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;}
     }
 }

src/ApplicationCore/Specifications/BaseSpecification.cs

@@ -14,6 +14,12 @@ namespace Microsoft.eShopWeb.ApplicationCore.Specifications
         public Expression<Func<T, bool>> Criteria { get; }
         public List<Expression<Func<T, object>>> Includes { get; } = new List<Expression<Func<T, object>>>();
         public List<string> IncludeStrings { get; } = new List<string>();
+        public Expression<Func<T, object>> OrderBy { get; private set; }
+        public Expression<Func<T, object>> OrderByDescending { get; private set; }
+
+        public int Take { get; private set; }
+        public int Skip { get; private set; }
+        public bool isPagingEnabled { get; private set; } = false;
 
         protected virtual void AddInclude(Expression<Func<T, object>> includeExpression)
         {
@@ -23,5 +29,19 @@ namespace Microsoft.eShopWeb.ApplicationCore.Specifications
         {
             IncludeStrings.Add(includeString);
         }
+        protected virtual void ApplyPaging(int skip, int take)
+        {
+            Skip = skip;
+            Take = take;
+            isPagingEnabled = true;
+        }
+        protected virtual void ApplyOrderBy(Expression<Func<T, object>> orderByExpression)
+        {
+            OrderBy = orderByExpression;
+        }
+        protected virtual void ApplyOrderByDescending(Expression<Func<T, object>> orderByDescendingExpression)
+        {
+            OrderByDescending = orderByDescendingExpression;
+        }
     }
 }

src/ApplicationCore/Specifications/CatalogFilterPaginatedSpecification.cs

@@ -0,0 +1,14 @@
+using Microsoft.eShopWeb.ApplicationCore.Entities;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Specifications
+{
+    public class CatalogFilterPaginatedSpecification : BaseSpecification<CatalogItem>
+    {
+        public CatalogFilterPaginatedSpecification(int skip, int take, int? brandId, int? typeId)
+            : base(i => (!brandId.HasValue || i.CatalogBrandId == brandId) &&
+                (!typeId.HasValue || i.CatalogTypeId == typeId))
+        {
+            ApplyPaging(skip, take);
+        }
+    }
+}

src/Infrastructure/Data/EfRepository.cs

@@ -20,6 +20,10 @@ namespace Microsoft.eShopWeb.Infrastructure.Data
         {
             _dbContext = dbContext;
         }
+        private IQueryable<T> ApplySpecification(ISpecification<T> spec)
+        {
+            return SpecificationEvaluator<T>.GetQuery(_dbContext.Set<T>().AsQueryable(), spec);
+        }
 
         public virtual T GetById(int id)
         {
@@ -42,44 +46,26 @@ namespace Microsoft.eShopWeb.Infrastructure.Data
             return _dbContext.Set<T>().AsEnumerable();
         }
 
-        public async Task<List<T>> ListAllAsync()
+        public async Task<IReadOnlyList<T>> ListAllAsync()
         {
             return await _dbContext.Set<T>().ToListAsync();
         }
 
         public IEnumerable<T> List(ISpecification<T> spec)
         {
-            // fetch a Queryable that includes all expression-based includes
-            var queryableResultWithIncludes = spec.Includes
-                .Aggregate(_dbContext.Set<T>().AsQueryable(),
-                    (current, include) => current.Include(include));
-
-            // modify the IQueryable to include any string-based include statements
-            var secondaryResult = spec.IncludeStrings
-                .Aggregate(queryableResultWithIncludes,
-                    (current, include) => current.Include(include));
-
-            // return the result of the query using the specification's criteria expression
-            return secondaryResult
-                            .Where(spec.Criteria)
-                            .AsEnumerable();
+            return ApplySpecification(spec).AsEnumerable();
         }
-        public async Task<List<T>> ListAsync(ISpecification<T> spec)
+        public async Task<IReadOnlyList<T>> ListAsync(ISpecification<T> spec)
         {
-            // fetch a Queryable that includes all expression-based includes
-            var queryableResultWithIncludes = spec.Includes
-                .Aggregate(_dbContext.Set<T>().AsQueryable(),
-                    (current, include) => current.Include(include));
-
-            // modify the IQueryable to include any string-based include statements
-            var secondaryResult = spec.IncludeStrings
-                .Aggregate(queryableResultWithIncludes,
-                    (current, include) => current.Include(include));
-
-            // return the result of the query using the specification's criteria expression
-            return await secondaryResult
-                            .Where(spec.Criteria)
-                            .ToListAsync();
+            return await ApplySpecification(spec).ToListAsync();
+        }
+        public int Count(ISpecification<T> spec)
+        {
+            return ApplySpecification(spec).Count();
+        }
+        public async Task<int> CountAsync(ISpecification<T> spec)
+        {
+            return await ApplySpecification(spec).CountAsync();
         }
 
