add test for querying HasManyThrough

Author: jaredcnance

Diff for: src/Examples/JsonApiDotNetCoreExample/Controllers/ArticlesController.cs

@@ -0,0 +1,15 @@
+using JsonApiDotNetCore.Controllers;
+using JsonApiDotNetCore.Services;
+using JsonApiDotNetCoreExample.Models;
+
+namespace JsonApiDotNetCoreExample.Controllers
+{
+    public class ArticlesController : JsonApiController<Article>
+    {
+        public ArticlesController(
+            IJsonApiContext jsonApiContext,
+            IResourceService<Article> resourceService) 
+            : base(jsonApiContext, resourceService)
+        { }
+    }
+}

Diff for: src/Examples/JsonApiDotNetCoreExample/Data/AppDbContext.cs

@@ -31,13 +31,15 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
             modelBuilder.Entity<CourseStudentEntity>()
                 .HasOne(r => r.Course)
                 .WithMany(c => c.Students)
-                .HasForeignKey(r => r.CourseId)
-                ;
+                .HasForeignKey(r => r.CourseId);
 
             modelBuilder.Entity<CourseStudentEntity>()
                 .HasOne(r => r.Student)
                 .WithMany(s => s.Courses)
                 .HasForeignKey(r => r.StudentId);
+
+            modelBuilder.Entity<ArticleTag>()
+                .HasKey(bc => new { bc.ArticleId, bc.TagId });
         }
 
         public DbSet<TodoItem> TodoItems { get; set; }

Diff for: src/Examples/JsonApiDotNetCoreExample/Models/ArticleTag.cs

@@ -1,8 +1,6 @@
-using JsonApiDotNetCore.Models;
-
 namespace JsonApiDotNetCoreExample.Models
 {
-    public class ArticleTag : Identifiable
+    public class ArticleTag
     {
         public int ArticleId { get; set; }
         public Article Article { get; set; }

Diff for: src/JsonApiDotNetCore/Builders/ContextGraphBuilder.cs

@@ -173,15 +173,20 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
                         throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}'. Type does not contain a property named '{hasManyThroughAttribute.InternalThroughName}'.");
 
                     // assumption: the property should be a generic collection, e.g. List<ArticleTag>
-                    if(prop.PropertyType.IsGenericType == false)
+                    if(throughProperty.PropertyType.IsGenericType == false)
                         throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}'. Expected through entity to be a generic type, such as List<{prop.PropertyType}>.");
-                    hasManyThroughAttribute.ThroughType = prop.PropertyType.GetGenericArguments()[0];
+
+                    hasManyThroughAttribute.ThroughType = throughProperty.PropertyType.GetGenericArguments()[0];
 
                     var throughProperties = hasManyThroughAttribute.ThroughType.GetProperties();
+                    
                     // Article → ArticleTag.Article
-                    hasManyThroughAttribute.LeftProperty = throughProperties.Single(x => x.PropertyType == entityType);
+                    hasManyThroughAttribute.LeftProperty = throughProperties.SingleOrDefault(x => x.PropertyType == entityType)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a navigation property to type {entityType}");
+                  
                     // Article → ArticleTag.Tag
-                    hasManyThroughAttribute.RightProperty = throughProperties.Single(x => x.PropertyType == hasManyThroughAttribute.Type);
+                    hasManyThroughAttribute.RightProperty = throughProperties.SingleOrDefault(x => x.PropertyType == hasManyThroughAttribute.Type)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a navigation property to type {hasManyThroughAttribute.Type}");
                 }
             }
 

Diff for: src/JsonApiDotNetCore/Builders/DocumentBuilder.cs

@@ -177,8 +177,9 @@ private RelationshipData GetRelationshipData(RelationshipAttribute attr, Context
                     relationshipData.Links.Related = linkBuilder.GetRelatedRelationLink(contextEntity.EntityName, entity.StringId, attr.PublicRelationshipName);
             }
 
