Associations: Support :primary_key and :foreign_key

The problem
---

Some `has_many` and `has_one` associations provided by APIs are "joined"
by properties other than their `id` (or an overridden `primary_key`).

The proposal
---

By default, continue to infer the `:foreign_key` as
`self.class.element_name + "_id"` and its `:primary_key` from the value
of its primary key (returned by the `id` method).

When necessary, `has_many` declarations can declare `:primary_key` and
`:foreign_key` options in the same style as [Active Record's `has_many`
associations][has_many].

[has_many]: https://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many

Author: seanpdoyle

lib/active_resource/associations.rb

@@ -16,6 +16,13 @@ module Builder
   # [:class_name]
   #   Specify the class name of the association. This class name would
   #   be used for resolving the association class.
+  # [:foreign_key]
+  #   Specify the foreign key used for the association. By default, the key is
+  #   inferred from the associated `element_name` class method with an "_id"
+  #   suffix.
+  # [:primary_key]
+  #   Specify the primary key used for the association. By default, the key is
+  #   inferred from the `primary_key` class method.
   #
   # ==== Example for [:class_name] - option
   # GET /posts/123.json delivers following response body:
@@ -50,6 +57,13 @@ def has_many(name, options = {})
   # [:class_name]
   #   Specify the class name of the association. This class name would
   #   be used for resolving the association class.
+  # [:foreign_key]
+  #   Specify the foreign key used for the association. By default, the key is
+  #   inferred from the associated `element_name` class method with an "_id"
+  #   suffix.
+  # [:primary_key]
+  #   Specify the primary key used for the association. By default, the key is
+  #   inferred from the `primary_key` class method.
   #
   # ==== Example for [:class_name] - option
   # GET /posts/1.json delivers following response body:
@@ -141,14 +155,18 @@ def defines_belongs_to_finder_method(reflection)
   def defines_has_many_finder_method(reflection)
     method_name = reflection.name
     ivar_name = :"@#{method_name}"
+    options = reflection.options
 
     define_method(method_name) do
+      foreign_key = options.fetch(:foreign_key, "#{self.class.element_name}_id")
+      primary_key = send(options.fetch(:primary_key, self.class.primary_key))
+
       if instance_variable_defined?(ivar_name)
         instance_variable_get(ivar_name)
       elsif attributes.include?(method_name)
         read_attribute(method_name)
       elsif !new_record?
-        instance_variable_set(ivar_name, reflection.klass.where("#{self.class.element_name}_id": self.id))
+        instance_variable_set(ivar_name, reflection.klass.where(foreign_key => primary_key))
       else
         instance_variable_set(ivar_name, self.class.collection_parser.new)
       end
@@ -159,16 +177,20 @@ def defines_has_many_finder_method(reflection)
   def defines_has_one_finder_method(reflection)
     method_name = reflection.name
     ivar_name = :"@#{method_name}"
+    options = reflection.options
 
     define_method(method_name) do
+      foreign_key = options.fetch(:foreign_key, "#{self.class.element_name}_id")
+      primary_key = send(options.fetch(:primary_key, self.class.primary_key))
+
       if instance_variable_defined?(ivar_name)
         instance_variable_get(ivar_name)
       elsif attributes.include?(method_name)
         read_attribute(method_name)
       elsif reflection.klass.respond_to?(:singleton_name)
-        instance_variable_set(ivar_name, reflection.klass.find(params: { "#{self.class.element_name}_id": self.id }))
+        instance_variable_set(ivar_name, reflection.klass.find(params: { foreign_key => primary_key }))
       else
-        instance_variable_set(ivar_name, reflection.klass.find(:one, from: "/#{self.class.collection_name}/#{self.id}/#{method_name}#{self.class.format_extension}"))
+        instance_variable_set(ivar_name, reflection.klass.find(:one, from: "/#{self.class.collection_name}/#{primary_key}/#{method_name}#{self.class.format_extension}"))
       end
     end
   end

lib/active_resource/associations/builder/has_many.rb

@@ -2,6 +2,8 @@
 
 module ActiveResource::Associations::Builder
   class HasMany < Association
+    self.valid_options += [ :primary_key, :foreign_key ]
+
     self.macro = :has_many
 
     def build

lib/active_resource/associations/builder/has_one.rb

@@ -2,6 +2,8 @@
 
 module ActiveResource::Associations::Builder
   class HasOne < Association
+    self.valid_options += [ :primary_key, :foreign_key ]
+
     self.macro = :has_one
 
     def build

test/cases/association_test.rb

@@ -5,14 +5,19 @@
 require "fixtures/person"
 require "fixtures/beast"
 require "fixtures/customer"
+require "fixtures/weather"
 
 
 class AssociationTest < ActiveSupport::TestCase
   def setup
     @klass = ActiveResource::Associations::Builder::Association
     @reflection = ActiveResource::Reflection::AssociationReflection.new :belongs_to, :customer, {}
+    @previous_reflections, External::Person.reflections = External::Person.reflections, {}
   end
 
