Question

i using below repository pattern. when i instance from the class getting this exception:

 public interface IRepository<TEntity> : IDisposable where TEntity : class
{
    IQueryable<TEntity> GetQuery();
    IEnumerable<TEntity> GetAll();
    IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate);
    TEntity Single(Expression<Func<TEntity, bool>> predicate);
    TEntity First(Expression<Func<TEntity, bool>> predicate);
    void Add(TEntity entity);
    void Delete(TEntity entity);
    void Attach(TEntity entity);
    void SaveChanges();
    void SaveChanges(SaveOptions options);
}

public class GenericRepository<TEntity> : IRepository<TEntity> where TEntity : class
{
    private ObjectContext _context;
    private IObjectSet<TEntity> _objectSet;

    public GenericRepository(ObjectContext context)
    {
        _context = context;
        _objectSet = _context.CreateObjectSet<TEntity>();
    }

    public IQueryable<TEntity> GetQuery()
    {
        return _objectSet;
    }

    public IEnumerable<TEntity> GetAll()
    {
        return GetQuery().AsEnumerable();
    }

    public IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate)
    {
        return _objectSet.Where<TEntity>(predicate);
    }

    public TEntity Single(Expression<Func<TEntity, bool>> predicate)
    {
        return _objectSet.Single<TEntity>(predicate);
    }

    public TEntity First(Expression<Func<TEntity, bool>> predicate)
    {
        return _objectSet.First<TEntity>(predicate);
    }

    public void Delete(TEntity entity)
    {
        if (entity == null)
        {
            throw new ArgumentNullException("entity");
        }

        _objectSet.DeleteObject(entity);
    }

    public void Add(TEntity entity)
    {
        if (entity == null)
        {
            throw new ArgumentNullException("entity");
        }

        _objectSet.AddObject(entity);
    }

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

    public void SaveChanges()
    {
        _context.SaveChanges();
    }

    public void SaveChanges(SaveOptions options)
    {
        _context.SaveChanges(options);
    }

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

    protected virtual void Dispose(bool disposing)
    {
        if (disposing && _context != null)
        {
            _context.Dispose();
            _context = null;
        }
    }
}

using:

 var db = new AdventureWorks2012Entities();  
 IRepository<Person> person = new GenericRepository<Person>();

exception:

Answer 1

Problem is that you are using Entity Framework 4.1 or later, which has DbContext wrapper around ObjectContext. But your repository still usess ObjectContext. Add another constructor, which accepts DbContext:

public GenericRepository(DbContext context)
{
    _context = (context as IObjectContextAdapter).ObjectContext;
    _objectSet = _context.CreateObjectSet<TEntity>();
}

You can retrieve wrapped ObjectContext instance by casting DbContext to IObjectContextAdapter interface. Another option is updating your repository class to use latest DbContext, but that will require a little bit more coding, than simply adding one constructor:

public class GenericRepository<TEntity> : IRepository<TEntity> 
   where TEntity : class
{
    private DbContext _context; // instead of ObjectContext
    private DbSet<TEntity> _set; // instead of IObjectSet<TEntity>

    public GenericRepository(DbContext context)
    {
        _context = context;
        _set = _context.Set<TEntity>();
    }

    public IQueryable<TEntity> GetQuery()
    {
        return _set;
    }

    public IEnumerable<TEntity> GetAll()
    {
        return GetQuery().AsEnumerable();
    }

    public IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate)
    {
        return _set.Where<TEntity>(predicate);
    }    

    // etc
}