
        #endregion ExecuteReader

        #region ExecuteDataset
        public static DataSet ExecuteDataSet(CommandType cmdType, string cmdText, params DbParameter[] parameterValues)
        {
            DataSet result = null;
            bool mustCloseConn = true;

            DbCommand cmd = PrepareCmd(cmdType, cmdText, parameterValues, out mustCloseConn);
            using (DbDataAdapter da = DBClient.GetDbDataAdappter())
            {
                da.SelectCommand = cmd;
                result = new DataSet();

                da.Fill(result);
            }

            if (mustCloseConn) CloseConn(cmd.Connection);
            ClearCmdParameters(cmd);
            cmd.Dispose();

            return result;
        }
        #endregion ExecuteDataset

        #region ExecuteDataTable
        public static DataTable ExecuteDataTable(CommandType cmdType, string cmdText, params DbParameter[] parameterValues)
        {
            DataSet ds = ExecuteDataSet(cmdType,cmdText, parameterValues);
            if (ds != null && ds.Tables.Count > 0)
                return ds.Tables[0];
            else
                return null;
        }
        #endregion

        #region Transaction
        public static void BeginTransaction()
        {
            if (TransConnectionObj == null)
            {
                DbConnection conn = DBClient.GetDbConnection(ConnectionString);
                OpenConn(conn);
                DbTransaction trans = conn.BeginTransaction();
                TransConnectionObj = new TransConnection();
                TransConnectionObj.DBTransaction = trans;
            }
            else
            {
                TransConnectionObj.Deeps += 1;
            }
        }

        public static void CommitTransaction()
        {
            if (TransConnectionObj == null) return;
            if (TransConnectionObj.Deeps > 0)
            {
                TransConnectionObj.Deeps -= 1;
            }
            else
            {
                TransConnectionObj.DBTransaction.Commit();
                ReleaseTransaction();
            }
        }

        public static void RollbackTransaction()
        {
            if (TransConnectionObj == null) return;
            if (TransConnectionObj.Deeps > 0)
            {
                TransConnectionObj.Deeps -= 1;
            }
            else
            {
                TransConnectionObj.DBTransaction.Rollback();
                ReleaseTransaction();
            }
        }

        private static void ReleaseTransaction()
        {
            if (TransConnectionObj == null) return;
            DbConnection conn = TransConnectionObj.DBTransaction.Connection;
            TransConnectionObj.DBTransaction.Dispose();
            TransConnectionObj = null;
            CloseConn(conn);
        }

        #endregion

        #region Connection
        private static void OpenConn(DbConnection conn)
        {
            if (conn == null) conn = DBClient.GetDbConnection(ConnectionString);
            if (conn.State == ConnectionState.Closed) conn.Open();
        }

        private static void CloseConn(DbConnection conn)
        {
            if (conn == null) return;
            if (conn.State == ConnectionState.Open) conn.Close();
            conn.Dispose();
            conn = null;
        }
        #endregion

        #region Create DbParameter

        public static DbParameter CreateInDbParameter(string paraName, DbType type, int size, object value)
        {
            return CreateDbParameter(paraName, type, size, value, ParameterDirection.Input);
        }

        public static DbParameter CreateInDbParameter(string paraName, DbType type, object value)
        {
            return CreateDbParameter(paraName, type, 0, value, ParameterDirection.Input);
        }

        public static DbParameter CreateOutDbParameter(string paraName, DbType type, int size)
        {
            return CreateDbParameter(paraName, type, size, null, ParameterDirection.Output);
        }

        public static DbParameter CreateOutDbParameter(string paraName, DbType type)
        {
            return CreateDbParameter(paraName, type, 0, null, ParameterDirection.Output);
        }

        public static DbParameter CreateReturnDbParameter(string paraName, DbType type, int size)
        {
            return CreateDbParameter(paraName, type, size, null, ParameterDirection.ReturnValue);
        }

        public static DbParameter CreateReturnDbParameter(string paraName, DbType type)
        {
            return CreateDbParameter(paraName, type, 0, null, ParameterDirection.ReturnValue);
        }

