Generic repository implementation with EF

Question

For a simple repository

public interface ISimpleRepository<T>
{
    IApplicationState AppState { get; set; }
    void Add(T instance);
    void Delete(T instance);
    void Delete(Guid rowGuid);
    IQueryable<T> GetAll();
    T Load(Guid rowGuid);
    void SaveChanges();
    void Update(T instance);
}

my implementation of the Load() method for specific repository for class Product might look like this:

    public Product Load(Guid rowid)
    {
        return (from c in _ctx.Products where c.id == rowid select c).FirstOrDefault();
    }

Now this is assumed when my repository implementation class looks like this:

public class EntityFrameworkProductsProvider : IRepository<Product> ...

What if I had like dozens or hundreds of this small and simple entities that would all use the same behaviour when doing CRUDs (use the same implementation of methods)? I certainly don't want to go and create a class to implement IRepository for each one of them..

I want something like this:

public class EntityFrameworkDefaultProvider<T> : IRepository<T> ...

but I don't know how to implement the LINQ Select expression then because of course I can't write from e in _ctx.T where e... or do I?

I haven't run into this scenario yet because so far I only had very specific entities with custom repository implementation.

Take a look at this article: http://bit.ly/gAoDnO. – Steven Apr 25 '11 at 14:40 — Steven, Apr 25 '11 at 14:40

score 4 · Answer 1 · edited May 23 '17 at 12:18

4

Because you tagged your question with entity-framework and entity-framework-4 I assume you are using ObjectContext API. ObjectContext offers method CreateObjectSet<T> which is equivalent of Set<T> on DbContext.

This question is actually duplicate of either:

edited May 23 '17 at 12:18

Community

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answered Apr 25 '11 at 15:11

Ladislav Mrnka

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Diego Mijelshon · Accepted Answer · 2011-04-25T23:45:58.150

3

Instead of writing _ctx.Products, you can write _ctx.Set<T>. That takes care of half of the problem (you need to add a generic constraint where T: class to your repository)

Then, if rowid is the object's key, you can use _ctx.Set<T>.Find(rowid) instead of a LINQ query to retrieve by Id.

Alternatively, you can create a base interface IHaveId (or a BaseEntity class, whatever you like) which has the Id property, and then add that as an generic constraint on T, so you can use it in your queries.

edited Apr 25 '11 at 23:45

answered Apr 25 '11 at 14:49

Diego Mijelshon

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@Diego Mijelshon: What if the id contains more then 1 column? – Naor Apr 25 '11 at 21:53
@Naor: they don't according to his interface. It's a bad practice anyway, but `Find` supports passing an `object[]` (as `params`), so he could theoretically add that too. – Diego Mijelshon Apr 25 '11 at 23:47
@Diego Mijelshon: But how the Find method knows how to map each object to each key? I asked Ladislav Mrnka also in http://stackoverflow.com/questions/5166297/generic-repository-ef4-ctp5-getbyid/5167709#5167709. – Naor Apr 26 '11 at 01:03
@Naor: By the order in which they are defined using the `HasKey` method. See http://msdn.microsoft.com/en-us/library/gg671266(v=VS.103).aspx – Diego Mijelshon Apr 26 '11 at 01:29
@Diego Mijelshon: And where does the HashKey defined? – Naor Apr 26 '11 at 01:48
@Naor: I have just sent you the link. It's all in the docs. And blog posts by the ADO.NET team. – Diego Mijelshon Apr 26 '11 at 02:11

score 2 · Answer 3 · answered Apr 25 '11 at 21:38

2

If you're using EF 4.1, see the sample generic repository here: http://www.asp.net/entity-framework/tutorials/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application

answered Apr 25 '11 at 21:38

tdykstra

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score 1 · Answer 4 · answered Apr 25 '11 at 14:52

I know that this is possible in EF4.1 with the DbContext API, where you have a "Set" method on the context that gets you the entity set corresponding to the type T. this way, you could have your repository like this:

public class EntityFrameworkDefaultProvider<T> : IRepository<T> where T:class
{
    public T Load(Guid rowId)
    {
        return _context.Set<T>().Find(rowId);
    }
}

one more remark: I think you could use this syntax :

return _ctx.Products.FirstOrDefault(c=>c.id == rowid);

to get the entity you want instead of using the (from... in...). it's clearer (in my opinion) :)

Hope this helps

Generic repository implementation with EF

4 Answers4

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