Question

I am reletively new to Entity Framework and LINQ. I have the following code with returns a list of suppliers

    public class SupplierRepository
{
    private DataContext db = new DataContext();

    public IQueryable<Supplier> FindAllSupplier()
    {
        return db.Suppliers;
    }
}

This works fine, but I know you can use Generics with Linq and EF. so that the above code would look something like this…

    public class GenericRepository
{
    private DataContext db = new DataContext();

    public IQueryable<T> FindAll<T>()
    {
        return ...
    }
}

So that I can use it to return any type in my EF model, but I am not sure how to implement this. Can anyone advise please?

Answer 1

Instead of returning an IQueryable<T> let your repository implement IQueryable<T> and instead of wrapping a DataContext inside the repository, wrap both the DataContext and the repositories inside a unit of work. Your repository can than look like this:

public abstract class Repository<T> : IQueryable<T>
    where T : class
{
    private readonly IQueryable<T> query;

    protected Repository(IQueryable<T> query)
    {
        this.query = query;
    }

    public Type ElementType
    {
        get { return this.query.ElementType; }
    }

    public Expression Expression
    {
        get { return this.query.Expression; }
    }

    public IQueryProvider Provider
    {
        get { return this.query.Provider; }
    }

    public abstract void InsertOnSubmit(T entity);

    public abstract void DeleteOnSubmit(T entity);

    ...
}

I use this approach to effectively hide my O/RM behind an abstraction, which allows me to unit test my applicationm while still allowing to use LINQ over my repositories and have the unit of work pattern.

You can read all about it here: Faking your LINQ provider.