Entity Framework and Unit of Work

Question

I am using EF/Repository/Unit of Work, but I am having a hard time understanding some details. Inside the UnitOfWork, I create a new EF DbContext (EmmaContext), but look at inside the repository, I cast it which I know is wrong, how do I get the context inside the repo correctly? Maybe I am totally on the wrong path?

Here is my UnitOfWork:

//Interface
public interface IUnitOfWork : IDisposable
{
    void Commit();
}

//Implementation
public class UnitOfWork : IUnitOfWork
{
    #region Fields/Properties
    private bool isDisposed = false;
    public EmmaContext Context { get; set; }
    #endregion

    #region Constructor(s)
    public UnitOfWork()
    {
        this.Context = new EmmaContext();
    }
    #endregion

    #region Methods
    public void Commit()
    {
        this.Context.SaveChanges();
    }

    public void Dispose()
    {
        if (!isDisposed)
            Dispose(true);
        GC.SuppressFinalize(this);
    }

    private void Dispose(bool disposing)
    {
        isDisposed = true;
        if (disposing)
        {
            if (this.Context != null)
                this.Context.Dispose();
        }
    }
    #endregion
}

Here is the repository:

//Interface
public interface IRepository<TEntity> where TEntity : class
{
    IQueryable<TEntity> Query();
    void Add(TEntity entity);
    void Attach(TEntity entity);
    void Delete(TEntity entity);
    void Save(TEntity entity);
}

//Implementation
public abstract class RepositoryBase<TEntity> : IRepository<TEntity> where TEntity : class
{
    #region Fields/Properties
    protected EmmaContext context;
    protected DbSet<TEntity> dbSet;
    #endregion

    #region Constructor(s)
    public RepositoryBase(IUnitOfWork unitOfWork)
    {
        this.context = ((UnitOfWork)unitOfWork).Context;
        this.dbSet = context.Set<TEntity>();
    }
    #endregion

    #region Methods
    public void Add(TEntity entity)
    {
        dbSet.Add(entity);
    }

    public void Attach(TEntity entity)
    {
        dbSet.Attach(entity);
    }

    public void Delete(TEntity entity)
    {
        dbSet.Remove(entity);
    }

    public IQueryable<TEntity> Query()
    {
        return dbSet.AsQueryable();
    }

    public void Save(TEntity entity)
    {
        Attach(entity);
        context.MarkModified(entity);
    }
    #endregion
}

Answer 1

Sam: I usually feel comfortable with a concrete Repository taking a concrete UnitOfWork in the ctor:

   public RepositoryBase(UnitOfWork unitOfWork)
   {
        this.context = unitOfWork.Context;
        this.dbSet = context.Set<TEntity>();
   }

The repository and UoW typically work in concert and need to know a little bit about each other.

Of course the code consuming these classes only know about the interface definitions and not the concrete types.

Answer 2

This is the best article I've read.

In their example, they manage the repositories like this:

    private SchoolContext context = new SchoolContext();
    private GenericRepository<Department> departmentRepository;
    private GenericRepository<Course> courseRepository;

    public GenericRepository<Department> DepartmentRepository
    {
        get
        {

            if (this.departmentRepository == null)
            {
                this.departmentRepository = new GenericRepository<Department>(context);
            }
            return departmentRepository;
        }
    }

Your unit of work holds the context, and if it needs to reference a repository, it creates it if it has not been created, and passes in the context that it's holding.

The article also walks through how they converted a regular MVC controller implementation into using the unit of work pattern.