Added #or to ActiveRecord::Relation

    Post.where('id = 1').or(Post.where('id = 2'))
    # => SELECT * FROM posts WHERE (id = 1) OR (id = 2)

[Matthew Draper & Gael Muller]

activerecord/CHANGELOG.md

@@ -1,3 +1,13 @@
+*   Added the `#or` method on ActiveRecord::Relation, allowing use of the OR
+    operator to combine WHERE or HAVING clauses.
+
+    Example:
+
+        Post.where('id = 1').or(Post.where('id = 2'))
+        # => SELECT * FROM posts WHERE (id = 1) OR (id = 2)
+
+    *Sean Griffin*, *Matthew Draper*, *Gael Muller*, *Olivier El Mekki*
+
 *   Don't define autosave association callbacks twice from
     `accepts_nested_attributes_for`.
 

activerecord/lib/active_record/null_relation.rb

@@ -75,5 +75,13 @@ def calculate(operation, _column_name)
     def exists?(_id = false)
       false
     end
+
+    def or(other)
+      if other.is_a?(NullRelation)
+        super
+      else
+        other.or(self)
+      end
+    end
   end
 end

activerecord/lib/active_record/querying.rb

@@ -7,7 +7,7 @@ module Querying
     delegate :find_by, :find_by!, to: :all
     delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, to: :all
     delegate :find_each, :find_in_batches, to: :all
-    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins,
+    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :or,
              :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly,
              :having, :create_with, :uniq, :distinct, :references, :none, :unscope, to: :all
     delegate :count, :average, :minimum, :maximum, :sum, :calculate, to: :all

activerecord/lib/active_record/relation/query_methods.rb

@@ -582,6 +582,65 @@ def rewhere(conditions)
       unscope(where: conditions.keys).where(conditions)
     end
 
+    # Returns a new relation, which is the logical union of this relation and the one passed as an
+    # argument.
+    #
+    # 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.
+    #
+    #    Post.where("id = 1").or(Post.where("id = 2"))
+    #    # SELECT `posts`.* FROM `posts`  WHERE (('id = 1' OR 'id = 2'))
+    #
+    def or(other)
+      spawn.or!(other)
+    end
+
+    def or!(other)
+      combining = group_values.any? ? :having : :where
+
+      unless structurally_compatible?(other, combining)
+        raise ArgumentError, 'Relation passed to #or must be structurally compatible'
+      end
+
+      unless other.is_a?(NullRelation)
+        left_values = send("#{combining}_values")
+        right_values = other.send("#{combining}_values")
+
+        common = left_values & right_values
+        mine = left_values - common
+        theirs = right_values - common
+
+        if mine.any? && theirs.any?
+          mine = mine.map { |x| String === x ? Arel.sql(x) : x }
+          theirs = theirs.map { |x| String === x ? Arel.sql(x) : x }
+
+          mine = [Arel::Nodes::And.new(mine)] if mine.size > 1
+          theirs = [Arel::Nodes::And.new(theirs)] if theirs.size > 1
+
+          common << Arel::Nodes::Or.new(mine.first, theirs.first)
+        end
+
+        send("#{combining}_values=", common)
+      end
+
+      self
+    end
+
+    def structurally_compatible?(other, allowed_to_vary)
+      Relation::SINGLE_VALUE_METHODS.all? do |name|
+        send("#{name}_value") == other.send("#{name}_value")
+      end &&
+        (Relation::MULTI_VALUE_METHODS - [allowed_to_vary, :extending]).all? do |name|
+          send("#{name}_values") == other.send("#{name}_values")
+        end &&
+        (extending_values - [NullRelation]) == (other.extending_values - [NullRelation]) &&
+        !limit_value &&
+        !offset_value &&
+        !uniq_value
+    end
+    private :structurally_compatible?
+
     # Allows to specify a HAVING clause. Note that you can't use HAVING
     # without also specifying a GROUP clause.
     #

