仓储模式Repository的选择与设计

首次接触仓储的概念来自Eric Evans 的经典著作《领域驱动设计－软件核心复杂性应对之道》，但书中没有具体实现。如何实现仓储模式，在我这几年的使用过程中也积累了一些具体的实施经验。根据项目的大小、可维护性、可扩展性，以及并发我们可以做以下几种设计；

1、项目小，扩展性差

public interface IRepository<T> where T : class,new()
    {
        /// <summary>
        /// 创建对象
        /// </summary>
        /// <param name="model"></param>
        /// <returns></returns>
        T Create(T model);

        /// <summary>
        /// 更新对象
        /// </summary>
        /// <param name="model"></param>
        /// <returns></returns>
        T Update(T model);

        /// <summary>
        /// 根据对象全局唯一标识检索对象
        /// </summary>
        /// <param name="guid"></param>
        /// <returns></returns>
        T Retrieve(Guid guid);

        /// <summary>
        /// 根据条件表达式检索对象
        /// </summary>
        /// <param name="expression">条件表达式</param>
        /// <returns></returns>
        /// <exception cref = "ArgumentNullException" > source 为 null</exception>
        T Retrieve(Expression<Func<T, bool>> expression);

        /// <summary>
        /// 根据对象全局唯一标识删除对象
        /// </summary>
        /// <param name="guid">对象全局唯一标识</param>
        /// <returns>删除的对象数量</returns>
        int Delete(Guid guid);

        /// <summary>
        /// 根据对象全局唯一标识集合删除对象集合
        /// </summary>
        /// <param name="guids">全局唯一标识集合</param>
        /// <returns>删除的对象数量</returns>
        int BatchDelete(IList<Guid> guids);

        List<T> GetAll();

        List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total);
    }

IRepository接口包含了CRUD操作，如果在业务中还需要扩展，只需在IRepository接口中添加即可。

public class RepositoryImpl<T> : IRepository<T> where T : class, new()
    {
        protected readonly string ConnectionString;

        protected RepositoryImpl(ISqlHelp sqlHelp)
        {
            ConnectionString = sqlHelp.SQLConnectionString();
        }

        public int BatchDelete(IList<Guid> guids)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                foreach (var item in guids)
                {
                    var model = dbcontext.Set<T>().Find(item);
                    dbcontext.Entry(model).State = EntityState.Deleted;
                }
                return dbcontext.SaveChanges();
            }
        }

        public T Create(T model)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                dbcontext.Entry(model).State = EntityState.Added;
                var createRowCount = dbcontext.SaveChanges();
                return createRowCount >  ? model : null;
            }
        }

        /// <summary>
        /// 删除模型
        /// </summary>
        /// <param name="guid">指定的全局标识</param>
        /// <returns>删除数量</returns>
        /// <exception cref="ArgumentOutOfRangeException"></exception>
        public int Delete(Guid guid)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                var model = dbcontext.Set<T>().Find(guid);
                if (model == null) throw new ArgumentOutOfRangeException(nameof(guid));
                dbcontext.Entry(model).State = EntityState.Deleted;
                return dbcontext.SaveChanges();
            }
        }

        public List<T> GetAll()
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().Where(q => true).ToList();
            }
        }

        public List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                total = dbcontext.Set<T>().Where(expression).Count();
                switch (sortOrder)
                {
                    case SortOrder.Ascending:
                        return dbcontext.Set<T>().Where(expression).OrderBy(sortPredicate).Skip(skip).Take(take).ToList();

                    case SortOrder.Descending:
                        return dbcontext.Set<T>().Where(expression).OrderByDescending(sortPredicate).Skip(skip).Take(take).ToList();

                }
                throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
            }
        }

        /// <summary>
        /// 返回序列中的第一个元素
        /// </summary>
        /// <param name="expression">查询表达式</param>
        /// <returns>T</returns>
        /// <exception cref="ArgumentNullException">source 为 null</exception>
        public T Retrieve(Expression<Func<T, bool>> expression)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().FirstOrDefault(expression);
            }
        }

        public T Retrieve(Guid guid)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().Find(guid);
            }
        }

        public T Update(T model)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                dbcontext.Entry(model).State = EntityState.Modified;
                var updateRowAcount = dbcontext.SaveChanges();
                return updateRowAcount >  ? model : null;
            }
        }
    }

