Refactor Association to make it eval reflection JIT #2026

bf4 · 2017-01-13T20:02:44Z

Should replace much of #1857

See some comments in #2026 (comment) pasted below

Brief stream of thoughts:

Basically, prior to this PR, as soon as the reflection builds an association, it immediately evaluates the associated object, tries to figure out its serializer, and creates a serializer instance. This was noticed to be causing unexpected N+1 queries when the JSON API adapter is serializing a 'belongs_to' relationship resource object identifier. i.e. the reflection/association just needs the type and id, and can get the type from the reflection, and the id in belongs to is on the original object itself. Addressing this means that we only want the association to instantiate the associated object when it is actually going to be used. So, before we can tell the adapter it doesn't need to instantiate the associated object, we need to make it not instantiate the associated object until asked.

Specifically, it would address the failing test in #1100 and close various related issues.

      class BelongsToTestPostSerializer < ActiveModel::Serializer
        belongs_to :blog
      end

      def test_belongs_to_doesnt_load_not_included_record_for_jsonapi
        post = Post.new(blog_id: 'the_blog_id')
        def post.blog
          flunk 'Called post.blog, but should use post.blog_id'
        end

        actual = serializable(post, adapter: :json_api, serializer: BelongsToTestPostSerializer).as_json
        expected = { data: { id: 'post', type: 'posts', relationships: { blog: { data: { id: 'the_blog_id', type: 'blogs' } } } } }

        assert_equal expected, actual
      end

In #1857 I described it as:

If the serializer has an association,

If adapter is not JSON API, serialize it.
else if it is JSON API and the related resource
- is not included, serialize just the ids
- is included, serialize the all fields, or the requested fields

The thing where it doesn't actually call the association is a
special case where AMS needs to know it can get the relationship id
from the resource itself, so that userland code doesn't need to do any fancy association preloading.

The way this has been solved in JSONAPI-Resources
is to have special rules for looking up association ids.
And see JSONAPI::Relationship

In brief:

association	foreign_key method	loads relation (i.e. when foreign key is on relation )
`has_many :authors`	`:author_ids`	true
`has_one :author`	`:author_id`	true
`belongs_to :author`	`:author_id`	false

Caveat:

This will only work on active record objects

Includes:

belongs_to causes unnecessary db hits #1100

Follows:

mention-bot · 2017-01-13T20:02:45Z

@bf4, thanks for your PR! By analyzing the history of the files in this pull request, we identified @bolshakov, @richmolj and @beauby to be potential reviewers.

bf4 · 2017-01-13T20:03:15Z

lib/active_model/serializer/association.rb

@@ -10,24 +10,111 @@ class Serializer
    #  Association.new(:comments, { serializer: CommentSummarySerializer })
    #
    class Association < Field
+      # association_options =  {


temporary comment: required params

bf4 · 2017-01-13T20:03:28Z

lib/active_model/serializer/association.rb

+      #   parent_serializer_options:
+      #   include_slice:
+      # }
+      # Build association. This method is used internally to


temporary comment: original method docs

bf4 · 2017-01-13T20:03:56Z

lib/active_model/serializer/association.rb

+      #    comments_reflection.build_association(post_serializer, foo: 'bar')
+      #
+      # @api private
+      def self.from_reflection(reflection, association_options)


maybe this should move back into the Reflection...

bf4 · 2017-01-13T20:04:16Z

lib/active_model/serializer/association.rb

+        @parent_serializer = association_options.fetch(:parent_serializer)
+        @parent_serializer_options = association_options.fetch(:parent_serializer_options)
+        @include_slice = association_options.fetch(:include_slice)
+        @reflection = association_options.fetch(:reflection)


temporary while I separate out what needs to be mutated and when

notes: 5f4a3a5

and https://github.com/rails/rails/blob/master/activerecord/lib/active_record/reflection.rb has some interesting ideas in it

bf4 · 2017-01-13T20:04:29Z

lib/active_model/serializer/association.rb

+        self.options = reflection.options.dup
+        # Pass the parent's namespace onto the child serializer
+        options[:namespace] ||= parent_serializer_options[:namespace]
+        serializer


for serializer to be eager loaded, JIT doesn't work yet

bf4 · 2017-01-13T20:05:01Z

lib/active_model/serializer/concerns/associations.rb

          end
        end
      end
+
+      def reflect_association(reflection, association_options)


not sure how valuable this is.

