Add JSON:API sparse fieldset relationship support

The JSON:API specification allows for sparse fieldsets to limit both
attribute and relationship serialization. Until now, this library only
appliled sparse fieldset handling to attributes.

This adds relationship support.

Author: mattpolzin

lib/jsonapi/plugs/query_parser.ex

@@ -282,9 +282,9 @@ defmodule JSONAPI.QueryParser do
   @spec get_valid_fields_for_type(Config.t(), String.t()) :: list(atom())
   def get_valid_fields_for_type(%Config{view: view}, type) do
     if type == view.type() do
-      view.fields()
+      view.valid_attrs_and_rels()
     else
-      get_view_for_type(view, type).fields()
+      get_view_for_type(view, type).valid_attrs_and_rels()
     end
   end
 

lib/jsonapi/serializer.ex

@@ -81,7 +81,7 @@ defmodule JSONAPI.Serializer do
   @spec encode_relationships(Conn.t(), document(), tuple(), list()) :: tuple()
   def encode_relationships(conn, doc, {view, data, _, _} = view_info, options) do
     data
-    |> view.resource_relationships()
+    |> view.visible_relationships(conn)
     |> Enum.filter(&assoc_loaded?(Map.get(data, get_data_key(&1))))
     |> Enum.map_reduce(doc, &build_relationships(conn, view_info, &1, &2, options))
   end
@@ -314,7 +314,7 @@ defmodule JSONAPI.Serializer do
   end
 
   defp get_default_includes(view, data) do
-    rels = view.resource_relationships(data)
+    rels = view.visible_relationships(data, nil)
 
     Enum.filter(rels, &include_rel_by_default/1)
   end
@@ -326,7 +326,7 @@ defmodule JSONAPI.Serializer do
   end
 
   defp get_query_includes(view, query_includes, data) do
-    rels = view.resource_relationships(data)
+    rels = view.visible_relationships(data, nil)
 
     query_includes
     |> Enum.map(fn

lib/jsonapi/view.ex

@@ -47,6 +47,11 @@ defmodule JSONAPI.View do
   2-arity function inside the view that takes `data` and `conn` as arguments and has
   the same name as the field it will be producing. Refer to our `fullname/2` example below.
 
+  For historical reasons, the `View` module's "fields" are actually exclusively
+  attributes. That is, although JSON:API defines fields to be both attributes
+  and relationships, you should read the `View` module's macros as `field` ->
+  `attribute` and `relationship` -> `relationship`.
+
       defmodule UserView do
         use JSONAPI.View
 
@@ -233,6 +238,7 @@ defmodule JSONAPI.View do
   @callback path() :: String.t() | nil
   @callback relationships() :: resource_relationships()
   @callback polymorphic_relationships(data()) :: resource_relationships()
+  @callback visible_relationships(data(), Conn.t() | nil) :: resource_relationships()
   @callback type() :: resource_type() | nil
   @callback polymorphic_type(data()) :: resource_type() | nil
   @callback url_for(data(), Conn.t() | nil) :: String.t()
@@ -377,6 +383,10 @@ defmodule JSONAPI.View do
       def visible_fields(data, conn),
         do: View.visible_fields(__MODULE__, data, conn)
 
+      @impl View
+      def visible_relationships(data, conn),
+        do: View.visible_relationships(__MODULE__, data, conn)
+
       def resource_fields(data) do
         if @polymorphic_resource? do
           polymorphic_fields(data)
@@ -401,6 +411,24 @@ defmodule JSONAPI.View do
         end
       end
 
+      @doc """
+      Get valid attribute and relationship names (collectively known in
+      JSON:API as "fields", but the name "fields" is taken and left intact for
+      backwards compatibility).
+
+      This function can be used before knowing the data being serialized and as
+      a consequence it cannot perform polymorphic logic; this is the only way
+      to operate from the QueryParser Plug.
+      """
+      @spec valid_attrs_and_rels() :: [atom()]
+      def valid_attrs_and_rels do
+        if @polymorphic_resource? do
+          []
+        else
+          fields() ++ Enum.map(relationships(), fn {name, _} -> name end)
+        end
+      end
+
       defoverridable View
 
       def index(models, conn, _params, meta \\ nil, options \\ []),
@@ -537,6 +565,22 @@ defmodule JSONAPI.View do
     all_fields -- hidden_fields
   end
 
