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Thinking In Design Pattern——Unit Of Work(工作单元)模式探索

什么是Unit Of Work模式

Unit Of Work(工作单元)模式用来维护一个由已经被业务事物修改(增加、删除或更新)的业务对象组成的列表。Unit  Of Work模式负责协调这些修改的持久化工作以及所有标记的并发问题。在数据访问层中采用Unit Of Work模式带来的好处是能够确保数据完整性。如果在持久化一系列业务对象(他们属于同一个事物)的过程中出现问题,那么应该将所有的修改回滚,以确保数据始终处于有效状态。

为了演示Unit Of Work模式,使用一个简单的银行领域对两个账号之间的转账建模。下图给出了服务层(AccountService)与使用了Unit Of Work模式(以确保转账作为原子事物的Unit Of Work提交)的资源层(AccountRepository)之间的交互。

 

记住这张图,因为下面的代码逻辑都是依照这张图的定义来实现的。

建立Infrastructure

  • 下面开始编写解决方案的代码,首先创建Unit Of Work模式的所有配套的基础设施代码
 public interface IAggregateRoot
    {
    }

IAggregateRoot接口实际上属于标记接口,这个接口充当了类和方法的元数据,我们构建的资源库只持久化实现了IAggregateRoot接口的业务对象,所以Unit Of Work的实现将使用IAggregateRoot接口来引用原子事物中涉及的任何业务实体

  • 添加另外一个接口IUnitOfWorkRepository,这是一个用来持久化操作的接口:
 public interface IUnitOfWorkRepository
    {
        void PersistCreationOf(IAggregateRoot entity);
        void PersistUpdateOf(IAggregateRoot entity);
        void PersistDeletionOf(IAggregateRoot entity);
    }
  • 之后,向Infrastructure项目中添加IUnitOfWork接口:
 public interface IUnitOfWork
    {
        void RegisterAmended(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository);
        void RegisterNew(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository);
        void RegisterRemoved(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository);
        void Commit();
    }

 值得注意的是IUnitOfWork接口在注册修改/增加/删除时需要IUnitOfWorkRepository,这样在提交时,Unit Of Work可以将真正持久化的工作委托给适当的具体实现。

  • 最后向Infrastructure项目中添加UnitOfWork,实现IUnitOfWork:
 public class UnitOfWork : IUnitOfWork 
    {
        private Dictionary<IAggregateRoot, IUnitOfWorkRepository> addedEntities;
        private Dictionary<IAggregateRoot, IUnitOfWorkRepository> changedEntities;
        private Dictionary<IAggregateRoot, IUnitOfWorkRepository> deletedEntities;

        public UnitOfWork()
        {
            addedEntities = new Dictionary<IAggregateRoot, IUnitOfWorkRepository>();
            changedEntities = new Dictionary<IAggregateRoot, IUnitOfWorkRepository>();
            deletedEntities = new Dictionary<IAggregateRoot, IUnitOfWorkRepository>();
        }

        public void RegisterAmended(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository)
        {
            if (!changedEntities.ContainsKey(entity))
            {
                changedEntities.Add(entity, unitofWorkRepository);
            }
        }

        public void RegisterNew(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository)
        {
            if (!addedEntities.ContainsKey(entity))
            {
                addedEntities.Add(entity, unitofWorkRepository);
            };
        }

        public void RegisterRemoved(IAggregateRoot entity, IUnitOfWorkRepository unitofWorkRepository)
        {
            if (!deletedEntities.ContainsKey(entity))
            {
                deletedEntities.Add(entity, unitofWorkRepository);
            }
        }
        
        public void Commit()
        {
            using (TransactionScope scope = new TransactionScope())
            {
                foreach (IAggregateRoot entity in this.addedEntities.Keys)
                {
                    this.addedEntities[entity].PersistCreationOf(entity);
                }

                foreach (IAggregateRoot entity in this.changedEntities.Keys)
                {
                    this.changedEntities[entity].PersistUpdateOf(entity);
                }

                foreach (IAggregateRoot entity in this.deletedEntities.Keys)
                {
                    this.deletedEntities[entity].PersistDeletionOf(entity);
                }