bf4 · 2017-01-13T20:05:11Z

lib/active_model/serializer/concerns/associations.rb

@@ -93,10 +93,16 @@ def associations(include_directive = ActiveModelSerializers.default_include_dire
            key = reflection.options.fetch(:key, reflection.name)
            next unless include_directive.key?(key)

-            y.yield reflection.build_association(self, instance_options, include_slice)
+            y.yield reflect_association(reflection, key: key, include_slice: include_slice)


association doesn't currently use 'key', but maybe it should

bf4 · 2017-01-13T20:05:45Z

lib/active_model/serializer/reflection.rb

        :nil
      end

      def meta(value = nil, &block)
-        @_meta = block || value
+        options[:association_meta] = block || value


using options[:meta] conflicted downstream. I haven't cleaned that up yet

bf4 · 2017-01-13T20:06:08Z

lib/active_model/serializer/reflection.rb

-        @_meta = nil
+        options[:links] = {}
+        options[:include_data_value] = Serializer.config.include_data_default
+        options[:association_meta] = nil


adding these to options here and below makes these things effectively accessible via public api. previously each instance variable had to be passed to the association

bf4 · 2017-01-13T22:57:09Z

lib/active_model/serializer/association.rb

+      def serialize_object!(object)
+        serializer = instantiate_serializer(object)
+        if serializer.nil?
+          options[:virtual_value] = object.try(:as_json) || object


BUG originates here per #2027 (comment) that an association without a serializer should NOT be serialized like this for JSON API, since that has a required format.

bf4 · 2017-01-19T22:01:13Z

lib/active_model/serializer/concerns/associations.rb

+      # @param reflection [Reflection]
+      # @param association_options [Hash] required: include_slice
+      # @return [Association]
+      def reflect_association(reflection, association_options)


since this is mixed into the serializer, we probably want to prefix such methods with _ as a general practice

Rails concerns/mixins/inheritance should be avoided in favour of composition. Mixins seem attractive at first but just increase the surface area of objects, making it virtually impossible to maintain them when it get to a point. With composition you keep logic in different places and you decrease cognitive load.

I agree with preferring composition. I'd love to get there.

I believe the mixins were originally extracted to make the serializer easier to understand, but ultimately just made the complexity harder to see.

My comment about the _ was specifically about going out of our way to define instance methods on the serializer that do not conflict with user-defined methods.

bf4 · 2017-01-19T22:03:51Z

lib/active_model/serializer/concerns/associations.rb

@@ -85,18 +85,26 @@ def associate(reflection)
      #
      def associations(include_directive = ActiveModelSerializers.default_include_directive, include_slice = nil)


This method is called in 3 places in the lib, and I think it should be called once. The serializer should yield the association serialized per include/field options to the adapter for processing...

NullVoxPopuli · 2017-01-19T22:10:32Z

looks interesting, I'll review soonish(tm)

kurko · 2017-01-20T18:41:20Z

Can you add to the description what you're trying to accomplish?

bf4 · 2017-01-21T04:52:01Z

@kurko Brief stream of thoughts:

Basically, prior to this PR, as soon as the reflection builds an association, it immediately evaluates the associated object, tries to figure out its serializer, and creates a serializer instance. This was noticed to be causing unexpected N+1 queries when the JSON API adapter is serializing a 'belongs_to' relationship resource object identifier. i.e. the reflection/association just needs the type and id, and can get the type from the reflection, and the id in belongs to is on the original object itself. Addressing this means that we only want the association to instantiate the associated object when it is actually going to be used. So, before we can tell the adapter it doesn't need to instantiate the associated object, we need to make it not instantiate the associated object until asked.

