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]

3 files changed, 68 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index b406da14dc..802adca908 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -75,5 +75,13 @@ module ActiveRecord
     def exists?(_id = false)
       false
     end
+
+    def or(other)
+      if other.is_a?(NullRelation)
+        super
+      else
+        other.or(self)
+      end
+    end
   end
 end
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 91c9a0db99..4e597590e9 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -7,7 +7,7 @@ module ActiveRecord
     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
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 0078b0f32e..78ee8b4580 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -582,6 +582,65 @@ module ActiveRecord
       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.
     #