Paging infrastructure implemented through specifications. (#151)

* Paging criterias added in BaseSpecification. New paginated specification added (CatalogFilterPaginatedSpecification) . EFRepository cleaned up and paging implementation added. Usage of the new paging infrastructure in CatalogService (Web and WebRazor).

* Use IReadOnlyList<T> instead of List<T> as return type from repositories.

* - Ordering possibility added in the specification.
- Evaluation of the specification placed in separate class.

src/ApplicationCore/Interfaces/IAsyncRepository.cs

@@ -7,10 +7,11 @@ namespace Microsoft.eShopWeb.ApplicationCore.Interfaces
     public interface IAsyncRepository<T> where T : BaseEntity
     {
         Task<T> GetByIdAsync(int id);
-        Task<List<T>> ListAllAsync();
-        Task<List<T>> ListAsync(ISpecification<T> spec);
+        Task<IReadOnlyList<T>> ListAllAsync();
+        Task<IReadOnlyList<T>> ListAsync(ISpecification<T> spec);
         Task<T> AddAsync(T entity);
         Task UpdateAsync(T entity);
         Task DeleteAsync(T entity);
+        Task<int> CountAsync(ISpecification<T> spec);
     }
 }

src/ApplicationCore/Interfaces/IRepository.cs

@@ -12,5 +12,6 @@ namespace Microsoft.eShopWeb.ApplicationCore.Interfaces
         T Add(T entity);
         void Update(T entity);
         void Delete(T entity);
+        int Count(ISpecification<T> spec);
     }
 }

src/ApplicationCore/Interfaces/ISpecification.cs

@@ -9,5 +9,11 @@ namespace Microsoft.eShopWeb.ApplicationCore.Interfaces
         Expression<Func<T, bool>> Criteria { get; }
         List<Expression<Func<T, object>>> Includes { get; }
         List<string> IncludeStrings { get; }
+        Expression<Func<T, object>> OrderBy { get; }
+        Expression<Func<T, object>> OrderByDescending { get; }
+
+        int Take { get; }
+        int Skip { get; }
+        bool isPagingEnabled { get;}
     }
 }