Dataloader support (#130)

Author: DmitryTsepelev

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## master
 
+- [PR#130](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/pull/130) Dataloader support ([@DmitryTsepelev][])
 - [PR#125](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/pull/125) Introduce cache lookup instrumentation hook ([@danielhartnell][])
 
 ## 1.20.5 (2024-11-02)

README.md

@@ -381,6 +381,34 @@ class QueryType < BaseObject
 end
 ```
 
+## Dataloader
+
+If you are using [Dataloader](https://graphql-ruby.org/dataloader/overview.html), you will need to let the gem know using `dataloader: true`:
+
+```ruby
+class PostType < BaseObject
+  field :author, User, null: false
+
+  def author
+    cache_fragment(dataloader: true) do
+      dataloader.with(AuthorDataloaderSource).load(object.id)
+    end
+  end
+end
+
+# or
+
+class PostType < BaseObject
+  field :author, User, null: false, cache_fragment: {dataloader: true}
+
+  def author
+    dataloader.with(AuthorDataloaderSource).load(object.id)
+  end
+end
+```
+
+The problem is that I didn't find a way to detect that dataloader (and, therefore, Fiber) is used, and the block is forced to resolve, causing the N+1 inside the Dataloader Source class.
+
 ## How to use `#cache_fragment` in extensions (and other places where context is not available)
 
 If you want to call `#cache_fragment` from places other that fields or resolvers, you'll need to pass `context` explicitly and turn on `raw_value` support. For instance, let's take a look at this extension:

lib/graphql/fragment_cache/fragment.rb

@@ -16,12 +16,10 @@ def read_multi(fragments)
             return fragments.map { |f| [f, f.read] }.to_h
           end
 
-          fragments_to_cache_keys = fragments
-            .map { |f| [f, f.cache_key] }.to_h
+          fragments_to_cache_keys = fragments.map { |f| [f, f.cache_key] }.to_h
 
           # Filter out all the cache_keys for fragments with renew_cache: true in their context
-          cache_keys = fragments_to_cache_keys
-            .reject { |k, _v| k.context[:renew_cache] == true }.values
+          cache_keys = fragments_to_cache_keys.reject { |k, _v| k.context[:renew_cache] == true }.values
 
           # If there are cache_keys look up values with read_multi otherwise return an empty hash
           cache_keys_to_values = if cache_keys.empty?
@@ -46,8 +44,7 @@ def read_multi(fragments)
           end
 
           # Fragmenst without values or with renew_cache: true in their context will have nil values like the read method
-          fragments_to_cache_keys
-            .map { |fragment, cache_key| [fragment, cache_keys_to_values[cache_key]] }.to_h
+          fragments_to_cache_keys.map { |fragment, cache_key| [fragment, cache_keys_to_values[cache_key]] }.to_h
         end
       end
 

lib/graphql/fragment_cache/schema/lazy_cache_resolver.rb

@@ -16,6 +16,8 @@ def initialize(fragment, query_ctx, object_to_cache, &block)
           @block = block
 
           @lazy_state[:pending_fragments] << @fragment
+
+          ensure_dataloader_resulution! if @fragment.options[:dataloader]
         end
 
         def resolve
@@ -35,6 +37,15 @@ def resolve
             @query_ctx.fragments << @fragment
           end
         end
+
+        private
+
+        def ensure_dataloader_resulution!
+          return if FragmentCache.cache_store.exist?(@fragment.cache_key)
+
+          @object_to_cache = @block.call
+          @block = nil
+        end
       end
     end
   end

spec/graphql/fragment_cache/object_helpers_spec.rb

@@ -777,6 +777,62 @@ def post(id:, expires_in: nil)
     end
   end
 
+  describe "caching fields with dataloader" do
+    let(:query) do
+      <<~GQL
+        query GetPosts {
+          posts {
+            id
+            dataloaderCachedAuthor {
+              name
+            }
+          }
+        }
+      GQL
+    end
+
+    let(:schema) do
+      build_schema do
+        use GraphQL::Dataloader
+        query(Types::Query)
+      end
+    end
+
+    let(:user1) { User.new(id: 1, name: "User #1") }
+    let(:user2) { User.new(id: 2, name: "User #2") }
+
+    let!(:post1) { Post.create(id: 1, title: "object test 1", author: user1) }
+    let!(:post2) { Post.create(id: 2, title: "object test 2", author: user2) }
