Feat/#151: Many-to-Many Support via [HasManyThrough]

.gitignore

@@ -1,3 +1,5 @@
+.DS_Store
+
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 

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)
+        { }
+    }
+}

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; }
@@ -53,7 +55,8 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
         public DbSet<DepartmentEntity> Departments { get; set; }
         public DbSet<CourseStudentEntity> Registrations { get; set; }
         public DbSet<StudentEntity> Students { get; set; }
-
         public DbSet<PersonRole> PersonRoles { get; set; }
+        public DbSet<ArticleTag> ArticleTags { get; set; }
+        public DbSet<Tag> Tags { get; set; }
     }
 }

src/Examples/JsonApiDotNetCoreExample/Models/Article.cs

@@ -1,3 +1,5 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
 using JsonApiDotNetCore.Models;
 
 namespace JsonApiDotNetCoreExample.Models
@@ -10,5 +12,10 @@ public class Article : Identifiable
         [HasOne("author")]
         public Author Author { get; set; }
         public int AuthorId { get; set; }
+
+        [NotMapped]
+        [HasManyThrough(nameof(ArticleTags))]
+        public List<Tag> Tags { get; set; }
+        public List<ArticleTag> ArticleTags { get; set; }
     }
 }

src/Examples/JsonApiDotNetCoreExample/Models/ArticleTag.cs

@@ -0,0 +1,11 @@
+namespace JsonApiDotNetCoreExample.Models
+{
+    public class ArticleTag
+    {
+        public int ArticleId { get; set; }
+        public Article Article { get; set; }
+
+        public int TagId { get; set; }
+        public Tag Tag { get; set; }
+    }
+}

src/Examples/JsonApiDotNetCoreExample/Models/Tag.cs

@@ -0,0 +1,9 @@
+using JsonApiDotNetCore.Models;
+
+namespace JsonApiDotNetCoreExample.Models
+{
+    public class Tag : Identifiable
+    {
+        public string Name { get; set; }
+    }
+}

src/JsonApiDotNetCore/Builders/ContextGraphBuilder.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
@@ -166,7 +167,47 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
                 attribute.InternalRelationshipName = prop.Name;
                 attribute.Type = GetRelationshipType(attribute, prop);
                 attributes.Add(attribute);
+
+                if(attribute is HasManyThroughAttribute hasManyThroughAttribute) {
+                    var throughProperty = properties.SingleOrDefault(p => p.Name == hasManyThroughAttribute.InternalThroughName);
+                    if(throughProperty == null)
+                        throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}'. Type does not contain a property named '{hasManyThroughAttribute.InternalThroughName}'.");
+
+                    if(throughProperty.PropertyType.Implements<IList>() == false)
+                        throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}.{throughProperty.Name}'. Property type does not implement IList.");
+
+                    // assumption: the property should be a generic collection, e.g. List<ArticleTag>
+                    if(throughProperty.PropertyType.IsGenericType == false)
+                        throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}'. Expected through entity to be a generic type, such as List<{prop.PropertyType}>.");
+
+                    // Article → List<ArticleTag>
+                    hasManyThroughAttribute.ThroughProperty = throughProperty;
+
+                    // ArticleTag
+                    hasManyThroughAttribute.ThroughType = throughProperty.PropertyType.GetGenericArguments()[0];
+
+                    var throughProperties = hasManyThroughAttribute.ThroughType.GetProperties();
+
+                    // ArticleTag.Article
+                    hasManyThroughAttribute.LeftProperty = throughProperties.SingleOrDefault(x => x.PropertyType == entityType)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a navigation property to type {entityType}");
+
+                    // ArticleTag.ArticleId
+                    var leftIdPropertyName = JsonApiOptions.RelatedIdMapper.GetRelatedIdPropertyName(hasManyThroughAttribute.LeftProperty.Name);
+                    hasManyThroughAttribute.LeftIdProperty = throughProperties.SingleOrDefault(x => x.Name == leftIdPropertyName)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a relationship id property to type {entityType} with name {leftIdPropertyName}");
+
+                    // Article → ArticleTag.Tag
+                    hasManyThroughAttribute.RightProperty = throughProperties.SingleOrDefault(x => x.PropertyType == hasManyThroughAttribute.Type)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a navigation property to type {hasManyThroughAttribute.Type}");
+
+                    // ArticleTag.TagId
+                    var rightIdPropertyName = JsonApiOptions.RelatedIdMapper.GetRelatedIdPropertyName(hasManyThroughAttribute.RightProperty.Name);
+                    hasManyThroughAttribute.RightIdProperty = throughProperties.SingleOrDefault(x => x.Name == rightIdPropertyName)
+                        ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a relationship id property to type {hasManyThroughAttribute.Type} with name {rightIdPropertyName}");
+                }
             }
+
             return attributes;
         }
 

