Added possibility to chain includes. (#331)

* Added possibility to chain includes.

* Removed interface.

* Removed the need for generating GUIDs as ids and added tests.

src/ApplicationCore/Helpers/Query/IncludeAggregator.cs

@@ -0,0 +1,26 @@
+using Microsoft.eShopWeb.ApplicationCore.Interfaces;
+using System;
+using System.Collections.Generic;
+using System.Linq.Expressions;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Helpers.Query
+{
+    public class IncludeAggregator<TEntity>
+    {
+        public IncludeQuery<TEntity, TProperty> Include<TProperty>(Expression<Func<TEntity, TProperty>> selector)
+        {
+            var visitor = new IncludeVisitor();
+            visitor.Visit(selector);
+
+            var pathMap = new Dictionary<IIncludeQuery, string>();
+            var query = new IncludeQuery<TEntity, TProperty>(pathMap);
+
+            if (!string.IsNullOrEmpty(visitor.Path))
+            {
+                pathMap[query] = visitor.Path;
+            }
+
+            return query;
+        }
+    }
+}

src/ApplicationCore/Helpers/Query/IncludeQuery.cs

@@ -0,0 +1,19 @@
+using Microsoft.eShopWeb.ApplicationCore.Interfaces;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Helpers.Query
+{
+    public class IncludeQuery<TEntity, TPreviousProperty> : IIncludeQuery<TEntity, TPreviousProperty>
+    {
+        public Dictionary<IIncludeQuery, string> PathMap { get; } = new Dictionary<IIncludeQuery, string>();
+        public IncludeVisitor Visitor { get; } = new IncludeVisitor();
+
+        public IncludeQuery(Dictionary<IIncludeQuery, string> pathMap)
+        {
+            PathMap = pathMap;
+        }
+
+        public HashSet<string> Paths => PathMap.Select(x => x.Value).ToHashSet();
+    }
+}

src/ApplicationCore/Helpers/Query/IncludeQueryExtensions.cs

@@ -0,0 +1,66 @@
+using Microsoft.eShopWeb.ApplicationCore.Interfaces;
+using System;
+using System.Collections.Generic;
+using System.Linq.Expressions;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Helpers.Query
+{
+    public static class IncludeQueryExtensions
+    {
+        public static IIncludeQuery<TEntity, TNewProperty> Include<TEntity, TPreviousProperty, TNewProperty>(
+            this IIncludeQuery<TEntity, TPreviousProperty> query,
+            Expression<Func<TEntity, TNewProperty>> selector)
+        {
+            query.Visitor.Visit(selector);
+
+            var includeQuery = new IncludeQuery<TEntity, TNewProperty>(query.PathMap);
+            query.PathMap[includeQuery] = query.Visitor.Path;
+
+            return includeQuery;
+        }
+
+        public static IIncludeQuery<TEntity, TNewProperty> ThenInclude<TEntity, TPreviousProperty, TNewProperty>(
+            this IIncludeQuery<TEntity, TPreviousProperty> query,
+            Expression<Func<TPreviousProperty, TNewProperty>> selector)
+        {
+            query.Visitor.Visit(selector);
+
+            // If the visitor did not generated a path, return a new IncludeQuery with an unmodified PathMap.
+            if (string.IsNullOrEmpty(query.Visitor.Path))
+            {
+                return new IncludeQuery<TEntity, TNewProperty>(query.PathMap);
+            }
+
+            var pathMap = query.PathMap;
+            var existingPath = pathMap[query];
+            pathMap.Remove(query);
+
+            var includeQuery = new IncludeQuery<TEntity, TNewProperty>(query.PathMap);
+            pathMap[includeQuery] = $"{existingPath}.{query.Visitor.Path}";
+
+            return includeQuery;
+        }
+
+        public static IIncludeQuery<TEntity, TNewProperty> ThenInclude<TEntity, TPreviousProperty, TNewProperty>(
+            this IIncludeQuery<TEntity, IEnumerable<TPreviousProperty>> query,
+            Expression<Func<TPreviousProperty, TNewProperty>> selector)
+        {
+            query.Visitor.Visit(selector);
+
+            // If the visitor did not generated a path, return a new IncludeQuery with an unmodified PathMap.
+            if (string.IsNullOrEmpty(query.Visitor.Path))
+            {
+                return new IncludeQuery<TEntity, TNewProperty>(query.PathMap);
+            }
+
+            var pathMap = query.PathMap;
+            var existingPath = pathMap[query];
+            pathMap.Remove(query);
+
+            var includeQuery = new IncludeQuery<TEntity, TNewProperty>(query.PathMap);
+            pathMap[includeQuery] = $"{existingPath}.{query.Visitor.Path}";
+
+            return includeQuery;
+        }
+    }
+}

