工作模式实现单元

Question

我先用ASP.NET MVC和实体框架代码创建一个应用程序。我正在使用存储库和工作模式的单元，影响来自以下链接。

http://www.asp.net/mvc/tutorials/getting-started-with-ef-5-using-mvc-4/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application

这里我对工作单元的实现有疑问，链接工作单元是通过直接在类本身中编写实体来实现的，比如。

public class UnitOfWork : IDisposable
{
    private SchoolContext context = new SchoolContext();
    private GenericRepository<Department> departmentRepository;

    public GenericRepository<Department> DepartmentRepository
    {
        get
        {

            if (this.departmentRepository == null)
            {
                this.departmentRepository = new GenericRepository<Department>(context);
            }
            return departmentRepository;
        }
    }

}

你认为这个实现足够好吗，因为每次我添加/删除实体时，我都需要改变我的工作单元类。我认为工作单元不应该依赖于实体。因为在我的应用程序中，根据客户的反馈，我们将频繁地添加/删除实体。

我可能听起来很愚蠢，但请让我知道你对此的看法。

Answer 1

实体框架中已经实现了Unit of Work模式。

DbContext是您的工作单元。每个IDbSet都是一个存储库。

using (var context = new SchoolContext())   // instantiate our Unit of Work
{
    var department = context.Departments.Find(id);
}

Answer 2

UnitOfWorkPattern有几种风格。您描述的是一个显示所有内容的方法，还有一种隐藏所有内容的方法。

public YourContext : DbContext, IContext{}

public interface IUnitOfWork{
   void Commit();
}

public UnitOfWork : IUnitOfWork{
    private readonly IContext _context;

    //IOC should always inject the same instance of this, register it accordingly
    public UnitOfWork(IContext context){
        _context = context;
    }

    void Commit(){
           // try catch the validation exception if you want to return the validations this
           // way if your confident you've already validated you can put a void here or
           // return the intfrom save changes make sure you handle the disposing properly,
           // not going into that here you also may be doing other stuff here, have multiple
           // "contexts" to save in a single transaction or we have contextProcessors that
           // do stuff based on items in the context
          _context.SaveChanges();
   }
}

这就留下了一个问题，如果您不从UnitOfWork获取存储库，那么如何将它们放入需要它们的类中。这最好由IOC框架来处理。同样，这里有几个选项。一次是将UnitOfWork注册为每个请求的单个实例，并将其注入到自定义Repository类中。

public interface IRepository<T>
{
    IQueryable<T> Records();
    //other methods go here
}

public Repository : IRepository<T>
{
    private IContext _context;

    // same instance of context injected into the unit of work, this why when you Commit
    // everything will save, this can get tricky if you start adding Add, Update and stuff
    // but EF does have the support needed.
    public Repository(IContext context)
    {
       _context = context;
    }

    public Records()
    {
        return _context.Set<T>();
    }
}

public class SomeService : ISomeService{
   private readonly _myObjectRepository;

   public SomeService(IRepository<MyObject> myObjectRepository){
       _myObjectRepository = myObjectRepository;
   }
}

就我个人而言，我认为IDbSet是一个足够的抽象，所以我不再创建存储库。但是，为了从上下文注入IDbSets，您需要将它们注册为您在IOC设置中从上下文提取的实例。这可能很复杂，根据您的技能，您可能会发现自己处于必须注册每个IDbSet的情况下，而我知道您正在努力避免。

使用IDbSet的好处是您可以访问像Add这样的简单方法，并且可以在一般意义上避免使用Entity和DbEntity的一些更复杂的部分。

public class SomeService : ISomeService {
    private readonly _myObjectSet;

    // requires specialized IOC configurations because you have to pull this instance from
    // the instance of the context, personally don't know how to do this with a single
    // registration so this has the same problem as having to add each new repository to the
    // unit of work.  In this case each new Entity I add to the context requires I add an IOC
    // registration for the type.

    public SomeService(IDbSet<MyObject> myObjectSet){
        _myObjectSet= myObjectSet;
    }
}

Answer 3

尝试将SchoolContext传递给GenericRepository：

public GenericRepository<T>
{
    private SchoolContext _context;

    public GenericRepository(SchoolContext context)
    {
       _context = context;
    }

    public Get(int id)
    {
        return _context.Set<T>().Find(id);
    }
}

并使用：

using(var context = new SchoolContext())
{
    var departmentRepository = new GenericRepository<Department>(context);
    var department = departmentRepository.Get(1);
}