Allow fixtures YAML files to set the model class in the file itself

Currently, `set_fixture_class` is only available using the
`TestFixtures` concern and it is ignored for `rake db:fixtures:load`.
Using the correct model class, it is possible for the fixture load
to also load the associations from the YAML files (e.g., `:belongs_to`
and `:has_many`).

activerecord/CHANGELOG.md

@@ -1,3 +1,18 @@
+*   Allow fixtures YAML files to set the model class in the file itself.
+
+    To load the fixtures file `accounts.yml` as the `User` model, use:
+
+        ```yaml
+          _fixture:
+            model_class: User
+          david:
+            name: David
+        ```
+
+    Fixes #9516.
+
+    *Roque Pinel*
+
 *   Correct query for PostgreSQL 8.2 compatibility.
 
     *Ben Murphy*, *Matthew Draper*

activerecord/lib/active_record/fixture_set/file.rb

@@ -18,23 +18,34 @@ def self.open(file)
       def initialize(file)
         @file = file
         @rows = nil
+        @raw_rows = nil
+        @model_class = nil
       end
 
       def each(&block)
         rows.each(&block)
       end
 
+      def model_class
+        return @model_class if @model_class
+        row = raw_rows.find { |fixture_name, _| fixture_name == '_fixture' }
+        @model_class = row.last['model_class'] if row
+      end
 
       private
         def rows
-          return @rows if @rows
+          @rows ||= raw_rows.reject { |fixture_name, _| fixture_name == '_fixture' }
+        end
+
+        def raw_rows
+          return @raw_rows if @raw_rows
 
           begin
             data = YAML.load(render(IO.read(@file)))
           rescue ArgumentError, Psych::SyntaxError => error
             raise Fixture::FormatError, "a YAML error occurred parsing #{@file}. Please note that YAML must be consistently indented using spaces. Tabs are not allowed. Please have a look at http://www.yaml.org/faq.html\nThe exact error was:\n  #{error.class}: #{error}", error.backtrace
           end
-          @rows = data ? validate(data).to_a : []
+          @raw_rows = data ? validate(data).to_a : []
         end
 
         def render(content)

activerecord/lib/active_record/fixtures.rb

@@ -395,6 +395,23 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError #:nodoc:
   #     <<: *DEFAULTS
   #
   # Any fixture labeled "DEFAULTS" is safely ignored.
+  #
+  # == Support to custom model class
+  #
+  # You can also set the model class in your fixtures YAML file.
+  # This is helpful when fixtures are being loaded outside tests and
+  # you cannot use +set_fixture_class+, e.g., when running
+  # <tt>rake db:fixtures:load</tt>.
+  #
+  # To load the fixtures file +test/fixtures/accounts.yml+ as the +User+
+  # model, use:
+  #
+  #   _fixture:
+  #     model_class: User
+  #   david:
+  #     name: David
+  #
+  # Any fixture labeled "_fixture" is safely ignored.
   class FixtureSet
     #--
     # An instance of FixtureSet is normally stored in a single YAML file and
@@ -578,21 +595,16 @@ def initialize(connection, name, class_name, path, config = ActiveRecord::Base)
       @name     = name
       @path     = path
       @config   = config
-      @model_class = nil
 
-      if class_name.is_a?(Class) # TODO: Should be an AR::Base type class, or any?
-        @model_class = class_name
-      else
-        @model_class = class_name.safe_constantize if class_name
-      end
+      self.model_class = class_name
+
+      @fixtures = read_fixture_files(path)
 
       @connection  = connection
 
       @table_name = ( model_class.respond_to?(:table_name) ?
                       model_class.table_name :
                       self.class.default_fixture_table_name(name, config) )
-
-      @fixtures = read_fixture_files path, @model_class
     end
 
     def [](x)
@@ -761,13 +773,25 @@ def column_names
         @column_names ||= @connection.columns(@table_name).collect(&:name)
       end
 
