Using repository model in n-tiered application - entity-framework

Question

This is a subject that I have given some thought to and just tried to get a POC working but I am getting a bit lost to be honest.
So I have a 3 tiered web app, the traditional DAL, BAL & FE structure for the purpose of this exercise.
The DAL has reference to my DB through Entity Framework and from this we gain access to a single table JobInfo.
The BAL references the DAL project and has this interface:
public interface IJobInfoRepository
{
IEnumerable<JobInfo> SelectAll();
JobInfo SelectByID(string id);
void Insert(JobInfo obj);
void Update(JobInfo obj);
void Delete(string id);
void Save();
}
Then I have this class:
public class JobInfoRepository : IJobInfoRepository
{
public JobInfoRepository()
{
_db = new TestEntities();
}
public JobInfoRepository(TestEntities db)
{
_db = db;
}
private TestEntities _db = null;
public IEnumerable<JobInfo> SelectAll()
{
return _db.JobInfoes.ToList();
}
public JobInfo SelectByID(string id)
{
return _db.JobInfoes.Find(id);
}
public void Insert(JobInfo obj)
{
_db.JobInfoes.Add(obj);
}
public void Update(JobInfo obj)
{
_db.Entry(obj).State = EntityState.Modified;
}
public void Delete(string id)
{
JobInfo existing = _db.JobInfoes.Find(id);
_db.JobInfoes.Remove(existing);
}
public void Save()
{
_db.SaveChanges();
}
}
In my FE project I reference the BAL project. But this is where I'm lost. Without giving FE access to the DAL project and therefore having visibility to my JobInfo entity how can the FE code perform any of the CRUD operations in the BAL project?
Thanks,
Dave

Answer 1

You can use two different approaches.
You can create a project that only holds the entity definition (POCO classes) and reference it from all the projects
You can do asyou did in 1. but use models and map them to the entities using AutoMapper or ValueInjecter
The advantage of 2 is that you really decopule the models used in the BL and FE from the entities used by your persisntence layer (DAL). You could also apply this disctintion between the model of the BL and the models that you'll show or edit in the FE (for example implementing view models in MVC).
If you're implementing a simple project, perhaps you'll be satisfied with 1. But if you're implementing something a bit more complicated it can be advisable to use 2.
By the way, instead of implementing a Repository for each entity you'll spare a lot of time if you implemente a base generic repository (i.e Repository<T>) and inherit it for each entity, to implemente only the extar functionality which is not available in the base repository.
Using EF it's easy to implement a generic repository because you can use the DbSet<T> collections.