如何普遍创建从通用类型继承的存储库？ [英] How to universally create Repositories that inherit from a generic type?

问题描述

我目前正在尝试在我的DbContext之上实现存储库模式。问题是，最终我不得不将几个存储库注入到 UnitOfWork 构造函数中，如下所示：

I'm currently trying to implement the Repository Pattern on top of my DbContext. The thing is, I eventually end up with a situation where I have to inject several Repositories into a UnitOfWork constructor, like this:

public class UnitOfWork
{
    private DbContext _context;
    ICustomerRepository Customers { get; private set; }
    IEmployeeRepository Employees { get; private set; } 
    public UnitOfWork(DbContext context, ICustomerRepository cust, IEmployeeRepository emp)
    {
        _context = context;
        Customers = cust;
        Employees = emp;
    }    
}

但是，由于所有这些人都必须共享相同的DbContext，我看不到将它们作为选项注入。

However, since all of them would have to share the same DbContext, I can't see injecting them as an option.

这就是为什么我在考虑创建 RepositoryFactory 类，但是由于所有存储库都继承自通用接口，因此我发现无法创建单个 Create（）方法，因为毕竟它们没有真正的共同点

That's why I was thinking about creating a RepositoryFactory class, but since all of the repositories inherit from a generic interface I found it impossible to create a single Create() method, because, after all, they have no real common ancestor that would be a valid return type.

为了给您更多的见识，代码就是这样的：

To give you some more insight, that's how the code looks like:

public interface IRepository<TEntity> where TEntity:class
{
    TEntity Get(int id);
    IEnumerable<TEntity> GetAll();
}

---

---

public interface ICustomerRepository : IRepository<Customer>
{
    IEnumerable<Customer> GetSeniorCustomers();
}

---

---

public class CustomerRepository : ICustomerRepository
{
    private readonly DbContext _context;
    public CustomerRepository(DbContext context) : base(context)
    {
        _context = context;
    }
// ... implementation of ICustomerRepo here
}

< hr>

现在，这是当前的状态：

---

Now, that's the current state of things:

我想做的是：

public UnitOfWork(DbContext context, RepositoryFactory fac)
{
     _context = context;
     Customers = fac.Create(context, RepoType.Customer);
     Employees = fac.Create(context, RepoType.Employee);
}  

我知道它并没有给我带来更多的灵活性，但确实

I know it doesn't really give me any additional flexibility, but it does keep the code a bit less clunky in my opinion.

但是，正如我前面提到的，我无法想到Create（）方法的有效返回类型。

But, as I mentioned earlier, I cannot think of a valid return type for the Create() method.

因此，我想到了在RepositoryFactory类中创建多个方法的想法，而不是像这样的单个参数化方法：

So, I came up with the idea to create multiple methods inside the RepositoryFactory class, instead of a single parameterized one, like this:

public class RepositoryFactory
{
    public ICustomerRepository CreateCustomerRepo(DbContext context){/*...*/}
    public IEmployeeRepository CreateEmployeeRepo(DbContext context){/*...*/} 
}

所以问题是：

1. 我正在做的事情甚至可以称为工厂方法吗？


2. 如果不是，至少是一个有效的解决方案？如果没有，我如何以一种更简洁的方式实现同一件事？

1. Can the thing I'm doing be even called a Factory Method?
2. If not, is it at least a valid solution? If not, how can I achieve the same thing in a cleaner manner?

通过实现同一件事我的意思是要实现一种以可管理，简洁的方式创建这些存储库的方法。

By achieve the same thing I mean implement a way of creating those repositories in a managable, concise way.

感谢您提前获得的所有帮助。

Thank you for all the help in advance.

推荐答案

如果您不太在意打开/关闭原理，那么 RepositoryFactory类中的多个方法解决方案就很好。如果满足您的需要，则可以使用此方法。

Your "multiple methods inside the RepositoryFactory class" solution is quite good if you do not care much about Open/Close principle. If this suits your needs, you may go with this.

我正在做的事情甚至可以称为工厂方法吗？

Can the thing I'm doing be even called a Factory Method?

是；这些是工厂中的种方法。无论如何，只要它满足您的要求而又不产生新问题，就不要太在意。

Yes; those are sort of factory methods. Anyway, do not care too much as long as it fulfill your requirements without creating new problem.

如果不满足，至少是有效的解决方案？

If not, is it at least a valid solution?

如上所述，如果它满足您的需求；是的，它是有效的。

As said above, if it suits your needs; yes it is valid.

如果没有，我如何以一种更清洁的方式实现同​​一件事？

If not, how can I achieve the same thing in a cleaner manner?

另一种替代方法是工厂方法，如下所示：

Another alternative is factory method something like below:

public T CreateRepository<T>() where T : IRepositoryId
{
    IRepositoryId repository = null;
    if(typeof(T) == typeof(ICustomerRepository))
        repository = new CustomerRepository(context);
    ......
    ......
    else
        throw new XyzException("Repository type is not handled.");
    return (T)repository;
}

public interface IRepositoryId
{
    Guid RepositoryId { get; }
}

您现有的 IRepository 接口是通用的。使用该接口实现上述方法时，会产生问题。因此，只需创建其他界面即可，如上所示。从此界面派生每个存储库。

Your existing IRepository interface is generic. It creates problems while implementing above method with that interface. So, just create other interface as shown above. Derive each repository from this interface.

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