fix(JsonApiDeserializer): if hasOne is nullable allow it to be set null

Author: jaredcnance

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

@@ -39,9 +39,14 @@ public HasOneAttribute(string publicName, Link documentLinks = Link.All, bool ca
             ? $"{InternalRelationshipName}Id"
             : _explicitIdentifiablePropertyName;
 
+        /// <summary>
+        /// Sets the value of the property identified by this attribute
+        /// </summary>
+        /// <param name="entity">The target object</param>
+        /// <param name="newValue">The new property value</param>
         public override void SetValue(object entity, object newValue)
         {
-            var propertyName = (newValue.GetType() == Type)
+            var propertyName = (newValue?.GetType() == Type)
                 ? InternalRelationshipName
                 : IdentifiablePropertyName;
 

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

@@ -19,6 +19,28 @@ protected RelationshipAttribute(string publicName, Link documentLinks, bool canI
         public Link DocumentLinks { get; } = Link.All;
         public bool CanInclude { get; }
 
+        public bool TryGetHasOne(out HasOneAttribute result)
+        {
+            if (IsHasOne)
+            {
+                result = (HasOneAttribute)this;
+                return true;
+            }
+            result = null;
+            return false;
+        }
+
+        public bool TryGetHasMany(out HasManyAttribute result)
+        {
+            if (IsHasMany)
+            {
+                result = (HasManyAttribute)this;
+                return true;
+            }
+            result = null;
+            return false;
+        }
+
         public abstract void SetValue(object entity, object newValue);
 
         public override string ToString()

Diff for: src/JsonApiDotNetCore/Serialization/JsonApiDeSerializer.cs

@@ -207,15 +207,17 @@ private object SetHasOneRelationship(object entity,
 
                 var rio = (ResourceIdentifierObject)relationshipData.ExposedData;
 
-                if (rio == null) return entity;
-
-                var newValue = rio.Id;
-
                 var foreignKey = attr.IdentifiablePropertyName;
                 var entityProperty = entityProperties.FirstOrDefault(p => p.Name == foreignKey);
                 if (entityProperty == null)
                     throw new JsonApiException(400, $"{contextEntity.EntityType.Name} does not contain a foreign key property '{foreignKey}' for has one relationship '{attr.InternalRelationshipName}'");
 
+                // e.g. PATCH /articles
+                // {... { "relationships":{ "Owner": { "data" :null } } } }
+                if (rio == null && Nullable.GetUnderlyingType(entityProperty.PropertyType) == null)
+                    throw new JsonApiException(400, $"Cannot set required relationship identifier '{attr.IdentifiablePropertyName}' to null.");
+
+                var newValue = rio?.Id ?? null;
                 var convertedValue = TypeHelper.ConvertType(newValue, entityProperty.PropertyType);
 
                 _jsonApiContext.RelationshipsToUpdate[relationshipAttr] = convertedValue;

Diff for: src/JsonApiDotNetCore/Services/EntityResourceService.cs

@@ -133,7 +133,7 @@ public virtual async Task UpdateRelationshipsAsync(TId id, string relationshipNa
                 .Relationships
                 .FirstOrDefault(r => r.InternalRelationshipName == relationshipName);
 
-            var relationshipIds = relationships.Select(r => r.Id?.ToString());
+            var relationshipIds = relationships.Select(r => r?.Id?.ToString());
 
             await _entities.UpdateRelationshipsAsync(entity, relationship, relationshipIds);
         }

Diff for: test/JsonApiDotNetCoreExampleTests/Acceptance/Spec/UpdatingRelationshipsTests.cs

@@ -127,5 +127,100 @@ public async Task Can_Update_ToOne_Relationship_ThroughLink()
             Assert.Equal(HttpStatusCode.OK, response.StatusCode);
             Assert.NotNull(todoItemsOwner);
         }
+
+        [Fact]
+        public async Task Can_Delete_Relationship_By_Patching_Resource()
+        {
+            // arrange
+            var person = _personFaker.Generate();
+            var todoItem = _todoItemFaker.Generate();
+            todoItem.Owner = person;
+
+            _context.People.Add(person);
+            _context.TodoItems.Add(todoItem);
+            _context.SaveChanges();
+
+            var builder = new WebHostBuilder()
+                .UseStartup<Startup>();
+
+            var server = new TestServer(builder);
+            var client = server.CreateClient();
+
+            var content = new
+            {
+                data = new
+                {
+                    type = "todo-items",
+                    relationships = new
+                    {
+                        owner = new
+                        {
+                            data = (object)null
+                        }
+                    }
+                }
+            };
+
+            var httpMethod = new HttpMethod("PATCH");
+            var route = $"/api/v1/todo-items/{todoItem.Id}";
+            var request = new HttpRequestMessage(httpMethod, route);
+            request.Content = new StringContent(JsonConvert.SerializeObject(content));
+            request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/vnd.api+json");
+
+            // Act
+            var response = await client.SendAsync(request);
+
+            // Assert
+            var todoItemResult = _context.TodoItems
+                .AsNoTracking()
+                .Include(t => t.Owner)
+                .Single(t => t.Id == todoItem.Id);
+
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            Assert.Null(todoItemResult.Owner);
+        }
+
+        [Fact]
+        public async Task Can_Delete_Relationship_By_Patching_Relationship()
+        {
+            // arrange
+            var person = _personFaker.Generate();
+            var todoItem = _todoItemFaker.Generate();
+            todoItem.Owner = person;
+
+            _context.People.Add(person);
+            _context.TodoItems.Add(todoItem);
+            _context.SaveChanges();
+
+            var builder = new WebHostBuilder()
+                .UseStartup<Startup>();
+
+            var server = new TestServer(builder);
+            var client = server.CreateClient();
+
+            var content = new
+            {
+                data = (object)null
+            };
+
+            var httpMethod = new HttpMethod("PATCH");
+            var route = $"/api/v1/todo-items/{todoItem.Id}/relationships/owner";
+            var request = new HttpRequestMessage(httpMethod, route);
+
+            request.Content = new StringContent(JsonConvert.SerializeObject(content));
+            request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/vnd.api+json");
+
+            // Act
+            var response = await client.SendAsync(request);
+
+            // Assert
+            var todoItemResult = _context.TodoItems
+                .AsNoTracking()
+                .Include(t => t.Owner)
+                .Single(t => t.Id == todoItem.Id);
+
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            Assert.Null(todoItemResult.Owner);
+        }
     }
 }