Allow specify fixtures to be ignored

Allow specifying what fixtures can be ignored by setting
`ignore` in fixtures YAML file:

    # users.yml
    _fixture:
      ignore:
        - base

    base: &base
      admin: false
      introduction: "This is a default description"

    admin:
      <<: *base
      admin: true

    visitor:
      <<: *base

In the above example, "base" fixture will be ignored when creating
users fixture. This is helpful when you want to inherit attributes
and it makes your fixtures more "DRY".

1 files changed, 42 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 046ed0e95c..3df4b3c87f 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -420,6 +420,29 @@ module ActiveRecord
   #
   # Any fixture labeled "DEFAULTS" is safely ignored.
   #
+  # Besides using "DEFAULTS", you can also specify what fixtures will
+  # be ignored by setting "ignore" in "_fixture" section.
+  #
+  #   # users.yml
+  #   _fixture:
+  #     ignore:
+  #       - base
+  #     # or use "ignore: base" when there is only one fixture needs to be ignored.
+  #
+  #   base: &base
+  #     admin: false
+  #     introduction: "This is a default description"
+  #
+  #   admin:
+  #     <<: *base
+  #     admin: true
+  #
+  #   visitor:
+  #     <<: *base
+  #
+  # In the above example, 'base' will be ignored when creating fixtures.
+  # This can be used for common attributes inheriting.
+  #
   # == Configure the fixture model class
   #
   # It's possible to set the fixture's model class directly in the YAML file.
@@ -614,7 +637,7 @@ module ActiveRecord
         end
     end
 
-    attr_reader :table_name, :name, :fixtures, :model_class, :config
+    attr_reader :table_name, :name, :fixtures, :model_class, :ignored_fixtures, :config
 
     def initialize(_, name, class_name, path, config = ActiveRecord::Base)
       @name     = name
@@ -647,8 +670,8 @@ module ActiveRecord
     # Returns a hash of rows to be inserted. The key is the table, the value is
     # a list of rows to insert to that table.
     def table_rows
-      # allow a standard key to be used for doing defaults in YAML
-      fixtures.delete("DEFAULTS")
+      # allow specifying fixtures to be ignored by setting `ignore` in `_fixture` section
+      fixtures.except!(*ignored_fixtures)
 
       TableRows.new(
         table_name,
@@ -667,6 +690,21 @@ module ActiveRecord
         end
       end
 
+      def ignored_fixtures=(base)
+        @ignored_fixtures =
+            case base
+            when Array
+              base
+            when String
+              [base]
+            else
+              []
+            end
+
+        @ignored_fixtures << "DEFAULTS" unless @ignored_fixtures.include?("DEFAULTS")
+        @ignored_fixtures.compact
+      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.
@@ -678,6 +716,7 @@ module ActiveRecord
         yaml_files.each_with_object({}) do |file, fixtures|
           FixtureSet::File.open(file) do |fh|
             self.model_class ||= fh.model_class if fh.model_class
+            self.ignored_fixtures ||= fh.ignored_fixtures
             fh.each do |fixture_name, row|
               fixtures[fixture_name] = ActiveRecord::Fixture.new(row, model_class)
             end