Move Relation#spawn and Relation#merge to a separate module

1 files changed, 49 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
new file mode 100644
index 0000000000..4a64f0c6a9
--- /dev/null
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -0,0 +1,49 @@
+module ActiveRecord
+  module SpawnMethods
+    def spawn(relation = @relation)
+      relation = Relation.new(@klass, relation)
+      relation.readonly = @readonly
+      relation.preload_associations = @preload_associations
+      relation.eager_load_associations = @eager_load_associations
+      relation.include_associations = @include_associations
+      relation.table = table
+      relation
+    end
+
+    def merge(r)
+      raise ArgumentError, "Cannot merge a #{r.klass.name} relation with #{@klass.name} relation" if r.klass != @klass
+
+      merged_relation = spawn(table).eager_load(r.eager_load_associations).preload(r.preload_associations).includes(r.include_associations)
+      merged_relation.readonly = r.readonly
+
+      [self.relation, r.relation].each do |arel|
+        merged_relation = merged_relation.
+          joins(arel.joins(arel)).
+          group(arel.groupings).
+          limit(arel.taken).
+          offset(arel.skipped).
+          select(arel.send(:select_clauses)).
+          from(arel.sources)
+      end
+
+      relation_order = r.send(:order_clause)
+      merged_order = relation_order.present? ? relation_order : order_clause
+      merged_relation = merged_relation.order(merged_order)
+
+      merged_wheres = @relation.wheres
+
+      r.wheres.each do |w|
+        if w.is_a?(Arel::Predicates::Equality)
+          merged_wheres = merged_wheres.reject {|p| p.is_a?(Arel::Predicates::Equality) && p.operand1.name == w.operand1.name }
+        end
+
+        merged_wheres << w
+      end
+
+      merged_relation.where(*merged_wheres)
+    end
+
+    alias :& :merge
+
+  end
+end