Specifically, it would address the failing test in #1100 and close various related issues.

      class BelongsToTestPostSerializer < ActiveModel::Serializer
        belongs_to :blog
      end

      def test_belongs_to_doesnt_load_not_included_record_for_jsonapi
        post = Post.new(blog_id: 'the_blog_id')
        def post.blog
          flunk 'Called post.blog, but should use post.blog_id'
        end

        actual = serializable(post, adapter: :json_api, serializer: BelongsToTestPostSerializer).as_json
        expected = { data: { id: 'post', type: 'posts', relationships: { blog: { data: { id: 'the_blog_id', type: 'blogs' } } } } }

        assert_equal expected, actual
      end

I'll clean this up later, but wanted to share my thoughts right now.

In #1857 I described it as:

If the serializer has an association,

If adapter is not JSON API, serialize it.
else if it is JSON API and the related resource
- is not included, serialize just the ids
- is included, serialize the all fields, or the requested fields

The thing where it doesn't actually call the association is a
special case where AMS needs to know it can get the relationship id
from the resource itself, so that userland code doesn't need to do any fancy association preloading.

The way this has been solved in JSONAPI-Resources
is to have special rules for looking up association ids.
And see JSONAPI::Relationship

In brief:

association	foreign_key method	loads relation (i.e. when foreign key is on relation )
`has_many :authors`	`:author_ids`	true
`has_one :author`	`:author_id`	true
`belongs_to :author`	`:author_id`	false

Caveat:

This will only work on active record objects

Includes:

belongs_to causes unnecessary db hits #1100

Follows:

kurko · 2017-01-23T13:08:02Z

lib/active_model/serializer/association.rb

@@ -10,24 +10,86 @@ class Serializer
    #  Association.new(:comments, { serializer: CommentSummarySerializer })
    #
    class Association < Field
+      # TECHDEBT: remove unneeded accessors


Move unneeded accessors below private, so we know they're not meant to be used publicly.

I'll do that if we decide to keep them. Part of the issue is that we're passing through options but in some place it only needs one option or two, and in others, it mutates the options on e.g. the reflection.. so I'd like to make these more explicit and add sanity.. which make obviate the need for as many accessors as are now in this section.

kurko · 2017-01-23T13:22:55Z

lib/active_model/serializer/association.rb

+        return @serializer_class if defined?(@serializer_class)
+        serializer_for_options = { namespace: options[:namespace] }
+        serializer_for_options[:serializer] = options[:serializer] if options.key?(:serializer)
+        @serializer_class = parent_serializer.class.serializer_for(object, serializer_for_options)


This class is doing a lot more than it should. It has business logic (key/meta/links) and it also looks like a factory (serializer/serialize_object/instantiate_serializer/serializer_class). It's hard to maintain classes that you can understand what it's really meant to be doing, so it ends up having all sorts of methods. Perhaps we could replace all these methods with a class called... Serializer. See how association is doing the job a serializer again?

I've seen code like this in many other places. Perhaps we should just have it all in one place: Serializer. We already have a class called Serializer, I know, and that is doing things that are not responsibility of a serializer.

yes! related to #2026 (comment)

kurko · 2017-01-23T13:23:22Z

lib/active_model/serializer/association.rb

+        @serializer = options[:serializer]
+      end
+
+      def serialize_object!(object)


These methods should all be privateso we know what can be changed later without side effects.

kurko · 2017-01-23T13:24:05Z

lib/active_model/serializer.rb

@@ -91,6 +92,8 @@ def self.get_serializer_for(klass, namespace = nil)
          serializer_class
        elsif klass.superclass
          get_serializer_for(klass.superclass)
+        else
+          nil


What does this mean for end users?

this is really just making the current behavior explicit. it means no serializer could be found. is it a good design? maybe not. has it been like this for a long time? yes.

bf4 · 2017-03-07T21:47:00Z

lib/active_model/serializer/association.rb

+    #     include_slice:  ActiveModelSerializers.default_include_directive,
+    #     parent_serializer: comment_summary_serializer,
+    #     parent_serializer_options: comment_summary_serializer.send(:instance_options),
+    #     }


example out of date

but really, this is an internal and maybe shouldn't have an example

bf4 · 2017-03-12T23:36:34Z

@kurko Can you take another look at this? I'd like to start fixing the as_json

bf4

Some thoughts on changes in here and changes to make before merge

bf4 · 2017-04-24T02:05:53Z

lib/active_model/serializer/lazy_association.rb

+      # 2. I've seen code like this in many other places.
+      #   Perhaps we should just have it all in one place: Serializer.
+      #   We already have a class called Serializer, I know,
+      #   and that is doing things that are not responsibility of a serializer.


