Add lazy eval

lib/batch_loader.rb

@@ -8,8 +8,8 @@
 require_relative "./batch_loader/graphql"
 
 class BatchLoader
-  IMPLEMENTED_INSTANCE_METHODS = %i[object_id __id__ __send__ singleton_method_added __sync respond_to? batch inspect].freeze
-  REPLACABLE_INSTANCE_METHODS = %i[batch inspect].freeze
+  IMPLEMENTED_INSTANCE_METHODS = %i[object_id __id__ __send__ singleton_method_added __sync respond_to? batch inspect lazy_eval __accepting_lazy_chain?].freeze
+  REPLACABLE_INSTANCE_METHODS = %i[batch inspect lazy_eval].freeze
   LEFT_INSTANCE_METHODS = (IMPLEMENTED_INSTANCE_METHODS - REPLACABLE_INSTANCE_METHODS).freeze
 
   NoBatchError = Class.new(StandardError)
@@ -37,6 +37,15 @@ def batch(default_value: nil, cache: true, replace_methods: nil, key: nil, &batc
     self
   end
 
+  def lazy_eval
+    @accepting_lazy_chain = true
+    @lazy_chain = []
+
+    __singleton_class.class_eval { undef_method(:lazy_eval) }
+
+    self
+  end
+
   def respond_to?(method_name, include_private = false)
     return true if LEFT_INSTANCE_METHODS.include?(method_name)
 
@@ -49,9 +58,13 @@ def inspect
 
   def __sync
     return @loaded_value if @synced
+    @accepting_lazy_chain = false
 
     __ensure_batched
     @loaded_value = __executor_proxy.loaded_value(item: @item)
+    (@lazy_chain || []).each do |method_name, args, kwargs, block|
+      @loaded_value = @loaded_value.public_send(method_name, *args, **kwargs, &block)
+    end
 
     if @cache
       @synced = true
@@ -62,6 +75,10 @@ def __sync
     @loaded_value
   end
 
+  def __accepting_lazy_chain?
+    @accepting_lazy_chain
+  end
+
   private
 
   def __loaded_value
@@ -70,7 +87,16 @@ def __loaded_value
   end
 
   def method_missing(method_name, *args, **kwargs, &block)
-    __sync!.public_send(method_name, *args, **kwargs, &block)
+    return __sync!.public_send(method_name, *args, **kwargs, &block) if !__accepting_lazy_chain?
+
+    return __sync! if method_name == :force
+
+    if method_name == :eager
+      @accepting_lazy_chain = false
+    else
+      @lazy_chain << [method_name, args, kwargs, block]
+    end
+    self
   end
 
   def __sync!

lib/batch_loader/graphql.rb

@@ -68,8 +68,18 @@ def batch(**kwargs, &block)
       self
     end
 
+    def lazy_eval
+      @batch_loader.lazy_eval
+      self
+    end
+
     def sync
       @batch_loader.__sync
     end
+
+    def method_missing(method_name, *args, **kwargs, &block)
+      super if !@batch_loader.__accepting_lazy_chain?
+      @batch_loader.public_send(method_name, *args, **kwargs, &block)
+    end
   end
 end

spec/batch_loader_spec.rb

@@ -220,7 +220,7 @@
 
       expect(batch_loader.inspect).to match(/#<BatchLoader:0x\w+>/)
       expect(batch_loader.to_s).to match(/#<User:0x\w+>/)
-      expect(batch_loader.inspect).to match(/#<User:0x\w+ @id=1>/)
+      expect(batch_loader.inspect).to match(/#<User:0x\w+ @id=1, @name=nil>/)
     end
   end
 
@@ -321,4 +321,26 @@
       expect { result.to_s }.to raise_error("Oops")
     end
   end
+
+  describe "#lazy_eval" do
+    it 'allows modifying the end result without adding more loaders' do
+      user1 = User.save(id: 1, name: "John")
+      user2 = User.save(id: 2, name: "Jane")
+      post1 = Post.new(user_id: user1.id)
+      post2 = Post.new(user_id: user2.id)
+      result = { user1: post1.user_lazy.lazy_eval.name.eager, user2: post2.user_lazy.lazy_eval.id.eager }
+
+      expect(User).to receive(:where).with(id: [1, 2]).once.and_call_original
+
+      expect(result).to eq(user1: "John", user2: 2)
+    end
+
+    it 'delegates the second then call to the loaded value' do
+      user = User.save(id: 1)
+      post = Post.new(user_id: user.id)
+
+      user_lazy_instance = post.user_lazy.lazy_eval
+      expect(user_lazy_instance.lazy_eval.eager).to eq("Lazy Eval from User")
+    end
+  end
 end

spec/fixtures/graphql_schema.rb

@@ -4,6 +4,8 @@ class UserType < GraphQL::Schema::Object
 
 class PostType < GraphQL::Schema::Object
   field :user, UserType, null: false
+  field :user_id, String, null: false
+  field :user_name, String, null: false
   field :user_old, UserType, null: false
 
   def user
@@ -12,6 +14,14 @@ def user
     end
   end
 
+  def user_id
+    user.lazy_eval.id
+  end
+
+  def user_name
+    user.lazy_eval.name
+  end
+
   def user_old
     BatchLoader.for(object.user_id).batch(default_value: nil) do |user_ids, loader|
       User.where(id: user_ids).each { |user| loader.call(user.id, user) }

spec/fixtures/models.rb

@@ -37,9 +37,9 @@ def user_lazy(**opts)
 
 class User
   class << self
-    def save(id:)
+    def save(id:, name: nil)
       ensure_init_store
-      @store[self][id] = new(id: id)
+      @store[self][id] = new(id: id, name: name)
     end
 
     def where(id:)
@@ -59,16 +59,21 @@ def ensure_init_store
     end
   end
 
-  attr_reader :id
+  attr_reader :id, :name
 
-  def initialize(id:)
+  def initialize(id:, name: nil)
     @id = id
+    @name = name
   end
 
   def batch
     "Batch from User"
   end
 
+  def lazy_eval
+    "Lazy Eval from User"
+  end
+
   def hash
     [User, id].hash
   end

spec/graphql_spec.rb

@@ -17,14 +17,16 @@
   end
 
   def test(schema)
-    user1 = User.save(id: "1")
-    user2 = User.save(id: "2")
+    user1 = User.save(id: "1", name: "John")
+    user2 = User.save(id: "2", name: "Jane")
     Post.save(user_id: user1.id)
     Post.save(user_id: user2.id)
     query = <<~QUERY
       {
         posts {
           user { id }
+          userName
+          userId
           userOld { id }
         }
       }
@@ -36,8 +38,8 @@ def test(schema)
 
     expect(result['data']).to eq({
       'posts' => [
-        {'user' => {'id' => "1"}, 'userOld' => {'id' => "1"}},
-        {'user' => {'id' => "2"}, 'userOld' => {'id' => "2"}}
+        {'user' => {'id' => "1"}, 'userOld' => {'id' => "1"}, 'userId' => "1", 'userName' => "John"},
+        {'user' => {'id' => "2"}, 'userOld' => {'id' => "2"}, 'userId' => "2", 'userName' => "Jane"}
       ]
     })
   end

spec/spec_helper.rb

@@ -1,4 +1,5 @@
 require "bundler/setup"
+require 'pry'
 
 if ENV['CI']
   require 'coveralls'