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c#genericsdependency-injectionrepository-pattern
Blues
Blues

Reputation: 17

Repository Pattern with Generic interface and DI in EF

i have this existing code

public interface IRepository<T>
{
    void Create(T obj);
    T Retrieve(string key);
}


public class ItemRepository : IRepository<Item>
{
        public void Create(Item obj)
        {
            //codes
        }

        public Item Retrieve(string key)
        {
            //codes
        }    
}

i would like to create a General class repository where i have to inject a type of IRepository to the constructor then use its own implementation of the methods. i already have an existing code but it is currently wrong

    public class Repository
{
    IRepository<T> action = null;
    public Repository(IRepository<T> concreteImplementation)
    {
        this.action = concreteImplementation;
    }

    public void Create(T obj)
    {
        action.Create(obj);
    }
}

the classes are from EF. if there is no work around for this what will be the best approach?

Upvotes: 1

Views: 985

Answers (2)

Sam Holder
Sam Holder

Reputation: 32936

If I understand you correctly you want a single repository which can create or retrieve an object of any type by delegating to a type specific repository implementation?

How do you imagine this working? you defined this Repository class, but you have to create a concrete implementation of the actual repository in order to use it, and then still have to create an instance of Repository anyway. Why not just use the generic implementation you have to create anyway?

And what about your Retrieve method? How will this look in your Repository class? Will you just return Object? or will you make your method generic?

Anyway to answer your question, you could do this I suppose:

public class Repository
{
    IRepository action = null;
    public Repository(IRepository concreteImplementation)
    {
        this.action = concreteImplementation;
    }

    public void Create<T>(T obj)
    {
        action.Create(obj);
    }
}

but you have to introduce a non generic interface as well, as you can't require an interface with a generic parameter in the constructor without specifying the generic type on the class. 

public interface IRepository
{
    void Create(object obj);
    object Retrieve(string key);
}

Or possibly you could pass in the type into the Create method instead of having a generic parameter:

public class Repository
{
    IRepository action = null;
    public Repository(IRepository concreteImplementation, Type respositoryType)
    {
        this.action = concreteImplementation;
        expectedType=repositoryType;
    }

    public void Create(Type type, Object obj)
    {
        if(type==expected && obj.GetType()==type)
        {
            action.Create(obj);
        }
    }
}

but both of these are terrible ideas. Just use the generics and create a repository per type, it'll be best in the long run

Upvotes: 2

Kjartan
Kjartan

Reputation: 19101

I think you might just be missing the definition of T in the context of the general repository class.

Try adding <T> to the it like this:

public class Repository<T>
{
  ...
}

Upvotes: 0

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