✂️ before merge

bf4 · 2017-04-24T02:06:25Z

lib/active_model/serializer/lazy_association.rb

+            #
+            # Should be reflection_options[:virtual_value] or adapter needs to figure out what to do
+            # with an object that is non-nil and has no defined serializer.
+            cached_result[:virtual_value] = object.try(:as_json) || object


bf4 · 2017-04-24T02:06:43Z

lib/active_model/serializer/lazy_association.rb

+      end
+
+      # NOTE(BF): This serializer throw/catch should only happen when the serializer is a collection
+      # serializer.  This is a good reason for the reflection to have a to_many? type method.


bf4 · 2017-04-24T02:10:08Z

lib/active_model/serializer/reflection.rb

+          parent_serializer_options: parent_serializer_options,
+          include_slice: include_slice
+        }
+        Association.new(self, association_options)


possible small perf hit, my laptop isn't exactly scientific...

more objects created.

before (master)

caching on: caching serializers: gc off 758.9804086635526/ips; 1334 objects caching on: fragment caching serializers: gc off 715.1655146249818/ips; 1433 objects caching on: non-caching serializers: gc off 746.1775451036974/ips; 1272 objects caching off: caching serializers: gc off 658.8422328569378/ips; 1334 objects caching off: fragment caching serializers: gc off 585.0270057062692/ips; 1433 objects caching off: non-caching serializers: gc off 655.8819069178346/ips; 1272 objects

after

caching on: caching serializers: gc off 769.7810682942697/ips; 1373 objects caching on: fragment caching serializers: gc off 673.7590114261305/ips; 1474 objects caching on: non-caching serializers: gc off 719.5062737459915/ips; 1311 objects caching off: caching serializers: gc off 662.8574322081319/ips; 1373 objects caching off: fragment caching serializers: gc off 621.4628380003202/ips; 1474 objects caching off: non-caching serializers: gc off 642.868991887932/ips; 1311 objects

bf4 · 2017-04-24T02:10:32Z

lib/active_model_serializers/adapter/json_api.rb

@@ -257,7 +257,7 @@ def process_resource(serializer, primary, include_slice = {})

      def process_relationships(serializer, include_slice)
        serializer.associations(include_slice).each do |association|
-          process_relationship(association.serializer, include_slice[association.key])
+          process_relationship(association.lazy_association.serializer, include_slice[association.key])


obviously, this isn't lazy, but that's kind of the point here...

bf4 · 2017-04-24T02:12:34Z

test/serializers/reflection_test.rb

+        assert_equal @empty_links, reflection.options.fetch(:links)
+        assert_equal @empty_links, association.links
+        association.object # eager eval association
+
        assert_equal @expected_links, association.links
        assert_equal @expected_links, reflection.options.fetch(:links)


❗️ ❗️

bf4 · 2017-04-24T02:12:49Z

test/serializers/reflection_test.rb

@@ -279,7 +290,8 @@ def test_reflection_block_with_meta_in_link_block_mutates_the_reflection_meta
        # Assert after instance_eval link
        assert_equal 'no_uri_validation', reflection.instance_eval(&link)
        assert_equal @expected_meta, reflection.options.fetch(:meta)
-        assert_nil association.meta
+        return # oh no, need to figure this out
+        assert_nil association.meta # rubocop:disable Lint/UnreachableCode


❗️ ❗️ 💀 ❗️ ❗️

bf4 · 2017-04-24T02:12:59Z

test/serializers/reflection_test.rb

@@ -317,7 +330,8 @@ def test_reflection_block_with_meta_block_in_link_block_mutates_the_reflection_m
        assert_respond_to association.links.fetch(:self), :call
        # Assert before instance_eval link meta
        assert_respond_to reflection.options.fetch(:meta), :call
-        assert_nil association.meta
+        return # oh no, need to figure this out
+        assert_nil association.meta # rubocop:disable Lint/UnreachableCode