        public static DbParameter CreateDbParameter(string paraName, DbType type, int size, object value, ParameterDirection direction)
        {
            DbParameter para = DBClient.GetDbParameter();

            para.ParameterName = paraName;

            if (size != 0)
            {
                para.Size = size;
            }

            para.DbType = type;

            if (value != null)
            {
                para.Value = value;
            }
            else
            {
                para.Value = DBNull.Value;
            }

            para.Direction = direction;

            return para;
        }

        #endregion

        #region Command and Parameter
        /// <summary>
        /// 预处理用户提供的命令,数据库连接/事务/命令类型/参数
        /// </summary>
        /// <param>要处理的DbCommand</param>
        /// <param>数据库连接</param>
        /// <param>一个有效的事务或者是null值</param>
        /// <param>命令类型 (存储过程,命令文本, 其它.)</param>
        /// <param>存储过程名或都T-SQL命令文本</param>
        /// <param>和命令相关联的DbParameter参数数组,如果没有参数为'null'</param>
        /// <param><c>true</c> 如果连接是打开的,则为true,其它情况下为false.</param>
        private static DbCommand PrepareCmd(CommandType cmdType,string cmdText, DbParameter[] cmdParams, out bool mustCloseConn)
        {
            DbCommand cmd = DBClient.GetDbCommand(cmdText);

            DbConnection conn = null;
            if (TransConnectionObj != null)
            {
                conn = TransConnectionObj.DBTransaction.Connection;
                cmd.Transaction = TransConnectionObj.DBTransaction;
                mustCloseConn = false;
            }
            else
            {
                conn = DBClient.GetDbConnection(ConnectionString);
                mustCloseConn = true;
            }
            cmd.Connection = conn;

            cmd.CommandType = cmdType;

            AttachParameters(cmd, cmdParams);

            return cmd;
        }

        /// <summary>
        /// 将DbParameter参数数组(参数值)分配给DbCommand命令.
        /// 这个方法将给任何一个参数分配DBNull.Value;
        /// 该操作将阻止默认值的使用.
        /// </summary>
        /// <param>命令名</param>
        /// <param>SqlParameters数组</param>
        private static void AttachParameters(DbCommand command, DbParameter[] commandParameters)
        {
            if (command == null) throw new ArgumentNullException("command");
            if (commandParameters != null)
            {
                foreach (DbParameter p in commandParameters)
                {
                    if (p != null)
                    {
                        // 检查未分配值的输出参数,将其分配以DBNull.Value.
                        if ((p.Direction == ParameterDirection.InputOutput || p.Direction == ParameterDirection.Input) &&
                        (p.Value == null))
                        {
                            p.Value = DBNull.Value;
                        }
                        command.Parameters.Add(p);
                    }
                }
            }
        }

        private static void ClearCmdParameters(DbCommand cmd)
        {
            bool canClear = true;
            if (cmd.Connection != null && cmd.Connection.State != ConnectionState.Open)
            {
                foreach (DbParameter commandParameter in cmd.Parameters)
                {
                    if (commandParameter.Direction != ParameterDirection.Input)
                    {
                        canClear = false;
                        break;
                    }
                }
            }
            if (canClear)
            {
                cmd.Parameters.Clear();
            }
        }
        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;

namespace Project.BaseFramework.DataProvider
{
    internal class TransConnection
    {
        public TransConnection()
        {
            this.Deeps = 0;
        }

        public DbTransaction DBTransaction { get; set; }

        public int Deeps { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;
using System.Data.SqlClient;

namespace Project.BaseFramework.DataProvider
{
    public interface IDBClient
    {
        DbConnection GetDbConnection(string connectionString);

        DbCommand GetDbCommand(string cmdText);

        DbDataAdapter GetDbDataAdappter();