activerecord/test/cases/relation/or_test.rb

@@ -0,0 +1,81 @@
+require "cases/helper"
+require 'models/post'
+
+module ActiveRecord
+  class OrTest < ActiveRecord::TestCase
+    fixtures :posts
+
+    def test_or_with_relation
+      expected = Post.where('id = 1 or id = 2').to_a
+      assert_equal expected, Post.where('id = 1').or(Post.where('id = 2')).to_a
+    end
+
+    def test_or_identity
+      expected = Post.where('id = 1').to_a
+      assert_equal expected, Post.where('id = 1').or(Post.where('id = 1')).to_a
+    end
+
+    def test_or_with_null_left
+      expected = Post.where('id = 1').to_a
+      assert_equal expected, Post.none.or(Post.where('id = 1')).to_a
+    end
+
+    def test_or_with_null_right
+      expected = Post.where('id = 1').to_a
+      assert_equal expected, Post.where('id = 1').or(Post.none).to_a
+    end
+
+    def test_or_with_null_both
+      expected = Post.none.to_a
+      assert_equal expected, Post.none.or(Post.none).to_a
+    end
+
+    def test_or_without_left_where
+      expected = Post.all.to_a
+      assert_equal expected, Post.or(Post.where('id = 1')).to_a
+    end
+
+    def test_or_without_right_where
+      expected = Post.all.to_a
+      assert_equal expected, Post.where('id = 1').or(Post.all).to_a
+    end
+
+    def test_or_preserves_other_querying_methods
+      expected = Post.where('id = 1 or id = 2 or id = 3').order('body asc').to_a
+      partial = Post.order('body asc')
+      assert_equal expected, partial.where('id = 1').or(partial.where(:id => [2, 3])).to_a
+      assert_equal expected, Post.order('body asc').where('id = 1').or(Post.order('body asc').where(:id => [2, 3])).to_a
+    end
+
+    def test_or_with_incompatible_relations
+      assert_raises ArgumentError do
+        Post.order('body asc').where('id = 1').or(Post.order('id desc').where(:id => [2, 3])).to_a
+      end
+    end
+
+    def test_or_when_grouping
+      groups = Post.where('id < 10').group('body').select('body, COUNT(*) AS c')
+      expected = groups.having("COUNT(*) > 1 OR body like 'Such%'").to_a.map {|o| [o.body, o.c] }
+      assert_equal expected, groups.having('COUNT(*) > 1').or(groups.having("body like 'Such%'")).to_a.map {|o| [o.body, o.c] }
+    end
+
+    def test_or_with_named_scope
+      expected = Post.where("id = 1 or body LIKE '\%a\%'").to_a
+      assert_equal expected, Post.where('id = 1').or(Post.containing_the_letter_a)
+    end
+
+    def test_or_inside_named_scope
+      expected = Post.where("body LIKE '\%a\%' OR title LIKE ?", "%'%").order('id DESC').to_a
+      assert_equal expected, Post.order(id: :desc).typographically_interesting
+    end
+
+    def test_or_on_loaded_relation
+      expected = Post.where('id = 1 or id = 2').to_a
+      p = Post.where('id = 1')
+      p.load
+      assert_equal p.loaded?, true
+      assert_equal expected, p.or(Post.where('id = 2')).to_a
+    end
+
+  end
+end

activerecord/test/models/post.rb

@@ -18,6 +18,7 @@ def greeting
   end
 
   scope :containing_the_letter_a, -> { where("body LIKE '%a%'") }
+  scope :titled_with_an_apostrophe, -> { where("title LIKE '%''%'") }
   scope :ranked_by_comments,      -> { order("comments_count DESC") }
 
   scope :limit_by, lambda {|l| limit(l) }
@@ -43,6 +44,8 @@ def first_comment
   scope :tagged_with, ->(id) { joins(:taggings).where(taggings: { tag_id: id }) }
   scope :tagged_with_comment, ->(comment) { joins(:taggings).where(taggings: { comment: comment }) }
 
+  scope :typographically_interesting, -> { containing_the_letter_a.or(titled_with_an_apostrophe) }
+
   has_many   :comments do
     def find_most_recent
       order("id DESC").first