src/JsonApiDotNetCore/Builders/DocumentBuilder.cs

@@ -18,8 +18,8 @@ public class DocumentBuilder : IDocumentBuilder
         private readonly IScopedServiceProvider _scopedServiceProvider;
 
         public DocumentBuilder(
-            IJsonApiContext jsonApiContext, 
-            IRequestMeta requestMeta = null, 
+            IJsonApiContext jsonApiContext,
+            IRequestMeta requestMeta = null,
             IDocumentBuilderOptionsProvider documentBuilderOptionsProvider = null,
             IScopedServiceProvider scopedServiceProvider = null)
         {
@@ -112,7 +112,8 @@ public ResourceObject GetData(ContextEntity contextEntity, IIdentifiable entity)
 
         public ResourceObject GetData(ContextEntity contextEntity, IIdentifiable entity, IResourceDefinition resourceDefinition = null)
         {
-            var data = new ResourceObject {
+            var data = new ResourceObject
+            {
                 Type = contextEntity.EntityName,
                 Id = entity.StringId
             };
@@ -178,7 +179,7 @@ private RelationshipData GetRelationshipData(RelationshipAttribute attr, Context
             }
 
             // this only includes the navigation property, we need to actually check the navigation property Id
-            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationship(entity, attr.InternalRelationshipName);
+            var navigationEntity = _jsonApiContext.ContextGraph.GetRelationshipValue(entity, attr);
             if (navigationEntity == null)
                 relationshipData.SingleData = attr.IsHasOne
                     ? GetIndependentRelationshipIdentifier((HasOneAttribute)attr, entity)
@@ -195,14 +196,14 @@ private List<ResourceObject> GetIncludedEntities(List<ResourceObject> included,
         {
             if (_jsonApiContext.IncludedRelationships != null)
             {
-                foreach(var relationshipName in _jsonApiContext.IncludedRelationships)
+                foreach (var relationshipName in _jsonApiContext.IncludedRelationships)
                 {
                     var relationshipChain = relationshipName.Split('.');
 
                     var contextEntity = rootContextEntity;
                     var entity = rootResource;
                     included = IncludeRelationshipChain(included, rootContextEntity, rootResource, relationshipChain, 0);
-                }                
+                }
             }
 
             return included;
@@ -234,15 +235,15 @@ private List<ResourceObject> IncludeRelationshipChain(
         private List<ResourceObject> IncludeSingleResourceRelationships(
             List<ResourceObject> included, IIdentifiable navigationEntity, RelationshipAttribute relationship, string[] relationshipChain, int relationshipChainIndex)
         {
-            if (relationshipChainIndex < relationshipChain.Length) 
+            if (relationshipChainIndex < relationshipChain.Length)
             {
                 var nextContextEntity = _jsonApiContext.ContextGraph.GetContextEntity(relationship.Type);
                 var resource = (IIdentifiable)navigationEntity;
                 // recursive call
-                if(relationshipChainIndex < relationshipChain.Length - 1)
+                if (relationshipChainIndex < relationshipChain.Length - 1)
                     included = IncludeRelationshipChain(included, nextContextEntity, resource, relationshipChain, relationshipChainIndex + 1);
             }
-            
+
             return included;
         }
 
@@ -284,16 +285,18 @@ 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)
             {
+                // this method makes the assumption that entities is a homogenous collection
+                // so, we just lookup the type of the first entity on the graph
+                // this is better than trying to get it from the generic parameter since it could
+                // be less specific than what is registered on the graph (e.g. IEnumerable<object>) 
+                typeName = typeName ?? _jsonApiContext.ContextGraph.GetContextEntity(entity.GetType()).EntityName;
                 relationships.Add(new ResourceIdentifierObject
                 {
-                    Type = typeName.EntityName,
+                    Type = typeName,
                     Id = ((IIdentifiable)entity).StringId
                 });
             }
@@ -305,7 +308,7 @@ private ResourceIdentifierObject GetRelationship(object entity)
             var objType = entity.GetType();
             var contextEntity = _jsonApiContext.ContextGraph.GetContextEntity(objType);
 
-            if(entity is IIdentifiable identifiableEntity)
+            if (entity is IIdentifiable identifiableEntity)
                 return new ResourceIdentifierObject
                 {
                     Type = contextEntity.EntityName,

src/JsonApiDotNetCore/Configuration/JsonApiOptions.cs

@@ -22,6 +22,11 @@ public class JsonApiOptions
         /// </summary>
         public static IResourceNameFormatter ResourceNameFormatter { get; set; } = new DefaultResourceNameFormatter();
 
