实体框架：使用通用存储库从多个实体检索数据

Question

I have created a Web API Project in which I am implementing a repository pattern. In a nutshell, I have the following structure.

Controller
    |
Business/Service Layer
    |
Repository
    |
DB-Access

Here is a code of one of my Service Layer:

public class DashboardService : IDashboardService
{   
    private readonly IRepository<USERROLE> repoUserRole;
    private readonly IRepository<ROLEEXT> repoRoleExt;  

    public void GetUserInstitution(string UserId)
    {
        repoUserRole.GetList(x => x.ID == UserId, null).Join(
            repoRoleExt.GetList(),
            uRole => uRole.ROLEID, roleEx => roleEx.ROLEID, (uRole, roleEx) => new
            {
                USERROLE = uRole,
                ROLEEXT = roleEx
            }).ToList();
    }
}

GetList Method in Repository looks like this:

public class Repository<T> : IRepository<T> where T : class, new()
{
    // Some code omitted
    public IEnumerable<T> GetList()
    {
        return DbSet.ToList();
    }

    public IEnumerable<T> GetList(Expression<Func<T, bool>> predicate, params string[] navigationProperties)
    {
        IEnumerable<T> list;
        var query = DbSet.AsQueryable();
        if (navigationProperties != null && navigationProperties.Length > 0)
        {
            foreach (string navigationProperty in navigationProperties)
            {
                query = query.Include(navigationProperty);
            }
        }
        list = query.Where(predicate).ToList<T>();
        return list;
    }
}

What I want:

• A Generic method which can take multiple entities(join them) and return the resultset. (Also where should that method be? (Business or Repo)

As seen in my code I have followed the following approach:

• Create Instance of Each Repository <=> Entity type object
• Using those objects retrieve data

Problem:

• Not sure if this is a correct approach of implementing the repository pattern!
• If not What would be the best way to handle this?

PS: I am aware of error present in the GetUserInstitution method.

Edit : Also, If not using Generic repository, do I have to create multiple repository based on Entites?

Answer 1

You should really consider just creating separate repositories with separate different contracts for each entity and not resort to trying to create a generic repository. Not all of your repositories will NEED to return a list, and it doesnt make sense to have repositories that dont implement methods to have boilerplate NotImplementedExceptions or things like that. Instead, follow the approach taken my many engineers of just creating separate contracts/interfaces for each repository. It may appear that creating a single generic repository would be following the SRP rule, but after you begin creating more and more repositories, youll begin to see some idiosyncratic attributes of the repositories, and in the end your just better of without generic repository.

One case for creating an interface for a repository class is as follows

public interface IRepository<T> where T : IAggregateRoot

Then, you would use it as

    public interface IOrderRepository : IRepository<Order>
{
Order Add(Order order);
// ...
}

IAggregateRoot above is the marker interface pattern.

Honestly, I would just start out with different contracts per repository, and later if it makes sense to add the IRepository, do so.