Flexible collection types/interfaces on HasManyThrough attributes

Author: Bart Koelman

src/Examples/JsonApiDotNetCoreExample/Models/Article.cs

@@ -15,13 +15,12 @@ public sealed class Article : Identifiable
 
         [NotMapped]
         [HasManyThrough(nameof(ArticleTags))]
-        public List<Tag> Tags { get; set; }
-        public List<ArticleTag> ArticleTags { get; set; }
-
+        public ISet<Tag> Tags { get; set; }
+        public ISet<ArticleTag> ArticleTags { get; set; }
 
         [NotMapped]
         [HasManyThrough(nameof(IdentifiableArticleTags))]
-        public List<Tag> IdentifiableTags { get; set; }
-        public List<IdentifiableArticleTag> IdentifiableArticleTags { get; set; }
+        public ISet<Tag> IdentifiableTags { get; set; }
+        public ISet<IdentifiableArticleTag> IdentifiableArticleTags { get; set; }
     }
 }

src/JsonApiDotNetCore/Builders/ResourceGraphBuilder.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
@@ -136,22 +135,19 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
 
                 if (attribute is HasManyThroughAttribute hasManyThroughAttribute)
                 {
-                    var throughProperty = properties.SingleOrDefault(p => p.Name == hasManyThroughAttribute.InternalThroughName);
+                    var throughProperty = properties.SingleOrDefault(p => p.Name == hasManyThroughAttribute.ThroughPropertyName);
                     if (throughProperty == null)
-                        throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}'. Type does not contain a property named '{hasManyThroughAttribute.InternalThroughName}'.");
+                        throw new JsonApiSetupException($"Invalid {nameof(HasManyThroughAttribute)} on '{entityType}.{attribute.PropertyInfo.Name}': Resource does not contain a property named '{hasManyThroughAttribute.ThroughPropertyName}'.");
 
-                    if (throughProperty.PropertyType.Implements<IList>() == false)
-                        throw new JsonApiSetupException($"Invalid '{nameof(HasManyThroughAttribute)}' on type '{entityType}.{throughProperty.Name}'. Property type does not implement IList.");
+                    var throughType = TryGetManyThroughType(throughProperty);
+                    if (throughType == null)
+                        throw new JsonApiSetupException($"Invalid {nameof(HasManyThroughAttribute)} on '{entityType}.{attribute.PropertyInfo.Name}': Referenced property '{throughProperty.Name}' does not implement 'ICollection<T>'.");
 
-                    // 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>
+                    // ICollection<ArticleTag>
                     hasManyThroughAttribute.ThroughProperty = throughProperty;
 
                     // ArticleTag
-                    hasManyThroughAttribute.ThroughType = throughProperty.PropertyType.GetGenericArguments()[0];
+                    hasManyThroughAttribute.ThroughType = throughType;
 
                     var throughProperties = hasManyThroughAttribute.ThroughType.GetProperties();
 
@@ -164,7 +160,7 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
                     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
+                    // ArticleTag.Tag
                     hasManyThroughAttribute.RightProperty = throughProperties.SingleOrDefault(x => x.PropertyType == hasManyThroughAttribute.RightType)
                         ?? throw new JsonApiSetupException($"{hasManyThroughAttribute.ThroughType} does not contain a navigation property to type {hasManyThroughAttribute.RightType}");
 
@@ -178,6 +174,24 @@ protected virtual List<RelationshipAttribute> GetRelationships(Type entityType)
             return attributes;
         }
 
+        private static Type TryGetManyThroughType(PropertyInfo throughProperty)
+        {
+            if (throughProperty.PropertyType.IsGenericType)
+            {
+                var typeArguments = throughProperty.PropertyType.GetGenericArguments();
+                if (typeArguments.Length == 1)
+                {
+                    var constructedThroughType = typeof(ICollection<>).MakeGenericType(typeArguments[0]);
+                    if (throughProperty.PropertyType.Implements(constructedThroughType))
+                    {
+                        return typeArguments[0];
+                    }
+                }
+            }
+
+            return null;
+        }
+
         protected virtual Type GetRelationshipType(RelationshipAttribute relation, PropertyInfo prop) =>
             relation is HasOneAttribute ? prop.PropertyType : prop.PropertyType.GetGenericArguments()[0];
 

src/JsonApiDotNetCore/Data/DefaultResourceRepository.cs

@@ -423,7 +423,7 @@ protected void LoadCurrentRelationships(TResource oldEntity, RelationshipAttribu
         {
             if (relationshipAttribute is HasManyThroughAttribute throughAttribute)
             {
-                _context.Entry(oldEntity).Collection(throughAttribute.InternalThroughName).Load();
+                _context.Entry(oldEntity).Collection(throughAttribute.ThroughProperty.Name).Load();
             }
             else if (relationshipAttribute is HasManyAttribute hasManyAttribute)
             {

src/JsonApiDotNetCore/Extensions/TypeExtensions.cs

@@ -108,7 +108,7 @@ public static bool Implements<T>(this Type concreteType)
         /// <summary>
         /// Whether or not a type implements an interface.
         /// </summary>
-        private static bool Implements(this Type concreteType, Type interfaceType) 
+        public static bool Implements(this Type concreteType, Type interfaceType) 
             => interfaceType?.IsAssignableFrom(concreteType) == true;
 
