Merge branch 'atom-feed-latest-update' into 'master'

Improve performance of user profiles, finding groups, and finding projects

This MR improves the following:

* Rendering of profile pages and Atom feeds
* Finding groups (using GroupsFinder & friends)
* Finding projects (using ProjectsFinder & friends)

Initially this MR was intended to only improve rendering of Atom feeds, but over time other fixes were introduced as well as the same code was the cause of all these problems.

See merge request !1790

1 files changed, 34 insertions, 0 deletions

diff --git a/lib/gitlab/sql/union.rb b/lib/gitlab/sql/union.rb
new file mode 100644
index 00000000000..1cd89b3a9c4
--- /dev/null
+++ b/lib/gitlab/sql/union.rb
@@ -0,0 +1,34 @@
+module Gitlab
+  module SQL
+    # Class for building SQL UNION statements.
+    #
+    # ORDER BYs are dropped from the relations as the final sort order is not
+    # guaranteed any way.
+    #
+    # Example usage:
+    #
+    #     union = Gitlab::SQL::Union.new(user.personal_projects, user.projects)
+    #     sql   = union.to_sql
+    #
+    #     Project.where("id IN (#{sql})")
+    class Union
+      def initialize(relations)
+        @relations = relations
+      end
+
+      def to_sql
+        # Some relations may include placeholders for prepared statements, these
+        # aren't incremented properly when joining relations together this way.
+        # By using "unprepared_statements" we remove the usage of placeholders
+        # (thus fixing this problem), at a slight performance cost.
+        fragments = ActiveRecord::Base.connection.unprepared_statement do
+          @relations.map do |rel|
+            rel.reorder(nil).to_sql
+          end
+        end
+
+        fragments.join("\nUNION\n")
+      end
+    end
+  end
+end