-            // this only includes the navigation property, we need to actually check the navigation property Id
-            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationship(entity, attr.InternalRelationshipName);
+             // this only includes the navigation property, we need to actually check the navigation property Id
+            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationshipValue(entity, attr);
+
             if (navigationEntity == null)
                 relationshipData.SingleData = attr.IsHasOne
                     ? GetIndependentRelationshipIdentifier((HasOneAttribute)attr, entity)
@@ -213,7 +214,7 @@ private List<ResourceObject> IncludeRelationshipChain(
         {
             var requestedRelationship = relationshipChain[relationshipChainIndex];
             var relationship = parentEntity.Relationships.FirstOrDefault(r => r.PublicRelationshipName == requestedRelationship);
-            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationship(parentResource, relationship.InternalRelationshipName);
+            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationship(parentResource, relationship.InternalRelationshipName);    
             if (navigationEntity is IEnumerable hasManyNavigationEntity)
             {
                 foreach (IIdentifiable includedEntity in hasManyNavigationEntity)
@@ -226,7 +227,7 @@ private List<ResourceObject> IncludeRelationshipChain(
             {
                 included = AddIncludedEntity(included, (IIdentifiable)navigationEntity);
                 included = IncludeSingleResourceRelationships(included, (IIdentifiable)navigationEntity, relationship, relationshipChain, relationshipChainIndex);
-            }
+            }        
 
             return included;
         }
@@ -284,16 +285,14 @@ private ResourceObject GetIncludedEntity(IIdentifiable entity)
 
         private List<ResourceIdentifierObject> GetRelationships(IEnumerable<object> entities)
         {
-            var objType = entities.GetElementType();
-
-            var typeName = _jsonApiContext.ContextGraph.GetContextEntity(objType);
-
+            string typeName = null;
             var relationships = new List<ResourceIdentifierObject>();
             foreach (var entity in entities)
             {
+                typeName = _jsonApiContext.ContextGraph.GetContextEntity(entity.GetType()).EntityName;
                 relationships.Add(new ResourceIdentifierObject
                 {
-                    Type = typeName.EntityName,
+                    Type = typeName,
                     Id = ((IIdentifiable)entity).StringId
                 });
             }

Diff for: src/JsonApiDotNetCore/Data/DefaultEntityRepository.cs

@@ -275,8 +275,8 @@ public virtual IQueryable<TEntity> Include(IQueryable<TEntity> entities, string
                 }
 
                 internalRelationshipPath = (internalRelationshipPath == null)
-                    ? relationship.InternalRelationshipName
-                    : $"{internalRelationshipPath}.{relationship.InternalRelationshipName}";
+                    ? relationship.RelationshipPath
+                    : $"{internalRelationshipPath}.{relationship.RelationshipPath}";
 
                 if(i < relationshipChain.Length)
                     entity = _jsonApiContext.ContextGraph.GetContextEntity(relationship.Type);

Diff for: src/JsonApiDotNetCore/Internal/ContextGraph.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
+using JsonApiDotNetCore.Models;
 
 namespace JsonApiDotNetCore.Internal
 {
@@ -19,6 +21,19 @@ public interface IContextGraph
         /// </example>
         object GetRelationship<TParent>(TParent resource, string propertyName);
 
+        /// <summary>
+        /// Gets the value of the navigation property, defined by the relationshipName,
+        /// on the provided instance.
+        /// </summary>
+        /// <param name="resource">The resource instance</param>
+        /// <param name="relationship">The attribute used to define the relationship.</param>
+        /// <example>
+        /// <code>
+        /// _graph.GetRelationshipValue(todoItem, nameof(TodoItem.Owner));
+        /// </code>
+        /// </example>
+        object GetRelationshipValue<TParent>(TParent resource, RelationshipAttribute relationship) where TParent : IIdentifiable;
+
         /// <summary>
         /// Get the internal navigation property name for the specified public
         /// relationship name.
@@ -107,6 +122,29 @@ public object GetRelationship<TParent>(TParent entity, string relationshipName)
             return navigationProperty.GetValue(entity);
         }
 
+        public object GetRelationshipValue<TParent>(TParent resource, RelationshipAttribute relationship) where TParent : IIdentifiable
+        {
+            if(relationship is HasManyThroughAttribute hasManyThroughRelationship) 
+            {
+                return GetHasManyThrough(resource, hasManyThroughRelationship);
+            }
+
+            return GetRelationship(resource, relationship.InternalRelationshipName);
+        }
+
+        private IEnumerable<IIdentifiable> GetHasManyThrough(IIdentifiable parent, HasManyThroughAttribute hasManyThrough)
+        {
+            var throughProperty = GetRelationship(parent, hasManyThrough.InternalThroughName);
+            if (throughProperty is IEnumerable hasManyNavigationEntity)
+            {
+                foreach (var includedEntity in hasManyNavigationEntity)
+                {
+                    var targetValue = hasManyThrough.RightProperty.GetValue(includedEntity) as IIdentifiable;
+                    yield return targetValue;
+                }
+            }
+        }
+
         /// </ inheritdoc>
         public string GetRelationshipName<TParent>(string relationshipName)
         {
@@ -125,5 +163,5 @@ public string GetPublicAttributeName<TParent>(string internalAttributeName)
                 .SingleOrDefault(a => a.InternalAttributeName == internalAttributeName)?
                 .PublicAttributeName;
         }
-  }
+    }
 }