         /// <summary>

src/JsonApiDotNetCore/Hooks/Traversal/RelationshipProxy.cs

@@ -19,7 +19,6 @@ namespace JsonApiDotNetCore.Hooks
     /// </summary>
     internal sealed class RelationshipProxy
     {
-        private readonly bool _isHasManyThrough;
         private readonly bool _skipJoinTable;
 
         /// <summary>
@@ -40,7 +39,6 @@ public RelationshipProxy(RelationshipAttribute attr, Type relatedType, bool isCo
             IsContextRelation = isContextRelation;
             if (attr is HasManyThroughAttribute throughAttr)
             {
-                _isHasManyThrough = true;
                 _skipJoinTable |= RightType != throughAttr.ThroughType;
             }
         }
@@ -54,23 +52,23 @@ public RelationshipProxy(RelationshipAttribute attr, Type relatedType, bool isCo
         /// <param name="entity">Parent entity.</param>
         public object GetValue(IIdentifiable entity)
         {
-            if (_isHasManyThrough)
+            if (Attribute is HasManyThroughAttribute hasManyThrough)
             {
-                var throughAttr = (HasManyThroughAttribute)Attribute;
                 if (!_skipJoinTable)
                 {
-                    return throughAttr.ThroughProperty.GetValue(entity);
+                    return hasManyThrough.ThroughProperty.GetValue(entity);
                 }
                 var collection = new List<IIdentifiable>();
-                var joinEntities = (IEnumerable)throughAttr.ThroughProperty.GetValue(entity);
+                var joinEntities = (IEnumerable)hasManyThrough.ThroughProperty.GetValue(entity);
                 if (joinEntities == null) return null;
 
                 foreach (var joinEntity in joinEntities)
                 {
-                    var rightEntity = (IIdentifiable)throughAttr.RightProperty.GetValue(joinEntity);
+                    var rightEntity = (IIdentifiable)hasManyThrough.RightProperty.GetValue(joinEntity);
                     if (rightEntity == null) continue;
                     collection.Add(rightEntity);
                 }
+
                 return collection;
             }
             return Attribute.GetValue(entity);
@@ -85,30 +83,31 @@ public object GetValue(IIdentifiable entity)
         /// <param name="value">The relationship value.</param>
         public void SetValue(IIdentifiable entity, object value)
         {
-            if (_isHasManyThrough)
+            if (Attribute is HasManyThroughAttribute hasManyThrough)
             {
                 if (!_skipJoinTable)
                 {
-                    var list = (IEnumerable<object>)value;
-                    ((HasManyThroughAttribute)Attribute).ThroughProperty.SetValue(entity, list.CopyToList(RightType));
+                    hasManyThrough.ThroughProperty.SetValue(entity, value);
                     return;
                 }
-                var throughAttr = (HasManyThroughAttribute)Attribute;
-                var joinEntities = (IEnumerable<object>)throughAttr.ThroughProperty.GetValue(entity);
+
+                var joinEntities = (IEnumerable)hasManyThrough.ThroughProperty.GetValue(entity);
 
                 var filteredList = new List<object>();
-                var rightEntities = ((IEnumerable<object>)value).CopyToList(RightType);
-                foreach (var je in joinEntities)
+                var rightEntities = ((IEnumerable)value).CopyToList(RightType);
+                foreach (var joinEntity in joinEntities)
                 {
-
-                    if (((IList)rightEntities).Contains(throughAttr.RightProperty.GetValue(je)))
+                    if (((IList)rightEntities).Contains(hasManyThrough.RightProperty.GetValue(joinEntity)))
                     {
-                        filteredList.Add(je);
+                        filteredList.Add(joinEntity);
                     }
                 }
-                throughAttr.ThroughProperty.SetValue(entity, filteredList.CopyToList(throughAttr.ThroughType));
+
+                var collectionValue = filteredList.CopyToTypedCollection(hasManyThrough.ThroughProperty.PropertyType);
+                hasManyThrough.ThroughProperty.SetValue(entity, collectionValue);
                 return;
             }
+
             Attribute.SetValue(entity, value);
         }
     }

