Add ActiveRecord::Relation#uniq for toggling DISTINCT in the SQL query

7 files changed, 67 insertions, 9 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 426f6b48b3..2524082062 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,21 @@
 ## Rails 3.2.0 (unreleased) ##
 
+*   Add ActiveRecord::Relation#uniq for generating unique queries.
+
+    Before:
+
+        Client.select('DISTINCT name')
+
+    After:
+
+        Client.select(:name).uniq
+
+    This also allows you to revert the unqueness in a relation:
+
+        Client.select(:name).uniq.uniq(false)
+
+    *Jon Leighton*
+
 *   Support index sort order in sqlite, mysql and postgres adapters. *Vlad Jebelev*
 
 *   Allow the :class_name option for associations to take a symbol (:Client) in addition to
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 360e494af1..455b299270 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -445,7 +445,9 @@ module ActiveRecord #:nodoc:
       delegate :first_or_create, :first_or_create!, :first_or_initialize, :to => :scoped
       delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, :to => :scoped
       delegate :find_each, :find_in_batches, :to => :scoped
-      delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :where, :preload, :eager_load, :includes, :from, :lock, :readonly, :having, :create_with, :to => :scoped
+      delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins,
+               :where, :preload, :eager_load, :includes, :from, :lock, :readonly,
+               :having, :create_with, :uniq, :to => :scoped
       delegate :count, :average, :minimum, :maximum, :sum, :calculate, :to => :scoped
 
       # Executes a custom SQL query against your database and returns all the results. The results will
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index ecefaa633c..3baf9b3f49 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -7,7 +7,7 @@ module ActiveRecord
     JoinOperation = Struct.new(:relation, :join_class, :on)
     ASSOCIATION_METHODS = [:includes, :eager_load, :preload]
     MULTI_VALUE_METHODS = [:select, :group, :order, :joins, :where, :having, :bind]
-    SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reorder, :reverse_order]
+    SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reorder, :reverse_order, :uniq]
 
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches
 
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 670ba0987d..c281bead0d 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -9,7 +9,8 @@ module ActiveRecord
                   :select_values, :group_values, :order_values, :joins_values,
                   :where_values, :having_values, :bind_values,
                   :limit_value, :offset_value, :lock_value, :readonly_value, :create_with_value,
-                  :from_value, :reorder_value, :reverse_order_value
+                  :from_value, :reorder_value, :reverse_order_value,
+                  :uniq_value
 
     def includes(*args)
       args.reject! {|a| a.blank? }
@@ -38,7 +39,7 @@ module ActiveRecord
     end
 
     # Works in two unique ways.
-    # 
+    #
     # First: takes a block so it can be used just like Array#select.
     #
     #   Model.scoped.select { |m| m.field == value }
@@ -176,9 +177,25 @@ module ActiveRecord
       relation
     end
 
+    # Specifies whether the records should be unique or not. For example:
+    #
+    #   User.select(:name)
+    #   # => Might return two records with the same name
+    #
+    #   User.select(:name).uniq
+    #   # => Returns 1 record per unique name
+    #
+    #   User.select(:name).uniq.uniq(false)
+    #   # => You can also remove the uniqueness
+    def uniq(value = true)
+      relation = clone
+      relation.uniq_value = value
+      relation
+    end
+
     # Used to extend a scope with additional methods, either through
-    # a module or through a block provided. 
-    # 
+    # a module or through a block provided.
+    #
     # The object returned is a relation, which can be further extended.
     #
     # === Using a module
@@ -200,7 +217,7 @@ module ActiveRecord
     #
     #   scope = Model.scoped.extending do
     #     def page(number)
-    #       # pagination code goes here 
+    #       # pagination code goes here
     #     end
     #   end
     #   scope.page(params[:page])
@@ -209,7 +226,7 @@ module ActiveRecord
     #
     #   scope = Model.scoped.extending(Pagination) do
     #     def per_page(number)
-    #       # pagination code goes here 
+    #       # pagination code goes here
     #     end
     #   end
     def extending(*modules)
@@ -252,6 +269,7 @@ module ActiveRecord
 
       build_select(arel, @select_values.uniq)
 
+      arel.distinct(@uniq_value)
       arel.from(@from_value) if @from_value
       arel.lock(@lock_value) if @lock_value
 
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 12c1cfb30e..fdb656fe13 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -1935,4 +1935,10 @@ class BasicsTest < ActiveRecord::TestCase
     dev.update_attribute(:updated_at, nil)
     assert_match(/\/#{dev.id}$/, dev.cache_key)
   end
+
+  def test_uniq_delegates_to_scoped
+    scope = stub
+    Bird.stubs(:scoped).returns(mock(:uniq => scope))
+    assert_equal scope, Bird.uniq
+  end
 end
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index b23ead6feb..715a378431 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -20,7 +20,7 @@ module ActiveRecord
     end
 
     def test_single_values
-      assert_equal [:limit, :offset, :lock, :readonly, :from, :reorder, :reverse_order].map(&:to_s).sort,
+      assert_equal [:limit, :offset, :lock, :readonly, :from, :reorder, :reverse_order, :uniq].map(&:to_s).sort,
         Relation::SINGLE_VALUE_METHODS.map(&:to_s).sort
     end
 
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 95408a5f29..bf1eb6386a 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1148,4 +1148,20 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal posts(:thinking), comments(:more_greetings).post
     assert_equal posts(:welcome),  comments(:greetings).post
   end
+
+  def test_uniq
+    tag1 = Tag.create(:name => 'Foo')
+    tag2 = Tag.create(:name => 'Foo')
+
+    query = Tag.select(:name).where(:id => [tag1.id, tag2.id])
+
+    assert_equal ['Foo', 'Foo'], query.map(&:name)
+    assert_sql(/DISTINCT/) do
+      assert_equal ['Foo'], query.uniq.map(&:name)
+    end
+    assert_sql(/DISTINCT/) do
+      assert_equal ['Foo'], query.uniq(true).map(&:name)
+    end
+    assert_equal ['Foo', 'Foo'], query.uniq(true).uniq(false).map(&:name)
+  end
 end