deprecate Relation#uniq use Relation#distinct instead.

See #9683 for the reasons we switched to `distinct`.

Here is the discussion that triggered the actual deprecation #20198.

`uniq`, `uniq!` and `uniq_value` are still around.
They will be removed in the next minor release after Rails 5.

Author: senny

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Deprecate `Relation#uniq` use `Relation#distinct` instead.
+
+    See #9683.
+
+    *Yves Senn*
+
 *   Allow single table inheritance instantiation to work when storing
     demodulized class names.
 

activerecord/lib/active_record/associations.rb

@@ -266,7 +266,6 @@ def association_instance_set(name, association)
     #   others.find(*args)                |   X   |    X     |    X
     #   others.exists?                    |   X   |    X     |    X
     #   others.distinct                   |   X   |    X     |    X
-    #   others.uniq                       |   X   |    X     |    X
     #   others.reset                      |   X   |    X     |    X
     #
     # === Overriding generated methods

activerecord/lib/active_record/relation.rb

@@ -9,7 +9,7 @@ class Relation
                             :extending, :unscope]
 
     SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering,
-                            :reverse_order, :distinct, :create_with, :uniq]
+                            :reverse_order, :distinct, :create_with]
     CLAUSE_METHODS = [:where, :having, :from]
     INVALID_METHODS_FOR_DELETE_ALL = [:limit, :distinct, :offset, :group, :having]
 
@@ -618,6 +618,7 @@ def joined_includes_values
     def uniq_value
       distinct_value
     end
+    deprecate uniq_value: :distinct_value
 
     # Compares two relations for equality.
     def ==(other)

activerecord/lib/active_record/relation/query_methods.rb

@@ -587,7 +587,7 @@ def rewhere(conditions)
     #
     # The two relations must be structurally compatible: they must be scoping the same model, and
     # they must differ only by +where+ (if no +group+ has been defined) or +having+ (if a +group+ is
-    # present). Neither relation may have a +limit+, +offset+, or +uniq+ set.
+    # present). Neither relation may have a +limit+, +offset+, or +distinct+ set.
     #
     #    Post.where("id = 1").or(Post.where("id = 2"))
     #    # SELECT `posts`.* FROM `posts`  WHERE (('id = 1' OR 'id = 2'))
@@ -790,13 +790,15 @@ def distinct(value = true)
       spawn.distinct!(value)
     end
     alias uniq distinct
+    deprecate uniq: :distinct
 
     # Like #distinct, but modifies relation in place.
     def distinct!(value = true) # :nodoc:
       self.distinct_value = value
       self
     end
     alias uniq! distinct!
+    deprecate uniq!: :distinct!
 
     # Used to extend a scope with additional methods, either through
     # a module or through a block provided.

activerecord/test/cases/associations/eager_test.rb

@@ -1167,7 +1167,7 @@ def test_preloading_through_empty_belongs_to
     assert_no_queries { assert client.accounts.empty? }
   end
 
-  def test_preloading_has_many_through_with_uniq
+  def test_preloading_has_many_through_with_distinct
     mary = Author.includes(:unique_categorized_posts).where(:id => authors(:mary).id).first
     assert_equal 1, mary.unique_categorized_posts.length
     assert_equal 1, mary.unique_categorized_post_ids.length

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -234,7 +234,7 @@ def test_habtm_saving_multiple_relationships
     assert_equal developers, new_project.developers
   end
 
-  def test_habtm_unique_order_preserved
+  def test_habtm_distinct_order_preserved
     assert_equal developers(:poor_jamis, :jamis, :david), projects(:active_record).non_unique_developers
     assert_equal developers(:poor_jamis, :jamis, :david), projects(:active_record).developers
   end
@@ -339,7 +339,7 @@ def test_creation_respects_hash_condition
     assert_equal  'Yet Another Testing Title', another_post.title
   end
 
-  def test_uniq_after_the_fact
+  def test_distinct_after_the_fact
     dev = developers(:jamis)
     dev.projects << projects(:active_record)
     dev.projects << projects(:active_record)
@@ -348,13 +348,13 @@ def test_uniq_after_the_fact
     assert_equal 1, dev.projects.distinct.size
   end
 
-  def test_uniq_before_the_fact
+  def test_distinct_before_the_fact
     projects(:active_record).developers << developers(:jamis)
     projects(:active_record).developers << developers(:david)
     assert_equal 3, projects(:active_record, :reload).developers.size
   end
 
