Format required checks for relationships

lib/jsonapi/error_view.ex

@@ -5,6 +5,7 @@ defmodule JSONAPI.ErrorView do
   import Plug.Conn, only: [send_resp: 3, halt: 1, put_resp_content_type: 2]
 
   @crud_message "Check out http://jsonapi.org/format/#crud for more info."
+  @relationship_resource_linkage_message "Check out https://jsonapi.org/format/#document-resource-object-linkage for more info."
 
   @spec build_error(binary(), pos_integer(), binary() | nil, binary() | nil) :: map()
   def build_error(title, status, detail, pointer \\ nil, meta \\ nil) do
@@ -93,12 +94,57 @@ defmodule JSONAPI.ErrorView do
     |> serialize_error
   end
 
+  @spec relationships_missing_object :: map()
+  def relationships_missing_object do
+    "Relationships parameter is not an object"
+    |> build_error(
+      400,
+      "Check out https://jsonapi.org/format/#document-resource-object-relationships for more info.",
+      "/data/relationships"
+    )
+    |> serialize_error
+  end
+
+  @spec missing_relationship_data_param_error(binary()) :: map()
+  def missing_relationship_data_param_error(relationship_name) do
+    "Missing data member in relationship"
+    |> build_error(
+      400,
+      "Check out https://jsonapi.org/format/#crud-creating and https://jsonapi.org/format/#crud-updating-resource-relationships for more info.",
+      "/data/relationships/#{relationship_name}/data"
+    )
+  end
+
+  @spec missing_relationship_data_id_param_error(binary()) :: map()
+  def missing_relationship_data_id_param_error(relationship_name) do
+    "Missing id in relationship data parameter"
+    |> build_error(
+      400,
+      @relationship_resource_linkage_message,
+      "/data/relationships/#{relationship_name}/data/id"
+    )
+  end
+
+  @spec missing_relationship_data_type_param_error(binary()) :: map()
+  def missing_relationship_data_type_param_error(relationship_name) do
+    "Missing type in relationship data parameter"
+    |> build_error(
+      400,
+      @relationship_resource_linkage_message,
+      "/data/relationships/#{relationship_name}/data/type"
+    )
+  end
+
   @spec send_error(Plug.Conn.t(), term()) :: term()
   def send_error(conn, %{errors: [%{status: status}]} = error),
     do: send_error(conn, status, error)
 
   def send_error(conn, %{errors: errors} = error) when is_list(errors) do
-    status = Enum.max_by(errors, &Map.get(&1, :status))
+    status =
+      errors
+      |> Enum.max_by(&Map.get(&1, :status))
+      |> Map.get(:status)
+
     send_error(conn, status, error)
   end
 
@@ -122,10 +168,20 @@ defmodule JSONAPI.ErrorView do
 
   @spec serialize_error(map()) :: map()
   def serialize_error(error) do
-    error = Map.take(error, [:detail, :id, :links, :meta, :source, :status, :title])
+    error = extract_error(error)
     %{errors: [error]}
   end
 
+  @spec serialize_errors(list()) :: map()
+  def serialize_errors(errors) do
+    extracted = Enum.map(errors, &extract_error/1)
+    %{errors: extracted}
+  end
+
+  defp extract_error(error) do
+    Map.take(error, [:detail, :id, :links, :meta, :source, :status, :title])
+  end
+
   defp append_field(error, _field, nil), do: error
   defp append_field(error, :meta, value), do: Map.put(error, :meta, %{meta: value})
   defp append_field(error, :source, value), do: Map.put(error, :source, %{pointer: value})

lib/jsonapi/plugs/format_required.ex

@@ -12,6 +12,57 @@ defmodule JSONAPI.FormatRequired do
 
   def call(%{method: method} = conn, _opts) when method in ~w[DELETE GET HEAD], do: conn
 
+  def call(
+        %{method: method, params: %{"data" => %{"type" => _, "relationships" => relationships}}} =
+          conn,
+        _
+      )
+      when method in ~w[POST PATCH] and not is_map(relationships) do
+    send_error(conn, relationships_missing_object())
+  end
+
+  def call(
+        %{
+          method: method,
+          params: %{"data" => %{"type" => _, "relationships" => relationships}}
+        } = conn,
+        _
+      )
+      when method in ~w[POST PATCH] and is_map(relationships) do
+    errors =
+      Enum.reduce(relationships, [], fn
+        {_relationship_name, %{"data" => %{"type" => _type, "id" => _}}}, acc ->
+          acc
+
+        {relationship_name, %{"data" => %{"type" => _type}}}, acc ->
+          error = missing_relationship_data_id_param_error(relationship_name)
+          [error | acc]
+
+        {relationship_name, %{"data" => %{"id" => _type}}}, acc ->
+          error = missing_relationship_data_type_param_error(relationship_name)
+          [error | acc]
+
+        {relationship_name, %{"data" => %{}}}, acc ->
+          id_error = missing_relationship_data_id_param_error(relationship_name)
+          type_error = missing_relationship_data_type_param_error(relationship_name)
+          [id_error | [type_error | acc]]
+
+        {_relationship_name, %{"data" => _}}, acc ->
+          # Allow things other than resource identifier objects per https://jsonapi.org/format/#document-resource-object-linkage
+          acc
+
+        {relationship_name, _}, acc ->
+          error = missing_relationship_data_param_error(relationship_name)
+          [error | acc]
+      end)
+
+    if Enum.empty?(errors) do
+      conn
+    else
+      send_error(conn, serialize_errors(errors))
+    end
+  end
+
   def call(%{method: "POST", params: %{"data" => %{"type" => _}}} = conn, _), do: conn
 
   def call(%{method: method, params: %{"data" => [%{"type" => _} | _]}} = conn, _)