        DbParameter GetDbParameter();
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;
using System.Data.SqlClient;

namespace Project.BaseFramework.DataProvider
{
    public class SqlServerClient:IDBClient
    {
        public DbConnection GetDbConnection(string connectionString)
        {
            return new SqlConnection(connectionString);
        }

        public DbCommand GetDbCommand(string cmdText)
        {
            return new SqlCommand(cmdText);
        }

        public DbDataAdapter GetDbDataAdappter()
        {
            return new SqlDataAdapter();
        }

        public DbParameter GetDbParameter()
        {
            return new SqlParameter();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;
using MySql.Data.MySqlClient;

namespace Project.BaseFramework.DataProvider
{
    public class MySqlSqlClient:IDBClient
    {
        public DbConnection GetDbConnection(string connectionString)
        {
            return new MySqlConnection(connectionString);
        }

        public DbCommand GetDbCommand(string cmdText)
        {
            return new MySqlCommand(cmdText);
        }

        public DbDataAdapter GetDbDataAdappter()
        {
            return new MySqlDataAdapter();
        }

        public DbParameter GetDbParameter()
        {
            return new MySqlParameter();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Configuration;
using System.Reflection;

namespace Project.BaseFramework.DataProvider
{
    public class DBClientFactory
    {
        private static readonly string path = "Project.BaseFramework";

        public static IDBClient GetDBClient(string dbClientClassName)
        {
            if(string.IsNullOrEmpty(dbClientClassName))
                dbClientClassName="SqlServerClient";
            string className = string.Format("{0}.DataProvider.{1}", path, dbClientClassName);
            return (IDBClient)Assembly.Load(path).CreateInstance(className);
        }
    }
}

配置文件

<appSettings>
    <add key="DBConnectionString" value="Data Source=.;Initial Catalog=ProjectData;Persist Security Info=True;User ID=sa;Password=kjkj,911;"/>
    <add key="DBClient" value="SqlServerClient"/>
</appSettings>

单个事务操作示例

try
{
    DBHelper.BeginTransaction();
    // add
    DBHelper.ExecuteNonQuery(CommandType.Text, "INSERT INTO TRole(ID,RoleName) VALUES('R1','MKT')");

    //detele by pk
    DBHelper.ExecuteNonQuery(CommandType.Text, "DELETE FROM TRole WHERE ID='R1'");

    Console.WriteLine(string.Format("Success and Commited"));
    DBHelper.CommitTransaction();
}
catch (Exception ex)
{
    Console.WriteLine(string.Format("Exception and rollback"));
    DBHelper.RollbackTransaction();
}

用法是：只需要把相关联的代码放在BeginTransaction和CommitTransaction中间，如果发生异常调用RollbackTransaction即可。

实现事务的方法是：

首先，DBHelper维护一个TransConnection类型的字段，并添加ThreadStatic. ThreadStatic可以维护在线程级别上的唯一性。

[ThreadStatic]
private static TransConnection TransConnectionObj = null;

其次，TransConnection的作用是保存事务，并记录嵌套事务的嵌套级别。

internal class TransConnection
{
    public TransConnection()
    {
        this.Deeps = 0;
    }

    public DbTransaction DBTransaction { get; set; }

    public int Deeps { get; set; }
}

最后，当调用 BeginTransaction时创建TransConnection对象。之后的多个DbCommand命令都从这个事务上拿连接。因为 TransConnectionObj添加了ThreadStatic属性，所以它是线程唯一的，不会影响其它线程上的事务；所有方法执行完后，调用 CommitTransaction 就提交事务，并关闭连接；如果发生异常，则调用RollbackTransaction，就会回滚所有命令，并关闭连接。

嵌套事务示例

static void Main(string[] args)
{

    try
    {
        DBHelper.BeginTransaction();

        // add
        DBHelper.ExecuteNonQuery(CommandType.Text, "INSERT INTO TRole(ID,RoleName) VALUES('R1','MKT')");

        Transaction2();

        //detele by pk
        DBHelper.ExecuteNonQuery(CommandType.Text, "DELETE FROM TRole WHERE ID='R1'");

        Console.WriteLine(string.Format("Success and Commited"));
        DBHelper.CommitTransaction();
    }
    catch (Exception ex)
    {
        Console.WriteLine(string.Format("Exception and rollback"));
        DBHelper.RollbackTransaction();
    }

