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".

6 files changed, 111 insertions, 5 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 366032c734..7f2071189b 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Allow specifying fixtures to be ignored by setting `ignore` in YAML file's '_fixture' section.
+
+    *Tongfei Gao*
+
 *   Make the DATABASE_URL env variable only affect the primary connection. Add new env variables for multiple databases.
 
     *John Crepezzi*, *Eileen Uchitelle*
diff --git a/activerecord/lib/active_record/fixture_set/file.rb b/activerecord/lib/active_record/fixture_set/file.rb
index f1ea0e022f..b2030a5bb9 100644
--- a/activerecord/lib/active_record/fixture_set/file.rb
+++ b/activerecord/lib/active_record/fixture_set/file.rb
@@ -29,6 +29,10 @@ module ActiveRecord
         config_row["model_class"]
       end
 
+      def ignored_fixtures
+        config_row["ignore"]
+      end
+
       private
         def rows
           @rows ||= raw_rows.reject { |fixture_name, _| fixture_name == "_fixture" }
@@ -40,7 +44,7 @@ module ActiveRecord
             if row
               row.last
             else
-              { 'model_class': nil }
+              { 'model_class': nil, 'ignore': nil }
             end
           end
         end
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
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index a7f01e898e..7ad032a632 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -1279,6 +1279,33 @@ class CustomNameForFixtureOrModelTest < ActiveRecord::TestCase
   end
 end
 
+class IgnoreFixturesTest < ActiveRecord::TestCase
+  fixtures :other_books, :parrots
+
+  test "ignores books fixtures" do
+    assert_raise(StandardError) { other_books(:published) }
+    assert_raise(StandardError) { other_books(:published_paperback) }
+    assert_raise(StandardError) { other_books(:published_ebook) }
+
+    assert_equal 2, Book.count
+    assert_equal "Agile Web Development with Rails", other_books(:awdr).name
+    assert_equal "published", other_books(:awdr).status
+    assert_equal "paperback", other_books(:awdr).format
+    assert_equal "english", other_books(:awdr).language
+
+    assert_equal "Ruby for Rails", other_books(:rfr).name
+    assert_equal "ebook", other_books(:rfr).format
+    assert_equal "published", other_books(:rfr).status
+  end
+
+  test "ignores parrots fixtures" do
+    assert_raise(StandardError) { parrots(:DEFAULT) }
+    assert_raise(StandardError) { parrots(:DEAD_PARROT) }
+
+    assert_equal "DeadParrot", parrots(:polly).parrot_sti_class
+  end
+end
+
 class FixturesWithDefaultScopeTest < ActiveRecord::TestCase
   fixtures :bulbs
 
diff --git a/activerecord/test/fixtures/other_books.yml b/activerecord/test/fixtures/other_books.yml
new file mode 100644
index 0000000000..62806c03d7
--- /dev/null
+++ b/activerecord/test/fixtures/other_books.yml
@@ -0,0 +1,26 @@
+_fixture:
+  model_class: Book
+  ignore:
+    - PUBLISHED
+    - PUBLISHED_PAPERBACK
+    - PUBLISHED_EBOOK
+
+PUBLISHED: &PUBLISHED
+  status: :published
+
+PUBLISHED_PAPERBACK: &PUBLISHED_PAPERBACK
+  <<: *PUBLISHED
+  format: "paperback"
+  language: :english
+
+PUBLISHED_EBOOK: &PUBLISHED_EBOOK
+  <<: *PUBLISHED
+  format: "ebook"
+
+awdr:
+  <<: *PUBLISHED_PAPERBACK
+  name: "Agile Web Development with Rails"
+
+rfr:
+  <<: *PUBLISHED_EBOOK
+  name: "Ruby for Rails"
diff --git a/activerecord/test/fixtures/parrots.yml b/activerecord/test/fixtures/parrots.yml
index 8425ef98e0..4f0a090e03 100644
--- a/activerecord/test/fixtures/parrots.yml
+++ b/activerecord/test/fixtures/parrots.yml
@@ -1,3 +1,9 @@
+_fixture:
+  ignore: DEAD_PARROT
+
+DEAD_PARROT: &DEAD_PARROT
+  parrot_sti_class: DeadParrot
+
 george:
   name: "Curious George"
   treasures: diamond, sapphire
@@ -17,7 +23,7 @@ polly:
   name: $LABEL
   killer: blackbeard
   treasures: sapphire, ruby
-  parrot_sti_class: DeadParrot
+  <<: *DEAD_PARROT
 
 DEFAULTS: &DEFAULTS
   treasures: sapphire, ruby