RepositoryImpl为IRepository接口的实现。其中ISqlHelp接口包含获取数据库链接字符串的功能，DbContext为EntityFramework类库。

public sealed class UserServer
    {
        private readonly IRepository<User> _userRepository;

        public UserServer(IRepository<User> userRepository)
        {
            _userRepository = userRepository;
        }

        public void CreateUser()
        {
            var user = new User();
            _userRepository.Create(user);
        }
    }

这是最简单的仓储使用方式，优点是简单、快速，缺点是扩展性差且违反开放-关闭原则（Open-Close Principle）。但如果项目小且项目生存周期短可选择此模式进行快速搭建。

---

2、项目大，可扩展性好，不对并发做处理。

因为项目要求高扩展性，每次修改都对IRepository修改也违反软件设计原则。这里IRepository接口不变，但是RepositoryImpl做如下修改：

public class RepositoryImpl<T> : IRepository<T> where T : class, new()
    {
        protected readonly string ConnectionString;

        protected RepositoryImpl(ISqlHelp sqlHelp)
        {
            ConnectionString = sqlHelp.SQLConnectionString();
        }

        public virtual int BatchDelete(IList<Guid> guids)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                foreach (var item in guids)
                {
                    var model = dbcontext.Set<T>().Find(item);
                    dbcontext.Entry(model).State = EntityState.Deleted;
                }
                return dbcontext.SaveChanges();
            }
        }

        public virtual T Create(T model)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                dbcontext.Entry(model).State = EntityState.Added;
                var createRowCount = dbcontext.SaveChanges();
                return createRowCount >  ? model : null;
            }
        }

        /// <summary>
        /// 删除模型
        /// </summary>
        /// <param name="guid">指定的全局标识</param>
        /// <returns>删除数量</returns>
        /// <exception cref="ArgumentOutOfRangeException"></exception>
        public virtual int Delete(Guid guid)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                var model = dbcontext.Set<T>().Find(guid);
                if (model == null) throw new ArgumentOutOfRangeException(nameof(guid));
                dbcontext.Entry(model).State = EntityState.Deleted;
                return dbcontext.SaveChanges();
            }
        }

        public virtual List<T> GetAll()
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().Where(q => true).ToList();
            }
        }

        public virtual List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                total = dbcontext.Set<T>().Where(expression).Count();
                switch (sortOrder)
                {
                    case SortOrder.Ascending:
                        return dbcontext.Set<T>().Where(expression).OrderBy(sortPredicate).Skip(skip).Take(take).ToList();

                    case SortOrder.Descending:
                        return dbcontext.Set<T>().Where(expression).OrderByDescending(sortPredicate).Skip(skip).Take(take).ToList();

                }
                throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
            }
        }

        /// <summary>
        /// 返回序列中的第一个元素
        /// </summary>
        /// <param name="expression">查询表达式</param>
        /// <returns>T</returns>
        /// <exception cref="ArgumentNullException">source 为 null</exception>
        public virtual T Retrieve(Expression<Func<T, bool>> expression)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().FirstOrDefault(expression);
            }
        }

        public virtual T Retrieve(Guid guid)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                return dbcontext.Set<T>().Find(guid);
            }
        }

        public virtual T Update(T model)
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                dbcontext.Entry(model).State = EntityState.Modified;
                var updateRowAcount = dbcontext.SaveChanges();
                return updateRowAcount >  ? model : null;
            }
        }
    }
}

即在每个方法实现上加上了virtual关键字使方法可以重载。在示例1中业务使用User对象的仓储方式为IRepository<User>，如果业务需要针对User对象集合做批量修改，这时就必须去修改IRepository和RepositoryImpl，所以这里将添加接口IUserRepository，