+  def teardown
+    External::Person.reflections = @previous_reflections
+  end
 
   def test_validations_for_instance
     object = @klass.new(Person, :customers, {})
@@ -48,6 +53,28 @@ def test_has_many
     assert_equal [ "Related" ], people.map(&:name)
   end
 
+  def test_has_many_with_primary_key
+    External::Person.has_many(:people, primary_key: :parent_id)
+
+    ActiveResource::HttpMock.respond_to.get "/people.json?person_id=1", {}, { people: [ { id: 2, name: "Related" } ] }.to_json
+    person = External::Person.new({ parent_id: 1 }, true)
+
+    people = person.people
+
+    assert_equal [ "Related" ], people.map(&:name)
+  end
+
+  def test_has_many_with_foreign_key
+    External::Person.has_many(:people, foreign_key: :parent_id)
+
+    ActiveResource::HttpMock.respond_to.get "/people.json?parent_id=1", {}, { people: [ { id: 2, name: "Related" } ] }.to_json
+    person = External::Person.new({ id: 1 }, true)
+
+    people = person.people
+
+    assert_equal [ "Related" ], people.map(&:name)
+  end
+
   def test_has_many_chain
     External::Person.send(:has_many, :people)
 
@@ -68,6 +95,62 @@ def test_has_many_on_new_record
   def test_has_one
     External::Person.send(:has_one, :customer)
     assert_equal 1, External::Person.reflections.select { |name, reflection| reflection.macro.eql?(:has_one) }.count
+
+    ActiveResource::HttpMock.respond_to.get "/people/1/customer.json", {}, { person: { id: 2, name: "Customer" } }.to_json
+    person = External::Person.new({ id: 1 }, true)
+
+    customer = person.customer
+
+    assert_equal "Customer", customer.name
+  end
+
+  def test_has_one_singleton
+    External::Person.send(:has_one, :weather)
+
+    ActiveResource::HttpMock.respond_to.get "/weather.json?person_id=1", {}, { weather: { id: 1, status: "Sunshine" } }.to_json
+    person = External::Person.new({ id: 1 }, true)
+
+    weather = person.weather
+
+    assert_equal "Sunshine", weather.status
+  end
+
+  def test_has_one_with_primary_key
+    External::Person.send(:has_one, :customer, primary_key: :customer_id)
+
+    ActiveResource::HttpMock.respond_to.get "/people/1/customer.json", {}, { person: { id: 2, name: "Customer" } }.to_json
+    person = External::Person.new({ customer_id: 1 }, true)
+
+    customer = person.customer
+
+    assert_equal "Customer", customer.name
+  end
+
+  def test_has_one_singleton_with_primary_key
+    External::Person.send(:has_one, :weather, primary_key: :person_id)
+
+    ActiveResource::HttpMock.respond_to.get "/weather.json?person_id=1", {}, { weather: { id: 1, status: "Sunshine" } }.to_json
+    person = External::Person.new({ person_id: 1 }, true)
+
+    weather = person.weather
+
+    assert_equal "Sunshine", weather.status
+  end
+
+  def test_has_one_singleton_with_foreign_key
+    previous_prefix = Weather.prefix
+    Weather.prefix = "/people/:owner_id/"
+
+    External::Person.send(:has_one, :weather, foreign_key: :owner_id)
+
+    ActiveResource::HttpMock.respond_to.get "/people/1/weather.json", {}, { weather: { id: 1, status: "Sunshine" } }.to_json
+    person = External::Person.new({ id: 1 }, true)
+
+    weather = person.weather
+
+    assert_equal "Sunshine", weather.status
+  ensure
+    Weather.prefix = previous_prefix
   end
 
   def test_belongs_to

test/cases/associations/builder/has_many_test.rb

@@ -25,4 +25,14 @@ def test_instance_build
     assert_equal :street_address, reflection.name
     assert_equal StreetAddress, reflection.klass
   end
+
+  def test_valid_options
+    assert @klass.build(Person, :street_address, class_name: "StreetAddress")
+    assert @klass.build(Person, :street_address, foreign_key: "person_id")
+    assert @klass.build(Person, :street_address, primary_key: "id")
+
+    assert_raise ArgumentError do
+      @klass.build(Person, :street_address, soo_invalid: true)
+    end
+  end
 end

test/cases/associations/builder/has_one_test.rb

@@ -25,4 +25,14 @@ def test_instance_build
     assert_equal :inventory, reflection.name
     assert_equal Inventory, reflection.klass
   end
+
+  def test_valid_options
+    assert @klass.build(Product, :inventory, class_name: "Product")
+    assert @klass.build(Product, :inventory, foreign_key: "product_id")
+    assert @klass.build(Product, :inventory, primary_key: "id")
+
+    assert_raise ArgumentError do
+      @klass.build(Product, :inventory, soo_invalid: true)
+    end
+  end
 end