-  def test_uniq_option_prevents_duplicate_push
+  def test_distinct_option_prevents_duplicate_push
     project = projects(:active_record)
     project.developers << developers(:jamis)
     project.developers << developers(:david)
@@ -365,7 +365,7 @@ def test_uniq_option_prevents_duplicate_push
     assert_equal 3, project.developers.size
   end
 
-  def test_uniq_when_association_already_loaded
+  def test_distinct_when_association_already_loaded
     project = projects(:active_record)
     project.developers << [ developers(:jamis), developers(:david), developers(:jamis), developers(:david) ]
     assert_equal 3, Project.includes(:developers).find(project.id).developers.size

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -960,7 +960,7 @@ def test_create_has_many_through_with_default_scope_on_join_model
     assert_equal 1, category.categorizations.where(:special => true).count
   end
 
-  def test_joining_has_many_through_with_uniq
+  def test_joining_has_many_through_with_distinct
     mary = Author.joins(:unique_categorized_posts).where(:id => authors(:mary).id).first
     assert_equal 1, mary.unique_categorized_posts.length
     assert_equal 1, mary.unique_categorized_post_ids.length

activerecord/test/cases/associations/join_model_test.rb

@@ -35,12 +35,12 @@ def test_inherited_has_many
     assert categories(:sti_test).authors.include?(authors(:mary))
   end
 
-  def test_has_many_uniq_through_join_model
+  def test_has_many_distinct_through_join_model
     assert_equal 2, authors(:mary).categorized_posts.size
     assert_equal 1, authors(:mary).unique_categorized_posts.size
   end
 
-  def test_has_many_uniq_through_count
+  def test_has_many_distinct_through_count
     author = authors(:mary)
     assert !authors(:mary).unique_categorized_posts.loaded?
     assert_queries(1) { assert_equal 1, author.unique_categorized_posts.count }
@@ -49,7 +49,7 @@ def test_has_many_uniq_through_count
     assert !authors(:mary).unique_categorized_posts.loaded?
   end
 
-  def test_has_many_uniq_through_find
+  def test_has_many_distinct_through_find
     assert_equal 1, authors(:mary).unique_categorized_posts.to_a.size
   end
 
@@ -625,7 +625,7 @@ def test_has_many_through_has_many_with_sti
     assert_equal [comments(:does_it_hurt)], authors(:david).special_post_comments
   end
 
-  def test_uniq_has_many_through_should_retain_order
+  def test_distinct_has_many_through_should_retain_order
     comment_ids = authors(:david).comments.map(&:id)
     assert_equal comment_ids.sort, authors(:david).ordered_uniq_comments.map(&:id)
     assert_equal comment_ids.sort.reverse, authors(:david).ordered_uniq_comments_desc.map(&:id)

activerecord/test/cases/base_test.rb

@@ -1411,15 +1411,13 @@ def test_touch_should_raise_error_on_a_new_object
   end
 
   def test_uniq_delegates_to_scoped
-    scope = stub
-    Bird.stubs(:all).returns(mock(:uniq => scope))
-    assert_equal scope, Bird.uniq
+    assert_deprecated do
+      assert_equal Bird.all.distinct, Bird.uniq
+    end
   end
 
   def test_distinct_delegates_to_scoped
-    scope = stub
-    Bird.stubs(:all).returns(mock(:distinct => scope))
-    assert_equal scope, Bird.distinct
+    assert_equal Bird.all.distinct, Bird.distinct
   end
 
   def test_table_name_with_2_abstract_subclasses

activerecord/test/cases/calculations_test.rb

@@ -359,7 +359,10 @@ def test_count_with_column_parameter
 
   def test_count_with_distinct
     assert_equal 4, Account.select(:credit_limit).distinct.count
-    assert_equal 4, Account.select(:credit_limit).uniq.count
+
+    assert_deprecated do
+      assert_equal 4, Account.select(:credit_limit).uniq.count
+    end
   end
 
   def test_count_with_aliased_attribute
@@ -504,8 +507,8 @@ def test_pluck_type_cast
     assert_equal [ topic.written_on ], relation.pluck(:written_on)
   end
 
-  def test_pluck_and_uniq
-    assert_equal [50, 53, 55, 60], Account.order(:credit_limit).uniq.pluck(:credit_limit)
+  def test_pluck_and_distinct
+    assert_equal [50, 53, 55, 60], Account.order(:credit_limit).distinct.pluck(:credit_limit)
   end
 
   def test_pluck_in_relation