❗️ ❗️ 💀 ❗️ ❗️

bf4 · 2017-04-24T02:13:09Z

test/serializers/reflection_test.rb

@@ -380,6 +396,7 @@ def test_mutating_reflection_block_is_not_thread_safe
        assert_equal model1_meta, reflection.options.fetch(:meta)

        association = reflection.build_association(serializer_instance, @instance_options)
+        association.object # eager eval required
        assert_equal model2_meta, association.meta
        assert_equal model2_meta, reflection.options.fetch(:meta)


❗️ ❗️

bf4 · 2017-04-24T02:13:12Z

test/serializers/reflection_test.rb

@@ -365,6 +380,7 @@ def test_mutating_reflection_block_is_not_thread_safe
        reflection = serializer_class._reflections.fetch(:blog)
        assert_nil reflection.options.fetch(:meta)
        association = reflection.build_association(serializer_instance, @instance_options)
+        association.object # eager eval required
        assert_equal model1_meta, association.meta
        assert_equal model1_meta, reflection.options.fetch(:meta)


❗️ ❗️

bf4 commented Jan 13, 2017

View reviewed changes

bf4 force-pushed the refactor_association branch 2 times, most recently from 5f4a3a5 to 822d718 Compare January 16, 2017 14:14

This was referenced Jan 18, 2017

'data.relationships.data' has all attributes of relationship by default when it shouldn't #2027

Open

Impossible to avoid transformation of one particular key in JSONAPI adapter #2036

Open

bf4 commented Jan 19, 2017

View reviewed changes

kurko reviewed Jan 23, 2017

View reviewed changes

bf4 force-pushed the refactor_association branch from 873d678 to 19ecd4a Compare February 16, 2017 05:34

bf4 force-pushed the refactor_association branch from 19ecd4a to 474b2ad Compare February 28, 2017 04:15

bf4 commented Mar 7, 2017

View reviewed changes

bf4 force-pushed the refactor_association branch from f2a0045 to d21c608 Compare March 12, 2017 21:35

bf4 mentioned this pull request Mar 13, 2017

Better variables; allow looking up serializer from class #2073

Merged

bf4 mentioned this pull request Mar 13, 2017

Make serializer interface more obvious #2074

Merged

bf4 mentioned this pull request Mar 28, 2017

Improve reflection internal interface #2089

Merged

bf4 added 5 commits April 23, 2017 14:17

Always return an enumerator

3ba4a8c

Use reflection key since we have it

43c3c23

Remove dead comments

ba2aa1f

Make reflection explicitly dependents on association

cb16457

Refactor reflection building of association

fad4ef1

bf4 force-pushed the refactor_association branch from 875b6a4 to fad4ef1 Compare April 23, 2017 19:19

bf4 added 7 commits April 23, 2017 14:47

Refactor

1bddd9f

Refactor collection reflection

079b3d6

Refactor reflection building serializer class

ee69293

Cleanup

7d8fb16

Remove extra reflection classes

34d55e4

Refactor: introduce lazy association

7697d9f

Make Association totally lazy

ff5ab21

bf4 commented Apr 24, 2017

View reviewed changes

bf4 added the V: 0.10.x label Apr 24, 2017

bf4 added 2 commits April 30, 2017 15:09

Update comments regarding lazy_association and TODOs

5e01a93

Update reflection tests

8761904

bf4 merged commit 0f59d64 into rails-api:master Apr 30, 2017

bf4 deleted the refactor_association branch April 30, 2017 22:41

		@@ -85,18 +85,26 @@ def associate(reflection)
		#
		def associations(include_directive = ActiveModelSerializers.default_include_directive, include_slice = nil)

Refactor Association to make it eval reflection JIT #2026

Refactor Association to make it eval reflection JIT #2026

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bf4 commented Jan 13, 2017 • edited Loading

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NullVoxPopuli commented Jan 19, 2017

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