Diff for: src/JsonApiDotNetCore/Models/HasManyThroughAttribute.cs

@@ -80,5 +80,11 @@ public HasManyThroughAttribute(string publicName, string internalThroughName, Li
         ///
         /// </example>
         public PropertyInfo RightProperty { get; internal set; }
+
+        /// <inheritdoc />
+        /// <example>
+        /// "ArticleTags.Tag"
+        /// </example>
+        public override string RelationshipPath => $"{InternalThroughName}.{RightProperty.Name}";
     }
 }

Diff for: src/JsonApiDotNetCore/Models/RelationshipAttribute.cs

@@ -25,7 +25,7 @@ protected RelationshipAttribute(string publicName, Link documentLinks, bool canI
         /// </code>
         /// </example>
         public Type Type { get; internal set; }
-        public bool IsHasMany => GetType() == typeof(HasManyAttribute);
+        public bool IsHasMany => GetType() == typeof(HasManyAttribute) || typeof(HasManyAttribute).IsAssignableFrom(GetType());
         public bool IsHasOne => GetType() == typeof(HasOneAttribute);
         public Link DocumentLinks { get; } = Link.All;
         public bool CanInclude { get; }
@@ -78,5 +78,13 @@ public override bool Equals(object obj)
         /// </summary>
         public virtual bool Is(string publicRelationshipName)
             => string.Equals(publicRelationshipName, PublicRelationshipName, StringComparison.OrdinalIgnoreCase);
+
+        /// <summary>
+        /// The internal navigation property path to the related entity.
+        /// <summary>
+        /// <remarks>
+        /// In all cases except the HasManyThrough relationships, this will just be the <see cref"InternalRelationshipName" />.
+        /// </remarks>
+        public virtual string RelationshipPath => InternalRelationshipName;
     }
 }

Diff for: test/JsonApiDotNetCoreExampleTests/Acceptance/ManyToManyTests.cs

@@ -0,0 +1,56 @@
+using System.Net;
+using System.Threading.Tasks;
+using Bogus;
+using JsonApiDotNetCore.Serialization;
+using JsonApiDotNetCoreExample.Data;
+using JsonApiDotNetCoreExample.Models;
+using Xunit;
+
+namespace JsonApiDotNetCoreExampleTests.Acceptance
+{
+    [Collection("WebHostCollection")]
+    public class ManyToManyTests
+    {
+        private static readonly Faker<Article> _articleFaker = new Faker<Article>()
+            .RuleFor(a => a.Name, f => f.Random.AlphaNumeric(10))
+            .RuleFor(a => a.Author, f => new Author());
+        private static readonly Faker<Tag> _tagFaker = new Faker<Tag>().RuleFor(a => a.Name, f => f.Random.AlphaNumeric(10));
+
+        private TestFixture<TestStartup> _fixture;
+        public ManyToManyTests(TestFixture<TestStartup> fixture) 
+        {
+            _fixture = fixture;
+        }
+
+        [Fact]
+        public async Task Can_Fetch_Many_To_Many_Through()
+        {
+            // arrange
+            var context = _fixture.GetService<AppDbContext>();
+            var article = _articleFaker.Generate();
+            var tag = _tagFaker.Generate();
+            var articleTag = new ArticleTag { 
+                Article = article,
+                Tag = tag
+            };
+            context.ArticleTags.Add(articleTag);
+            await context.SaveChangesAsync();
+            
+            var route = $"/api/v1/articles/{article.Id}?include=tags";
+
+            // act
+            var response = await _fixture.Client.GetAsync(route);
+
+            // assert
+            var body = await response.Content.ReadAsStringAsync();
+            Assert.True(HttpStatusCode.OK == response.StatusCode, $"{route} returned {response.StatusCode} status code with payload: {body}");
+            
+            var articleResponse = _fixture.GetService<IJsonApiDeSerializer>().Deserialize<Article>(body);
+            Assert.NotNull(articleResponse);
+            Assert.Equal(article.Id, articleResponse.Id);
+            
+            var tagResponse = Assert.Single(articleResponse.Tags);
+            Assert.Equal(tag.Id, tagResponse.Id);
+        }
+    }
+}