generic repository EF4 CTP5 getById

问题

I have a generic repository an I am trying to add a GetById method as shown here C# LINQ to SQL: Refactoring this Generic GetByID method

The problem is my repository does not use System.Data.Linq.DataContext instead I use System.Data.Entity.DbContext

So I get errors where I try to use

Mapping.GetMetaType

and

return _set.Where( whereExpression).Single();

How can I implement a generic GetById method in CTP5? Should I be using System.Data.Entity.DbContext in my Repository.

Here is the start of my repository class

  public class BaseRepository<T> where T : class
    {

        private DbContext _context;
        private readonly DbSet<T> _set;

        public BaseRepository()
        {
            _context = new MyDBContext();
            _set = _context.Set<T>();

        }

回答1:

The most basic approach is simply

public T GetById(params object[] keys)
{
  _set.Find(keys);
}

If you know that all your entities have primary key called Id (it doesn't have to be called Id in DB but it must be mapped to property Id) of defined type you can use simply this:

public interface IEntity
{
  int Id { get; }
}

public class BaseRepository<T> where T : class, IEntity
{
  ...

  public T GetById(int id)
  {
    _set.Find(id);
  }
}

If data type is not always the same you can use:

public interface IEntity<TKey>
{
  TKey Id { get; }
}

public class BaseRepository<TEntity, TKey> where TEntity : class, IEntity<TKey>
{
  ...

  public TEntity GetById(TKey id)
  {
    _set.Find(id);
  }
}

You can also simply use:

public class BaseRepository<TEntity, TKey> where TEntity : class
{
  ...

  public TEntity GetById(TKey id)
  {
    _set.Find(id);
  }
}

回答2:

try this

    public virtual T GetByID(object id)
    {

        // Define the entity key values.
        IEnumerable<KeyValuePair<string, object>> entityKeyValues =
            new KeyValuePair<string, object>[] { 
            new KeyValuePair<string, object>("Id", id) };

        string qualifiedEntitySetName = _context.DefaultContainerName + "." + typeof(T).Name;
        EntityKey key = new EntityKey(qualifiedEntitySetName, entityKeyValues);

        return (T)_context.GetObjectByKey(key);           
    }

来源：https://stackoverflow.com/questions/5166297/generic-repository-ef4-ctp5-getbyid