    Console.ReadLine();
}

private static void Transaction2()
{
    try
    {
        DBHelper.BeginTransaction();
        //update model
        DBHelper.ExecuteNonQuery(CommandType.Text, "UPDATE TRole SET RoleName='Marketer' WHERE ID='R1'");
        //throw new Exception("");

        DbParameter param = DBHelper.CreateInDbParameter("@ID", DbType.String, "R1");
        DbDataReader reader= DBHelper.ExecuteReader(CommandType.Text, "SELECT * FROM TRole WHERE ID=@ID",param);
        while (reader.Read())
        {
            Console.WriteLine(reader["RoleName"]);
        }

        reader.Close();

        DBHelper.CommitTransaction();
    }
    catch(Exception ex)
    {
        Console.WriteLine(string.Format("Exception and rollback: {0}", ex.Message));
        DBHelper.RollbackTransaction();
        throw;
    }
}

当为嵌套事务时，首次调用BeginTransaction，同样会创建新的TransConnection对象，深度默认为0，并保存在TransConnectionObj字段上；

第n(n>1)次调用时方法时，仅会累加嵌套的深度，不会开起新的事务。

public static void BeginTransaction()
{
    if (TransConnectionObj == null)
    {
        DbConnection conn = DBClient.GetDbConnection(ConnectionString);
        OpenConn(conn);
        DbTransaction trans = conn.BeginTransaction();
        TransConnectionObj = new TransConnection();
        TransConnectionObj.DBTransaction = trans;
    }
    else
    {
        TransConnectionObj.Deeps += 1;
    }
}

当CommitTransaction提交事务时，如果深度Deeps>0，那么表示此次提交的事务是内层事务，计数器减1即可；

当调用CommitTransaction提交事务，如果深度为0时，表示为最外层事务，刚做实际上的提交事务工作；

public static void CommitTransaction()
{
    if (TransConnectionObj == null) return;
    if (TransConnectionObj.Deeps > 0)
    {
        TransConnectionObj.Deeps -= 1;
    }
    else
    {
        TransConnectionObj.DBTransaction.Commit();
        ReleaseTransaction();
    }
}

当RollbackTransaction提交事务时，如果深度Deeps>0，那么表示此次提交的事务是内层事务，计数器减1即可;

当调用RollbackTransaction提交事务，如果深度为0时，表示为最外层事务，刚做实际上的回滚操作;

public static void RollbackTransaction()
{
    if (TransConnectionObj == null) return;
    if (TransConnectionObj.Deeps > 0)
    {
        TransConnectionObj.Deeps -= 1;
    }
    else
    {
        TransConnectionObj.DBTransaction.Rollback();
        ReleaseTransaction();
    }
}

同一个底层库，应用到不同项目时，数据库可能会不同。如果我们比较下不同数据库操作类之间的不同点，我们会发现所有的方法都是一致的，就是某些类型不同，如下表所示:

基类	SQL Server	MySql
DbConnection	SqlConnection	MySqlConnection
DbCommand	SqlCommand	MySqlCommand
DbDataAdapter	SqlDataAdapter	MySqlDataAdapte
DbParameter	SqlParameter	MySqlParameter

所以，根据子类出现的地方，可以用父类替换的原则，将SqlHeper中关于特定数据库的类，换成基类，并将创建特定数据库对象实例的代码统一到IDBClinet中

主要类有

DBHelper: 使用基类访问数据库，并聚合IDBClient来创建特定数据库对象的实例。

IDBClient: 定义创建特定数据库实例的接口，并转成基类型；

SqlServerClient：定义创建SqlServer对象的实例，并转成基类型；

MySqlCient：定义创建MySql对象的实例，并转成基类型；

DBClientFactory:根据类名动态创建IDBClient的实现类；

最后如果想要更换数据库时，只需要修改如下代码，并在配置文件中修改下连接字符串和具体的DBClient的类名：

<appSettings>
    <add key="DBConnectionString" value="Data Source=.;Initial Catalog=ProjectData;Persist Security Info=True;User ID=sa;Password=kjkj,911;"/>
    <add key="DBClient" value="SqlServerClient"/>
</appSettings>