+
+    let(:memory_store) { GraphQL::FragmentCache::MemoryStore.new }
+
+    before do
+      allow(User).to receive(:find_by_post_ids).and_call_original
+
+      # warmup cache
+      execute_query
+
+      # make objects dirty
+      user1.name = "User #1 new"
+      user2.name = "User #2 new"
+    end
+
+    it "returns cached results" do
+      expect(execute_query.dig("data", "posts")).to eq([
+        {
+          "id" => "1",
+          "dataloaderCachedAuthor" => {"name" => "User #1"}
+        },
+        {
+          "id" => "2",
+          "dataloaderCachedAuthor" => {"name" => "User #2"}
+        }
+      ])
+
+      expect(User).to have_received(:find_by_post_ids).with([post1.id, post2.id]).once
+    end
+  end
+
   describe "conditional caching" do
     let(:schema) do
       field_resolver = resolver

spec/graphql/fragment_cache/schema/lazy_cache_resolver_spec.rb

@@ -6,21 +6,27 @@
   describe "#initialize" do
     context "lazy cache resolver state management" do
       let(:state_key) { :lazy_cache_resolver_statez }
+      let(:gql_context) { instance_double "Context" }
+      let(:fragment) { GraphQL::FragmentCache::Fragment.new(gql_context) }
+
+      before do
+        allow(gql_context).to receive(:namespace).and_return({})
+      end
 
       it "adds lazy state property to the query context" do
         context = {}
 
         expect(context).not_to have_key(state_key)
 
-        GraphQL::FragmentCache::Schema::LazyCacheResolver.new(nil, context, {})
+        GraphQL::FragmentCache::Schema::LazyCacheResolver.new(fragment, context, {})
 
         expect(context).to have_key(state_key)
       end
 
       it "has :pending_fragments Set in state" do
         context = {}
 
-        GraphQL::FragmentCache::Schema::LazyCacheResolver.new({}, context, {})
+        GraphQL::FragmentCache::Schema::LazyCacheResolver.new(fragment, context, {})
 
         expect(context[state_key]).to have_key(:pending_fragments)
         expect(context[state_key][:pending_fragments]).to be_instance_of(Set)
@@ -29,7 +35,7 @@
       it "has :resolved_fragments Hash in state" do
         context = {}
 
-        GraphQL::FragmentCache::Schema::LazyCacheResolver.new({}, context, {})
+        GraphQL::FragmentCache::Schema::LazyCacheResolver.new(fragment, context, {})
 
         expect(context[state_key]).to have_key(:resolved_fragments)
         expect(context[state_key][:resolved_fragments]).to be_instance_of(Hash)
@@ -39,7 +45,7 @@
         context = {}
         fragments = []
 
-        3.times { fragments.push(Object.new) }
+        3.times { fragments.push(GraphQL::FragmentCache::Fragment.new(gql_context)) }
 
         fragments.each do |f|
           GraphQL::FragmentCache::Schema::LazyCacheResolver.new(f, context, {})
@@ -51,10 +57,4 @@
       end
     end
   end
-
-  it "has :resolve method" do
-    lazy_cache_resolver = GraphQL::FragmentCache::Schema::LazyCacheResolver.new({}, {}, {})
-
-    expect(lazy_cache_resolver).to respond_to(:resolve)
-  end
 end

spec/support/models/user.rb

@@ -4,6 +4,12 @@ class User
   attr_reader :id
   attr_accessor :name
 
+  class << self
+    def find_by_post_ids(post_ids)
+      post_ids.map { |id| Post.find(id).author }
+    end
+  end
+
   def initialize(id:, name:)
     @id = id
     @name = name

spec/support/test_schema.rb

@@ -7,6 +7,12 @@ def perform(posts)
   end
 end
 
+class AuthorDataloaderSource < GraphQL::Dataloader::Source
+  def fetch(post_ids)
+    User.find_by_post_ids(post_ids)
+  end
+end
+
 module Types
   class Base < GraphQL::Schema::Object
     include GraphQL::FragmentCache::Object
@@ -41,6 +47,7 @@ class Post < Base
     field :cached_author, User, null: false
     field :batched_cached_author, User, null: false
     field :cached_author_inside_batch, User, null: false
+    field :dataloader_cached_author, User, null: false
 
     field :meta, String, null: true
 
@@ -60,6 +67,12 @@ def cached_author_inside_batch
         cache_fragment(author, context: context)
       end
     end
+
+    def dataloader_cached_author
+      cache_fragment(dataloader: true) do
+        dataloader.with(AuthorDataloaderSource).load(object.id)
+      end
+    end
   end
 
   class PostInput < GraphQL::Schema::InputObject