    /// <summary>
    /// 用户仓储接口
    /// </summary>
    public interface IUserRepository:IRepository<User>
    {
        /// <summary>
        /// 批量修改用户生日
        /// </summary>
        void BatchUpdateUserBirthday();
    }

UserRepositoryImpl实现为

public sealed class UserRepositoryImpl: RepositoryImpl<User>,IUserRepository
    {
        public UserRepositoryImpl(ISqlHelp sqlHelp) : base(sqlHelp)
        {

        }

        public void BatchUpdateUserBirthday()
        {
            using (var dbcontext = new DbContext(ConnectionString))
            {
                var usersFromDb = dbcontext.Set<User>().Where(q => q.Name.Equals("zhang"));
                foreach (var item in usersFromDb)
                {
                    item.Name = "wang";
                    dbcontext.Entry(item).State = EntityState.Modified;
                }
                dbcontext.SaveChanges();
            }
        }
    }

这里不对代码的实现合理性做讨论，只是为了说明仓储模式的设计。

而在业务层中的使用如下：

public sealed class UserServer
    {
        private readonly IUserRepository _userRepository;

        public UserServer(IUserRepository userRepository)
        {
            _userRepository = userRepository;
        }

        public void CreateUser()
        {
            var user = new User();
            _userRepository.Create(user);
        }

        public void BatchUpdateBirthDay()
        {
            _userRepository.BatchUpdateUserBirthday();
        }

此仓储模式在实际使用中稍显复杂，每添加一个实体，需要添加对应的接口和实现两个文件，但是这里的一点复杂度换来代码的高扩展性和维护性是值得的。

3、项目庞大，扩展性高，有并发处理需求

因为项目涉及高并发，采用仓储模式+工作单元模式的设计，使用工作单元的原因是可以提高数据库写操作负载，并且在仓储模式中可以根据不同的数据库链接字符串读不同的库。

对于并发的，可以分为多线程、并行处理、异步编程、响应式编程。（引用：《Concurrency in C# Cookbook》—Author，Stephen Cleary）

在仓储中我会使用异步编程实现并发。

仓储接口如下：

public interface IRepository<T> where T:class,IEntity,new ()
    {
        /// <summary>
        /// 根据条件表达式获取集合
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        Task<List<T>> FindByAsync(Expression<Func<T, bool>> predicate);

        IQueryable<T> FindQueryableByAsync(Expression<Func<T, bool>> predicate);

        /// <summary>
        /// 根据对象全局唯一标识检索对象
        /// </summary>
        /// <param name="ID"></param>
        /// <returns></returns>
        Task<T> RetrieveAsync(Guid ID);

        /// <summary>
        /// 根据条件表达式检索对象
        /// </summary>
        /// <param name="predicate"></param>
        /// <returns></returns>
        Task<T> RetrieveAsync(Expression<Func<T, bool>> predicate);

        /// <summary>
        /// 获取所有数据
        /// </summary>
        /// <returns></returns>
        Task<List<T>> GetAllAsync();

        /// <summary>
        /// 获取所有数据
        /// </summary>
        /// <returns></returns>
        List<T> GetAll();

        /// <summary>
        /// 根据条件表示分页获取数据集合
        /// </summary>
        /// <param name="predicate">断言表达式</param>
        /// <param name="sortPredicate">排序断言</param>
        /// <param name="sortOrder">排序方式</param>
        /// <param name="skip">跳过序列中指定数量的元素，然后返回剩余的元素</param>
        /// <param name="take">从序列的开头返回指定数量的连续元素</param>
        /// <returns>item1：数据集合；item2：数据总数</returns>
        Task<Tuple<List<T>,int>> GetAllAsync(Expression<Func<T, bool>> predicate, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take);
    }

工作单元接口如下：

/// <summary>
    /// Unit Of Work Pattern
    /// </summary>
    public interface IUnitOfWork : IDisposable
    {
        DbContext DbContext { get; set; }

        /// <summary>
        /// 提交所有更改
        /// </summary>
        Task CommitAsync();