src/ApplicationCore/Helpers/Query/IncludeVisitor.cs

@@ -0,0 +1,16 @@
+using System.Linq.Expressions;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Helpers.Query
+{
+    public class IncludeVisitor : ExpressionVisitor
+    {
+        public string Path { get; private set; } = string.Empty;
+
+        protected override Expression VisitMember(MemberExpression node)
+        {
+            Path = string.IsNullOrEmpty(Path) ? node.Member.Name : $"{node.Member.Name}.{Path}";
+
+            return base.VisitMember(node);
+        }
+    }
+}

src/ApplicationCore/Interfaces/IIncludeQuery.cs

@@ -0,0 +1,16 @@
+using Microsoft.eShopWeb.ApplicationCore.Helpers.Query;
+using System.Collections.Generic;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Interfaces
+{
+    public interface IIncludeQuery
+    {
+        Dictionary<IIncludeQuery, string> PathMap { get; }
+        IncludeVisitor Visitor { get; }
+        HashSet<string> Paths { get; }
+    }
+
+    public interface IIncludeQuery<TEntity, out TPreviousProperty> : IIncludeQuery
+    {
+    }
+}

src/ApplicationCore/Specifications/BaseSpecification.cs

@@ -2,6 +2,7 @@
 using System;
 using System.Linq.Expressions;
 using System.Collections.Generic;
+using Microsoft.eShopWeb.ApplicationCore.Helpers.Query;
 
 namespace Microsoft.eShopWeb.ApplicationCore.Specifications
 {
@@ -26,6 +27,13 @@ namespace Microsoft.eShopWeb.ApplicationCore.Specifications
         {
             Includes.Add(includeExpression);
         }
+
+        protected virtual void AddIncludes<TProperty>(Func<IncludeAggregator<T>, IIncludeQuery<T, TProperty>> includeGenerator)
+        {
+            var includeQuery = includeGenerator(new IncludeAggregator<T>());
+            IncludeStrings.AddRange(includeQuery.Paths);
+        }
+
         protected virtual void AddInclude(string includeString)
         {
             IncludeStrings.Add(includeString);

src/ApplicationCore/Specifications/CustomerOrdersWithItemsSpecification.cs

@@ -1,4 +1,5 @@
 using Microsoft.eShopWeb.ApplicationCore.Entities.OrderAggregate;
+using Microsoft.eShopWeb.ApplicationCore.Helpers.Query;
 
 namespace Microsoft.eShopWeb.ApplicationCore.Specifications
 {
@@ -7,8 +8,7 @@ namespace Microsoft.eShopWeb.ApplicationCore.Specifications
         public CustomerOrdersWithItemsSpecification(string buyerId)
             : base(o => o.BuyerId == buyerId)
         {
-            AddInclude(o => o.OrderItems);
-            AddInclude($"{nameof(Order.OrderItems)}.{nameof(OrderItem.ItemOrdered)}");
+            AddIncludes(query => query.Include(o => o.OrderItems).ThenInclude(i => i.ItemOrdered));
         }
     }
 }