src/JsonApiDotNetCore/Models/Annotation/HasManyThroughAttribute.cs

@@ -11,7 +11,7 @@ namespace JsonApiDotNetCore.Models
 {
     /// <summary>
     /// Create a HasMany relationship through a many-to-many join relationship.
-    /// This type can only be applied on types that implement IList.
+    /// This type can only be applied on types that implement ICollection.
     /// </summary>
     /// 
     /// <example>
@@ -22,8 +22,8 @@ namespace JsonApiDotNetCore.Models
     /// <code>
     /// [NotMapped]
     /// [HasManyThrough("tags", nameof(ArticleTags))]
-    /// public List&lt;Tag&gt; Tags { get; set; }
-    /// public List&lt;ArticleTag&gt; ArticleTags { get; set; }
+    /// public ICollection&lt;Tag&gt; Tags { get; set; }
+    /// public ICollection&lt;ArticleTag&gt; ArticleTags { get; set; }
     /// </code>
     /// </example>
     [AttributeUsage(AttributeTargets.Property)]
@@ -34,39 +34,39 @@ public sealed class HasManyThroughAttribute : HasManyAttribute
         /// The public name exposed through the API will be based on the configured convention.
         /// </summary>
         /// 
-        /// <param name="internalThroughName">The name of the navigation property that will be used to get the HasMany relationship</param>
+        /// <param name="throughPropertyName">The name of the navigation property that will be used to get the HasMany relationship</param>
         /// <param name="relationshipLinks">Which links are available. Defaults to <see cref="Link.All"/></param>
         /// <param name="canInclude">Whether or not this relationship can be included using the <c>?include=public-name</c> query string</param>
         /// 
         /// <example>
         /// <code>
-        /// [HasManyThrough(nameof(ArticleTags), documentLinks: Link.All, canInclude: true)]
+        /// [HasManyThrough(nameof(ArticleTags), relationshipLinks: Link.All, canInclude: true)]
         /// </code>
         /// </example>
-        public HasManyThroughAttribute(string internalThroughName, Link relationshipLinks = Link.All, bool canInclude = true)
+        public HasManyThroughAttribute(string throughPropertyName, Link relationshipLinks = Link.All, bool canInclude = true)
         : base(null, relationshipLinks, canInclude)
         {
-            InternalThroughName = internalThroughName;
+            ThroughPropertyName = throughPropertyName;
         }
 
         /// <summary>
         /// Create a HasMany relationship through a many-to-many join relationship.
         /// </summary>
         /// 
         /// <param name="publicName">The relationship name as exposed by the API</param>
-        /// <param name="internalThroughName">The name of the navigation property that will be used to get the HasMany relationship</param>
-        /// <param name="documentLinks">Which links are available. Defaults to <see cref="Link.All"/></param>
+        /// <param name="throughPropertyName">The name of the navigation property that will be used to get the HasMany relationship</param>
+        /// <param name="relationshipLinks">Which links are available. Defaults to <see cref="Link.All"/></param>
         /// <param name="canInclude">Whether or not this relationship can be included using the <c>?include=public-name</c> query string</param>
         /// 
         /// <example>
         /// <code>
-        /// [HasManyThrough("tags", nameof(ArticleTags), documentLinks: Link.All, canInclude: true)]
+        /// [HasManyThrough("tags", nameof(ArticleTags), relationshipLinks: Link.All, canInclude: true)]
         /// </code>
         /// </example>
-        public HasManyThroughAttribute(string publicName, string internalThroughName, Link documentLinks = Link.All, bool canInclude = true)
-        : base(publicName, documentLinks, canInclude)
+        public HasManyThroughAttribute(string publicName, string throughPropertyName, Link relationshipLinks = Link.All, bool canInclude = true)
+        : base(publicName, relationshipLinks, canInclude)
         {
-            InternalThroughName = internalThroughName;
+            ThroughPropertyName = throughPropertyName;
         }
 
         /// <summary>
@@ -78,7 +78,7 @@ public override object GetValue(object entity)
         {
             var throughNavigationProperty = entity.GetType()
                 .GetProperties()
-                .Single(p => p.Name == InternalThroughName);
+                .Single(p => p.Name == ThroughProperty.Name);
 
             var throughEntities = throughNavigationProperty.GetValue(entity);
 
@@ -105,16 +105,17 @@ public override void SetValue(object entity, object newValue)
             }
             else
             {
-                var throughRelationshipCollection = ThroughProperty.PropertyType.New<IList>();
-                ThroughProperty.SetValue(entity, throughRelationshipCollection);
-
-                foreach (IIdentifiable pointer in (IList)newValue)
+                List<object> instances = new List<object>();
+                foreach (IIdentifiable resource in (IEnumerable)newValue)
                 {
-                    var throughInstance = ThroughType.New();
+                    object throughInstance = ThroughType.New();
                     LeftProperty.SetValue(throughInstance, entity);
-                    RightProperty.SetValue(throughInstance, pointer);
-                    throughRelationshipCollection.Add(throughInstance);
+                    RightProperty.SetValue(throughInstance, resource);
+                    instances.Add(throughInstance);
                 }
+
+                var typedCollection = instances.CopyToTypedCollection(ThroughProperty.PropertyType);
+                ThroughProperty.SetValue(entity, typedCollection);
             }
         }
 