-      def read_fixture_files(path, model_class)
+      def model_class=(class_name)
+        if class_name.is_a?(Class) # TODO: Should be an AR::Base type class, or any?
+          @model_class = class_name
+        else
+          @model_class = class_name.safe_constantize if class_name
+        end
+      end
+
+      # Loads the fixtures from the YAML file at +path+.
+      # If the file sets the +model_class+ and current instance value is not set,
+      # it uses the file value.
+      def read_fixture_files(path)
         yaml_files = Dir["#{path}/{**,*}/*.yml"].select { |f|
           ::File.file?(f)
         } + [yaml_file_path(path)]
 
         yaml_files.each_with_object({}) do |file, fixtures|
           FixtureSet::File.open(file) do |fh|
+            self.model_class ||= fh.model_class if fh.model_class
             fh.each do |fixture_name, row|
               fixtures[fixture_name] = ActiveRecord::Fixture.new(row, model_class)
             end

activerecord/test/cases/fixture_set/file_test.rb

@@ -123,6 +123,16 @@ def test_independent_render_contexts
         end
       end
 
+      def test_fixture_model_class_and_rows
+        File.open(::File.join(FIXTURES_ROOT, 'other_posts.yml')) do |fh|
+          assert_equal 'Post', fh.model_class
+
+          fixture_names = []
+          fh.each { |fixture_name, _| fixture_names << fixture_name }
+          assert_equal ['second_welcome'], fixture_names
+        end
+      end
+
       private
       def tmp_yaml(name, contents)
         t = Tempfile.new name

activerecord/test/cases/fixtures_test.rb

@@ -7,15 +7,16 @@
 require 'models/book'
 require 'models/bulb'
 require 'models/category'
+require 'models/comment'
 require 'models/company'
 require 'models/computer'
 require 'models/course'
 require 'models/developer'
+require 'models/doubloon'
 require 'models/joke'
 require 'models/matey'
 require 'models/parrot'
 require 'models/pirate'
-require 'models/doubloon'
 require 'models/post'
 require 'models/randomly_named_c1'
 require 'models/reply'
@@ -514,6 +515,38 @@ def test_fixture_methods_can_be_overridden
   end
 end
 
+class FixtureWithSetModelClassTest < ActiveRecord::TestCase
+  fixtures :other_posts, :other_comments
+
+  # Set to false to blow away fixtures cache and ensure our fixtures are loaded
+  # and thus takes into account the +set_model_class+.
+  self.use_transactional_tests = false
+
+  def test_table_method
+    assert_kind_of Post, other_posts(:second_welcome)
+  end
+
+  def test_loads_the_associations_to_fixtures_with_set_model_class
+    post = other_posts(:second_welcome)
+    comment = other_comments(:second_greetings)
+    assert_equal [comment], post.comments
+    assert_equal post, comment.post
+  end
+end
+
+class SetFixtureClassPrevailsTest < ActiveRecord::TestCase
+  set_fixture_class bad_posts: Post
+  fixtures :bad_posts
+
+  # Set to false to blow away fixtures cache and ensure our fixtures are loaded
+  # and thus takes into account the +set_model_class+.
+  self.use_transactional_tests = false
+
+  def test_table_method2
+    assert_kind_of Post, bad_posts(:bad_welcome)
+  end
+end
+
 class CheckSetTableNameFixturesTest < ActiveRecord::TestCase
   set_fixture_class :funny_jokes => Joke
   fixtures :funny_jokes

activerecord/test/fixtures/bad_posts.yml

@@ -0,0 +1,10 @@
+# Please do not use this fixture without `set_fixture_class` as Post
+
+_fixture:
+  model_class: BadPostModel
+
+bad_welcome:
+  author_id: 1
+  title: Welcome to the another weblog
+  body: It's really nice today
+  type: Post

activerecord/test/fixtures/other_comments.yml

@@ -0,0 +1,7 @@
+_fixture:
+  model_class: Comment
+
+second_greetings:
+  post: second_welcome
+  body: Thank you for the second welcome
+  type: Comment

activerecord/test/fixtures/other_posts.yml

@@ -0,0 +1,8 @@
+_fixture:
+  model_class: Post
+
+second_welcome:
+  author_id: 1
+  title: Welcome to the another weblog
+  body: It's really nice today
+  type: Post