Using the repository pattern with Entity Framework (mvc storefront)

Question

Hi,

can anyone give a helping hand, I been watching the videos for the mvc storefront and have create my own website using these techniques i.e. DDD, Repository pattern but i wish to use Entity Framework.

In the Interfaces it returns IQueryable but with the entity framework i should return ObjectQuery instead? - I will be using LINQ.

Also in the storedfront example it goes something like this IQueryable GetCategories(); (couldn't enter greater than and less than punctuation here as stackoverflow seems to strip them)

As in the mvc stored the Category class was a build entity class (standard class) but with the entity framework these classes are prebuilt in the object context - are they not?

So i should need to build them.

I am a little confused, if anyone has any helpful example or code it would be really helpful.

As i say i have watched the videos from THe mvc storefront using linq2sql but really would like to use the entity framework.

Any ideas?

Thanks

Smithy

Answer 1

Maybe if you see the Contact Manager Tutorial in the http://www.asp.net/learn/mvc/#MVC_SampleApp site, they use the Repository Pattern and the Entity Framework.

Answer 2

Let me answer your questions one at a time:

Your repositories should return IQueryable<T>, not ObjectQuery. The reason is that the whole purpose of the repository pattern is to abstract away the specifics of your data store. This allows you to do things like substitute a mock repository when you unit test your controllers. If you make the repository return ObjectQuery, then you are not abstracting away the Entity Framework. Another way of saying this is the users of your repository should not know, as much as possible, but it is the Entity Framework which is doing the O/R mapping.

In order to use the greater than and less than symbols in paragraph text in Stack Overflow, you must escape them as you would in HTML, i.e.:

<

You do not need to do this in a code block; in code blocks, you just type the less than/greater than symbol.

Answer 3

thanks both for your comments! Its really been helpful and the contact manager is going to be really helpful

Answer 4

Im not sure if thats correct, but i`m using L2E, translating generated objects to domain objects using AutoMapper 3rd party tool.

Answer 5

I started like you a few weeks ago, you will see it's pretty easy to work with EF. My project is small so i'm using the entities generated by the EF as my model classes, and you can add your own logic to them using a partial class.

Here's a simple method of one of my repositories, as a example:

    /// <summary>
    /// Finds a user by it's credentials
    /// </summary>
    /// <param name="oUser"></param>
    /// <returns></returns>
    public User FindByCredentials(string username, Byte[] password)
    {
        User user = null;

        if (!Validators.IsStringEmptyOrNull(username))
        {
            user = this.FindByCredentialsQuery(username, password).FirstOrDefault<User>();
        }

        return (Validators.IsNull(user)) ? new User() : user;

    }


    /// <summary>
    /// Finds a user by it's credentials
    /// </summary>
    /// <param name="username"></param>
    /// <param name="password"></param>
    /// <returns></returns>
    protected IQueryable<User> FindByCredentialsQuery(string username, Byte[] password)
    {
        var query = from Users in this.UserDataContext.Users
                    where
                        (Users.Username == username) &&
                        (Users.Password == password) &&
                        (Users.Enabled == true)
                    select Users;


        return query;
    }

Note that i'm using IQueryable only inside the repository, and return only the list of entities requested. This way i can control that the query to DB is always executed inside the Repo.