@@ -125,7 +126,7 @@ public override void SetValue(object entity, object newValue)
         /// In the `[HasManyThrough("tags", nameof(ArticleTags))]` example
         /// this would be "ArticleTags".
         /// </example>
-        public string InternalThroughName { get; }
+        internal string ThroughPropertyName { get; }
 
         /// <summary>
         /// The join type.
@@ -205,7 +206,7 @@ public override void SetValue(object entity, object newValue)
         /// this would point to the `Article.ArticleTags` property
         ///
         /// <code>
-        /// public List&lt;ArticleTags&gt; ArticleTags { get; set; }
+        /// public ICollection&lt;ArticleTags&gt; ArticleTags { get; set; }
         /// </code>
         ///
         /// </example>
@@ -215,6 +216,6 @@ public override void SetValue(object entity, object newValue)
         /// <example>
         /// "ArticleTags.Tag"
         /// </example>
-        public override string RelationshipPath => $"{InternalThroughName}.{RightProperty.Name}";
+        public override string RelationshipPath => $"{ThroughProperty.Name}.{RightProperty.Name}";
     }
 }

test/UnitTests/ResourceHooks/ResourceHookExecutor/ManyToMany_OnReturnTests.cs

@@ -16,7 +16,7 @@ public sealed class ManyToMany_OnReturnTests : HooksTestsSetup
             var tagsSubset = _tagFaker.Generate(3);
             var joinsSubSet = _articleTagFaker.Generate(3);
             var articleTagsSubset = _articleFaker.Generate();
-            articleTagsSubset.ArticleTags = joinsSubSet;
+            articleTagsSubset.ArticleTags = joinsSubSet.ToHashSet();
             for (int i = 0; i < 3; i++)
             {
                 joinsSubSet[i].Article = articleTagsSubset;
@@ -27,7 +27,7 @@ public sealed class ManyToMany_OnReturnTests : HooksTestsSetup
             var completeJoin = _articleTagFaker.Generate(6);
 
             var articleWithAllTags = _articleFaker.Generate();
-            articleWithAllTags.ArticleTags = completeJoin;
+            articleWithAllTags.ArticleTags = completeJoin.ToHashSet();
 
             for (int i = 0; i < 6; i++)
             {

test/UnitTests/ResourceHooks/ResourceHooksTestsSetup.cs

@@ -86,7 +86,7 @@ protected HashSet<TodoItem> CreateTodoWithOwner()
             var tagsSubset = _tagFaker.Generate(3);
             var joinsSubSet = _articleTagFaker.Generate(3);
             var articleTagsSubset = _articleFaker.Generate();
-            articleTagsSubset.ArticleTags = joinsSubSet;
+            articleTagsSubset.ArticleTags = joinsSubSet.ToHashSet();
             for (int i = 0; i < 3; i++)
             {
                 joinsSubSet[i].Article = articleTagsSubset;
@@ -97,7 +97,7 @@ protected HashSet<TodoItem> CreateTodoWithOwner()
             var completeJoin = _articleTagFaker.Generate(6);
 
             var articleWithAllTags = _articleFaker.Generate();
-            articleWithAllTags.ArticleTags = completeJoin;
+            articleWithAllTags.ArticleTags = completeJoin.ToHashSet();
 
             for (int i = 0; i < 6; i++)
             {
@@ -116,7 +116,7 @@ protected HashSet<TodoItem> CreateTodoWithOwner()
             var tagsSubset = _tagFaker.Generate(3);
             var joinsSubSet = _identifiableArticleTagFaker.Generate(3);
             var articleTagsSubset = _articleFaker.Generate();
-            articleTagsSubset.IdentifiableArticleTags = joinsSubSet;
+            articleTagsSubset.IdentifiableArticleTags = joinsSubSet.ToHashSet();
             for (int i = 0; i < 3; i++)
             {
                 joinsSubSet[i].Article = articleTagsSubset;
@@ -126,7 +126,7 @@ protected HashSet<TodoItem> CreateTodoWithOwner()
             var completeJoin = _identifiableArticleTagFaker.Generate(6);
 
             var articleWithAllTags = _articleFaker.Generate();
-            articleWithAllTags.IdentifiableArticleTags = joinsSubSet;
+            articleWithAllTags.IdentifiableArticleTags = joinsSubSet.ToHashSet();
 
             for (int i = 0; i < 6; i++)
             {