         public T Add(T entity)

src/Infrastructure/Data/SpecificationEvaluator.cs

@@ -0,0 +1,44 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.eShopWeb.ApplicationCore.Entities;
+using Microsoft.eShopWeb.ApplicationCore.Interfaces;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Microsoft.eShopWeb.Infrastructure.Data
+{
+    public class SpecificationEvaluator<T> where T : BaseEntity
+    {
+        public static IQueryable<T> GetQuery(IQueryable<T> inputQuery, ISpecification<T> specification)
+        {
+            var query = inputQuery;
+
+            // modify the IQueryable using the specification's criteria expression
+            if (specification.Criteria != null)
+                query = query.Where(specification.Criteria);
+
+            // Includes all expression-based includes
+            query = specification.Includes.Aggregate(query,
+                                    (current, include) => current.Include(include));
+
+            // Include any string-based include statements
+            query = specification.IncludeStrings.Aggregate(query,
+                                    (current, include) => current.Include(include));
+
+            // Apply ordering if expressions are set
+            if (specification.OrderBy != null)
+                query = query.OrderBy(specification.OrderBy);
+            else if (specification.OrderByDescending != null)
+                query = query.OrderByDescending(specification.OrderByDescending);
+
+            // Apply paging if enabled
+            if (specification.isPagingEnabled)
+            {
+                query = query.Skip(specification.Skip)
+                             .Take(specification.Take);
+            }
+            return query;
+        }
+    }
+}

src/Web/Services/CatalogService.cs

@@ -42,14 +42,12 @@ namespace Microsoft.eShopWeb.Web.Services
             _logger.LogInformation("GetCatalogItems called.");
 
             var filterSpecification = new CatalogFilterSpecification(brandId, typeId);
-            var root = _itemRepository.List(filterSpecification);
+            var filterPaginatedSpecification =
+                new CatalogFilterPaginatedSpecification(itemsPage * pageIndex, itemsPage, brandId, typeId);
 
-            var totalItems = root.Count();
-
-            var itemsOnPage = root
-                .Skip(itemsPage * pageIndex)
-                .Take(itemsPage)
-                .ToList();
+            // the implementation below using ForEach and Count. We need a List.
+            var itemsOnPage = _itemRepository.List(filterPaginatedSpecification).ToList();
+            var totalItems = _itemRepository.Count(filterSpecification);
 
             itemsOnPage.ForEach(x =>
             {

src/WebRazorPages/Services/CatalogService.cs

@@ -43,14 +43,12 @@ namespace Microsoft.eShopWeb.RazorPages.Services
             _logger.LogInformation("GetCatalogItems called.");
 
             var filterSpecification = new CatalogFilterSpecification(brandId, typeId);
-            var root = _itemRepository.List(filterSpecification);
+            var filterPaginatedSpecification =
+                new CatalogFilterPaginatedSpecification(itemsPage * pageIndex, itemsPage, brandId, typeId);
 
-            var totalItems = root.Count();
-
-            var itemsOnPage = root
-                .Skip(itemsPage * pageIndex)
-                .Take(itemsPage)
-                .ToList();
+            // the implementation below using ForEach and Count. We need a List.
+            var itemsOnPage = _itemRepository.List(filterPaginatedSpecification).ToList();
+            var totalItems = _itemRepository.Count(filterSpecification);
 
             itemsOnPage.ForEach(x =>
             {