EF的Code First开始模式时，在设计Data层与Data First模式稍微有些不同，它主要有数据库类,数据库操作基类，数据通用操作接口和数据通过操作实现组成，每个类有自己的用途，先看一下最简单的结构：

DataContext是ＥＦ的数据库对象类型，它里面的代码构架了我们的数据表对象

 public class DataContext : DbContext, IDataContext
    {
        #region Properties

        /// <summary>
        /// 得ì?到ì?UserBase结¨￠果?集?￥
        /// </summary>
        public IDbSet<UserBase> UserBases { get; private set; }
        /// <summary>
        /// 得ì?到ì?UserInfo结¨￠果?集?￥
        /// </summary>
        public IDbSet<UserInfo> UserInfos { get; private set; }
        /// <summary>
        /// 得ì?到ì?Category结¨￠果?集?￥
        /// </summary>
        public IDbSet<Category> Categorys { get; private set; }
        #endregion

        #region Constructors
        public DataContext()
            : base(DataContext.GetConnectionString())
        {
            InitDbSets();

        }

        public DataContext(string cs)
            : base(cs)
        {
            InitDbSets();
        }

        #endregion

        #region  Private Methods
        private void InitDbSets()
        {
            UserBases = this.Set<UserBase>();
            UserInfos = this.Set<UserInfo>();
            Categorys = this.Set<Category>();
            Init();//数oy据Y库a与??DBContext依°¨¤附?方¤?式o?　?
        }

        /// <summary>
        /// 得ì?到ì?数oy据Y连￠?接¨?串??
        /// </summary>
        /// <returns></returns>
        private static string GetConnectionString()
        {
            string conn;
            if (System.Diagnostics.Debugger.IsAttached)
            {
                conn = VConfigs.WebInfoConfig.Get_Config().DevsSqlConn;
            }
            else
            {
                conn = VConfigs.WebInfoConfig.Get_Config().ReleaseSqlConn;
            }
            return conn;
        }
        /// <summary>
        /// 根¨′据Y传??入¨?的ì?类¤¨¤型¨a，ê?进?行DDBContext出?始o?化?￥
        /// </summary>
        /// <param name="InitType"></param>
        private static void SetInitializer(InitializerTypes InitType)
        {
            switch (InitType)
            {
                case InitializerTypes.Standard:
                    Database.SetInitializer(new CreateDatabaseIfNotExists<DataContext>());
                    break;
                case InitializerTypes.ReCreateAlways:
                    Database.SetInitializer(new DropCreateDatabaseAlways<DataContext>());
                    break;
                case InitializerTypes.ReCreateByChange:
                    Database.SetInitializer(new DropCreateDatabaseIfModelChanges<DataContext>());
                    break;
                default:
                    break;
            }
        }
        /// <summary>
        /// DBContext初?始o?化?￥方¤?法¤?§
        /// </summary>
        private static void Init()
        {
            Database.DefaultConnectionFactory = new SqlConnectionFactory();
            if (System.Diagnostics.Debugger.IsAttached)
            {
                DataContext.SetInitializer(InitializerTypes.ReCreateByChange);
            }
            else
            {
                DataContext.SetInitializer(InitializerTypes.Standard);
            }
        }
        #endregion

        /// <summary>
        /// 数oy据Y库a建?§立￠?é时o?à执??行D
        /// </summary>
        /// <param name="modelBuilder"></param>
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
 
        }

    }

其中dataBase就是数据库操作基类，主要实现创建dbcontext对象和对修改进行统一提交的作用

/// <summary>
    /// 数oy据Y库a基¨′类¤¨¤
    /// </summary>
    public abstract class DataBase
    {

        #region 单ì￡¤件t模?ê式o?创???建?§一°?个?类¤¨¤对?象¨?

        /// <summary>
        /// 数oy据Y源??对?象¨?
        /// </summary>
        private static DataContext _db = null;
        protected static DataContext CreateInstance()
        {
            if (_db == null)
                _db = new DataContext();
            return _db;
        }
        #endregion

        /// <summary>
        /// 数oy据Y库a访¤?问¨o对?象¨?
        /// </summary>
        protected DataContext Db = CreateInstance();
        /// <summary>
        /// 统a3一°?提?¨￠交?动?￥作á??
        /// </summary>
        protected virtual void SubmitChanges()
        {
            try
            {
                Db.SaveChanges();
            }
            catch (Exception ex)
            {
                throw;
            }
        }
    }

而数据操作统一接口主要实现对数据库的ＣＵＲＤ操作，代码一般是这样（与其它构架大同小异）

 /// <summary>
    /// 通a?§用??数oy据Y库a访¤?问¨o接¨?口¨2
    /// </summary>
    public interface IRepository<TEntity> where TEntity : Entity.BaseEntity
    {
        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤更¨1新?记?录?
        /// </summary>
        /// <param name="entity"></param>
        void Update(TEntity entity);

 
        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤[批¨2量￠?]更¨1新?记?录?
        /// </summary>
        /// <param name="entity"></param>
        void Update(IList<TEntity> list);

       
        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤插?入¨?记?录?
        /// </summary>
        void Insert(TEntity entity);

        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤[批¨2量￠?]插?入¨?记?录?
        /// </summary>
        void Insert(IList<TEntity> list);

        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤插?入¨?记?录?并?é返¤|ì回?刚?刚?立￠?é即??插?入¨?的ì?状á??态??视o¨?图a?
        /// </summary>
        TEntity InsertGetIDENTITY(TEntity entity);

        /// <summary>
        /// 根¨′据Y数oy据Y库a实o|ì体??-a》?¤多¨¤主??键¨1,删|?除y有?D多¨¤个?参?数oy控?制?的ì?对?象¨?
        /// </summary>
        /// <param name="oArr"></param>
        void Delete(TEntity entity);

        /// <summary>
        /// 返¤|ì回?默?认¨?结¨￠果?集?￥
        /// </summary>
        /// <returns></returns>
        IQueryable<TEntity> GetModel();

        /// <summary>
        /// 根¨′据Y主??键¨1返¤|ì回?实o|ì体??
        /// </summary>
        /// <returns></returns>
        TEntity GetModelById(int id);

    }

事实上我们真实的datacontext对象在实现开发中只有Data本层可见，而对于业务层和ＵＩ层是不被容许访问的，当然这也是保存原数据对象及方便扩展和维护的一种作法。

本文转自博客园张占岭（仓储大叔）的博客，原文链接：EF架构~Code First构架~Data层的实现，如需转载请自行联系原博主。