+  @spec visible_relationships(t(), data(), Conn.t() | nil) :: resource_relationships()
+  def visible_relationships(view, data, conn) do
+    view
+    |> requested_fields_for_type(data, conn)
+    |> net_relationships_for_type(view.resource_relationships(data))
+  end
+
+  defp net_relationships_for_type(requested_fields, relationships) when requested_fields in [nil, %{}],
+    do: relationships
+
+  defp net_relationships_for_type(requested_fields, relationships) do
+    Enum.filter(relationships, fn {name, _} ->
+      Enum.any?(requested_fields, &Kernel.==(&1, name))
+    end)
+  end
+
   defp net_fields_for_type(requested_fields, fields) when requested_fields in [nil, %{}],
     do: fields
 

test/jsonapi/plugs/query_parser_test.exs

@@ -1,8 +1,8 @@
 defmodule JSONAPI.QueryParserTest do
   use ExUnit.Case
-  use Plug.Test
 
   import JSONAPI.QueryParser
+  import Plug.{Conn, Test}
 
   alias JSONAPI.Config
   alias JSONAPI.Exceptions.InvalidQuery
@@ -153,7 +153,7 @@ defmodule JSONAPI.QueryParserTest do
     assert parse_include(config, "author,comments.user").include == [:author, {:comments, :user}]
   end
 
-  test "parse_fields/2 turns a fields map into a map of validated fields" do
+  test "parse_fields/2 turns a fields map containing an attribute into a map of validated fields" do
     config = struct(Config, view: MyView)
     assert parse_fields(config, %{"mytype" => "id,text"}).fields == %{"mytype" => [:id, :text]}
   end
@@ -163,6 +163,11 @@ defmodule JSONAPI.QueryParserTest do
     assert parse_fields(config, %{"mytype" => ""}).fields == %{"mytype" => []}
   end
 
+  test "parse_fields/2 accepts relationship fields" do
+    config = struct(Config, view: MyView)
+    assert parse_fields(config, %{"mytype" => "id,author"}).fields == %{"mytype" => [:id, :author]}
+  end
+
   test "parse_fields/2 raises on invalid parsing" do
     config = struct(Config, view: MyView)
 

test/jsonapi/serializer_test.exs

@@ -304,6 +304,32 @@ defmodule JSONAPI.SerializerTest do
     assert Enum.count(encoded[:included]) == 4
   end
 
+  test "serialize handles sparse fieldsets" do
+    data = %{
+      id: 1,
+      text: "Hello",
+      body: "Hello world",
+      author: %{id: 2, username: "jason"},
+      best_comments: [
+        %{id: 5, text: "greatest comment ever", user: %{id: 4, username: "jack"}},
+        %{id: 6, text: "not so great", user: %{id: 2, username: "jason"}}
+      ]
+    }
+
+    conn =
+      %Plug.Conn{}
+      |> Plug.Conn.fetch_query_params()
+      |> Plug.Conn.assign(:jsonapi_query, %Config{fields: %{PostView.type() => [:author, :text]}})
+
+    encoded = Serializer.serialize(PostView, data, conn)
+
+    assert is_nil(encoded[:data][:attributes][:body])
+    assert %{text: "Hello"} = encoded[:data][:attributes]
+
+    assert is_nil(encoded[:data][:relationships][:best_comments])
+    assert %{author: %{data: %{id: "2", type: "user"}}} = encoded[:data][:relationships]
+  end
+
   test "serialize handles a list" do
     data = %{
       id: 1,

test/jsonapi/view_test.exs

@@ -13,6 +13,10 @@ defmodule JSONAPI.ViewTest do
     end
 
     def hidden(_), do: []
+
+    def relationships do
+      [{:comments, JSONAPI.ViewTest.CommentView}]
+    end
   end
 
   defmodule CommentView do
@@ -41,6 +45,8 @@ defmodule JSONAPI.ViewTest do
 
   defmodule CarView do
     use JSONAPI.View, type: "cars", namespace: ""
+
+    def fields, do: []
   end
 
   defmodule DynamicView do
@@ -369,4 +375,20 @@ defmodule JSONAPI.ViewTest do
              some_other_field: "foo"
            } == PolymorphicView.attributes(data, conn)
   end
+
+  test "visible_relationships/2 returns all relationship fields by default" do
+    data = %{comments: [%{body: "hello"}]}
+    config = %JSONAPI.Config{}
+    conn = %Plug.Conn{assigns: %{jsonapi_query: config}}
+
+    assert [{:comments, CommentView}] = PostView.visible_relationships(data, conn)
+  end
+
+  test "visible_relationships/2 can omit relationships based on requested fields" do
+    data = %{body: "Chunky", title: "Bacon", comments: [%{body: "hello"}]}
+    config = %JSONAPI.Config{fields: %{PostView.type() => [:body]}}
+    conn = %Plug.Conn{assigns: %{jsonapi_query: config}}
+
+    assert [] = PostView.visible_relationships(data, conn)
+  end
 end