+        /// <summary>
+        /// Provides an interface for formatting relationship id properties given the navigation property name
+        /// </summary>
+        public static IRelatedIdMapper RelatedIdMapper { get; set; } = new DefaultRelatedIdMapper();
+
         /// <summary>
         /// Whether or not stack traces should be serialized in Error objects
         /// </summary>

src/JsonApiDotNetCore/Data/DefaultEntityRepository.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
@@ -143,17 +144,17 @@ public virtual async Task<TEntity> GetAndIncludeAsync(TId id, string relationshi
         /// <inheritdoc />
         public virtual async Task<TEntity> CreateAsync(TEntity entity)
         {
-            AttachRelationships();
+            AttachRelationships(entity);
             _dbSet.Add(entity);
 
             await _context.SaveChangesAsync();
 
             return entity;
         }
 
-        protected virtual void AttachRelationships()
+        protected virtual void AttachRelationships(TEntity entity = null)
         {
-            AttachHasManyPointers();
+            AttachHasManyPointers(entity);
             AttachHasOnePointers();
         }
 
@@ -183,15 +184,42 @@ public void DetachRelationshipPointers(TEntity entity)
         /// This is used to allow creation of HasMany relationships when the
         /// dependent side of the relationship already exists.
         /// </summary>
-        private void AttachHasManyPointers()
+        private void AttachHasManyPointers(TEntity entity)
         {
             var relationships = _jsonApiContext.HasManyRelationshipPointers.Get();
             foreach (var relationship in relationships)
             {
-                foreach (var pointer in relationship.Value)
-                {
-                    _context.Entry(pointer).State = EntityState.Unchanged;
-                }
+                if(relationship.Key is HasManyThroughAttribute hasManyThrough)
+                    AttachHasManyThrough(entity, hasManyThrough, relationship.Value);
+                else
+                    AttachHasMany(relationship.Key as HasManyAttribute, relationship.Value);                
+            }
+        }
+
+        private void AttachHasMany(HasManyAttribute relationship, IList pointers)
+        {
+            foreach (var pointer in pointers)
+                _context.Entry(pointer).State = EntityState.Unchanged;
+        }
+
+        private void AttachHasManyThrough(TEntity entity, HasManyThroughAttribute hasManyThrough, IList pointers)
+        {
+            // create the collection (e.g. List<ArticleTag>)
+            // this type MUST implement IList so we can build the collection
+            // if this is problematic, we _could_ reflect on the type and find an Add method
+            // or we might be able to create a proxy type and implement the enumerator
+            var throughRelationshipCollection = Activator.CreateInstance(hasManyThrough.ThroughProperty.PropertyType) as IList;
+            hasManyThrough.ThroughProperty.SetValue(entity, throughRelationshipCollection);
+
+            foreach (var pointer in pointers)
+            {
+                _context.Entry(pointer).State = EntityState.Unchanged;
+                var throughInstance = Activator.CreateInstance(hasManyThrough.ThroughType);
+
+                hasManyThrough.LeftProperty.SetValue(throughInstance, entity);
+                hasManyThrough.RightProperty.SetValue(throughInstance, pointer);
+
+                throughRelationshipCollection.Add(throughInstance);
             }
         }
 
@@ -221,6 +249,8 @@ public virtual async Task<TEntity> UpdateAsync(TId id, TEntity entity)
             foreach (var relationship in _jsonApiContext.RelationshipsToUpdate)
                 relationship.Key.SetValue(oldEntity, relationship.Value);
 
+            AttachRelationships(oldEntity);
+
             await _context.SaveChangesAsync();
 
             return oldEntity;
@@ -229,7 +259,15 @@ public virtual async Task<TEntity> UpdateAsync(TId id, TEntity entity)
         /// <inheritdoc />
         public async Task UpdateRelationshipsAsync(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds)
         {
-            var genericProcessor = _genericProcessorFactory.GetProcessor<IGenericProcessor>(typeof(GenericProcessor<>), relationship.Type);
+            // TODO: it would be better to let this be determined within the relationship attribute...
+            // need to think about the right way to do that since HasMany doesn't need to think about this
+            // and setting the HasManyThrough.Type to the join type (ArticleTag instead of Tag) for this changes the semantics
+            // of the property...
+            var typeToUpdate = (relationship is HasManyThroughAttribute hasManyThrough)
+                ? hasManyThrough.ThroughType
+                : relationship.Type;
+
+            var genericProcessor = _genericProcessorFactory.GetProcessor<IGenericProcessor>(typeof(GenericProcessor<>), typeToUpdate);
             await genericProcessor.UpdateRelationshipsAsync(parent, relationship, relationshipIds);
         }
 
@@ -275,8 +313,8 @@ 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);