                scope.Complete(); 
            }
        }

    }

UnitOfWork类使用3个字典变量来跟踪对业务实体的代执行修改。第一个字典对应于被添加到数据存储的实体,第2个字典跟踪带更新的实体,而第三个字典处理实体删除,与字典中的实体键匹配的IUnitOfWorkRepository将被保存下来,并用于Commit方法之中,来调用Repository对象,该对象包含真正持久化实体的代码。Commit方法遍历每一个字典,并调用相应的IUnitOfWorkRepository方法(传递实体引用)。Commit方法中的工作均被TransactionScope代码包装起来,如果在IUnitOfWorkRepository中执行任务时出现异常,则所有工作回滚,数据存储将保持原来的状态。

建立Model

  • 向Model中添加一个新类Account,表示银行账户,为了方便演示简单处理了:
public class Account : IAggregateRoot 
    {
        public decimal balance { get; set; }
    }
  •   为了将Accout持久化,添加IAccountRepository接口:
public interface IAccountRepository
    {
        void Save(Account account);
        void Add(Account account);
        void Remove(Account account);                
    }
  • 添加AccountService服务类来协调两个账户之间的转账工作。
public class AccountService
    {
        private IAccountRepository _accountRepository;
        private IUnitOfWork _unitOfWork;
        /// <summary>
        /// AccountService通过其构造器实现依赖注入
        /// </summary>
        /// <param name="accountRepository"></param>
        /// <param name="unitOfWork"></param>
        public AccountService(IAccountRepository accountRepository,
                              IUnitOfWork unitOfWork)
        {
            _accountRepository = accountRepository;
            _unitOfWork = unitOfWork;            
        }
        /// <summary>
        /// 实现两个账户之间转账工作
        /// </summary>
        /// <param name="from"></param>
        /// <param name="to"></param>
        /// <param name="amount"></param>
        public void Transfer(Account from, Account to, decimal amount)
        {
            if (from.balance >= amount)
            {
                from.balance -= amount;
                to.balance += amount;

                _accountRepository.Save(from);
                _accountRepository.Save(to);
                _unitOfWork.Commit();
            }
        }
    }

接着,它调用账户Repository来保存两个账户,最后,它调用Unit Of Work实例的Commit方法来确保该交易作为原子的Unit Of Work完成。所以接下来的重点就是怎样Repository与Unit Of Work交互。

建立Repository来持久化业务实体

 public class AccountRepository : IAccountRepository, IUnitOfWorkRepository 
    {
        private IUnitOfWork _unitOfWork;

        public AccountRepository(IUnitOfWork unitOfWork)
        {
            _unitOfWork = unitOfWork;
        }

        public void Save(Account account)
        {            
            _unitOfWork.RegisterAmended(account, this);            
        }

        public void Add(Account account)
        {
            _unitOfWork.RegisterNew(account, this);
        }

        public void Remove(Account account)
        {
            _unitOfWork.RegisterRemoved(account, this);
        }  

        public void PersistUpdateOf(IAggregateRoot entity)
        {
            // ADO.net or EF、NH来持久化
        }

        public void PersistCreationOf(IAggregateRoot entity)
        {
            // ADO.net or EF、NH来持久化
        }

        public void PersistDeletionOf(IAggregateRoot entity)
        {
            // ADO.net or EF、NH来持久化
        }              
    }

OK,这样Unit Of Work工作模式就搭建好了,AccountRepository实现了IAccountRepositoryIUnitOfWorkRepository接口,IAccountRepository方法的实现简单地将工作委托给Unit Of Work(传入待持久化的实体以及Repository的引用),最后,调用Unit Of Work类的Commit方法,其实是Unit Of Work引用Repository的IUnitOfWorkRepository的接口契约来真正完成持久化任务,至于持久化操作你可以用Ado.net或者EF、NH等。

回过头来再看这幅图,原来Unit Of Work也就是如此罢了:

posted @ 2012-10-29 23:57 木宛城主 阅读(...) 评论(...) 编辑 收藏
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