Compiled Linq with Generic Repository Design Pattern

I've been looking开发者_JS百科 around the web but I've yet to found any information on this. As we know Linq gives us CompiledQuery which transform the expression into T-SQL before running it. I'm trying to design a generic repository to interact with my EF but with the exception the Linq queries is compiled. If anyone could shead some light on this that would be great :)

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It is hardly possible because if you want to pre-compile query you must know it. With generic repository you usually have only this:

public interface IRepository<T>
{
  IQueryable<T> GetQuery();
}

So the code using a repository instance is responsible for defining the query. Pre-compilation requires concrete repository which will contain methods like:

IEnumerable<Order> GetOrdersWithHeaderAndItemsByDate(DateTime date, int take, int skip);
IEnumerable<OrderHeader> GetOrderHeadersOrderedByCustomer(int take, int skip);

etc.

Obviously you can hardly prepare such queries in generic repository beacuse they are dependent on concrete entity.

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You are looking for an implementation of the Specification pattern. Basically, this is creating a Specification object that contains the information needed to filter your query. By using Specifications, you can have a Generic Repository implementation, and put your custom query logic in the specification. The specification base class looks something like:

public class Specification<TEntity>
{
   public Specification(Expression<Func<TEntity, bool>> predicate)
   {
       _predicate = predicate;
   }

   public bool IsSatisfiedBy(TEntity entity)
   {
       return _predicate.Compile().Invoke(entity);
   }

   public Expression<Func<TEntity,bool>> PredicateExpression{
       get{ return _predicate; }
   }      

   private Expression<Func<TEntity, bool>> _predicate;
} 

A very helpful article about implementing the specification pattern with the Entity Framework can be found at http://huyrua.wordpress.com/2010/07/13/entity-framework-4-poco-repository-and-specification-pattern/