        #region Methods
        /// <summary>
        /// 将指定的聚合根标注为“新建”状态。
        /// </summary>
        /// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
        /// <param name="obj">需要标注状态的聚合根。</param>
        void RegisterNew<T>(T obj)
            where T : class, IEntity;
        /// <summary>
        /// 将指定的聚合根标注为“更改”状态。
        /// </summary>
        /// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
        /// <param name="obj">需要标注状态的聚合根。</param>
        void RegisterModified<T>(T obj)
            where T : class;
        /// <summary>
        /// 将指定的聚合根标注为“删除”状态。
        /// </summary>
        /// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
        /// <param name="obj">需要标注状态的聚合根。</param>
        void RegisterDeleted<T>(T obj)
            where T : class;
        #endregion
    }

仓储实现如下：

public class RepositoryImpl<T> : IRepository<T> where T : class, IEntity, new()
    {
        protected readonly DbContext Context;

        protected RepositoryImpl(IContextHelper contextHelper)
        {
            Context = contextHelper.DbContext;
        }

        public virtual async Task<List<T>> FindByAsync(Expression<Func<T, bool>> predicate)
        {
            return await Context.Set<T>().Where(predicate).ToListAsync();
        }

        public virtual IQueryable<T> FindQueryableByAsync(Expression<Func<T, bool>> predicate)
        {
            return Context.Set<T>().Where(predicate);
        }

        public virtual async Task<List<T>> GetAllAsync()
        {
            return await Context.Set<T>().ToListAsync();
        }

        public List<T> GetAll()
        {
            return Context.Set<T>().ToList();
        }

        public virtual async Task<Tuple<List<T>, int>> GetAllAsync(Expression<Func<T, bool>> predicate,
            Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take)
        {
            var result = Context.Set<T>().Where(predicate);
            var total = result.Count();
            switch (sortOrder)
            {

                case SortOrder.Ascending:
                    var resultAscPaged = await
                        Context.Set<T>().Where(predicate).OrderBy(sortPredicate).Skip(skip).Take(take).ToListAsync();
                    return new Tuple<List<T>, int>(resultAscPaged, total);

                case SortOrder.Descending:
                    var resultDescPaged = await
                        Context.Set<T>().Where(predicate)
                            .OrderByDescending(sortPredicate)
                            .Skip(skip)
                            .Take(take).ToListAsync();
                    return new Tuple<List<T>, int>(resultDescPaged, total);
            }
            throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
        }

        public virtual async Task<T> RetrieveAsync(Expression<Func<T, bool>> predicate)
        {
            return await Context.Set<T>().FirstOrDefaultAsync(predicate);
        }

        public virtual async Task<T> RetrieveAsync(Guid id)
        {
            return await Context.Set<T>().FindAsync(id);
        }
    }

工作单元实现如下：

public class UnitOfWork : IUnitOfWork
    {
        public DbContext DbContext { get; set; }
        public UnitOfWork(IContextHelper contextHelp)
        {
            DbContext = contextHelp.DbContext;
        }

        /// <summary>
        /// Saves all pending changes
        /// </summary>
        /// <returns>The number of objects in an Added, Modified, or Deleted state</returns>
        public virtual async Task CommitAsync()
        {
            // Save changes with the default options
            try
            {
                await DbContext.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException ex)
            {
                ex.Entries.Single().Reload();
            }

        }

        /// <summary>
        /// Disposes the current object
        /// </summary>
        public virtual void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Disposes all external resources.
        /// </summary>
        /// <param name="disposing">The dispose indicator.</param>
        private void Dispose(bool disposing)
        {
            if (!disposing) return;
            if (DbContext == null) return;

            DbContext.Dispose();
            DbContext = null;
        }

        public virtual void RegisterNew<TEntity>(TEntity obj) where TEntity : class, IEntity
        {
            DbContext.Set<TEntity>().Add(obj);
        }

        public virtual void RegisterModified<TEntity>(TEntity obj) where TEntity : class
        {
            DbContext.Entry(obj).State = EntityState.Modified;
        }

        public virtual void RegisterDeleted<TEntity>(TEntity obj) where TEntity : class
        {
            DbContext.Entry(obj).State = EntityState.Deleted;
        }

    }

在业务层中的使用同2。