Disable ONLY_FULL_GROUP_BY mode for mysqlrails5-mysql-group-by

* disables ONLY_FULL_GROUP_BY option which is enabled by default in
rails 5
* reverts 'uniq' workaround which was necessary only when this option
was enabled

1 files changed, 29 insertions, 0 deletions

diff --git a/lib/mysql_session_options.rb b/lib/mysql_session_options.rb
new file mode 100644
index 00000000000..9ba1e508218
--- /dev/null
+++ b/lib/mysql_session_options.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'active_record/connection_adapters/abstract_mysql_adapter'
+
+module MysqlSessionOptions
+  def configure_connection
+    super
+
+    # Disable NO_ZERO_DATE mode for mysql.
+    # We use zero date as a default value
+    # (config/initializers/active_record_mysql_timestamp.rb), in
+    # Rails 5 using zero date fails by default (https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/75450216)
+    # and NO_ZERO_DATE has to be explicitly disabled. Disabling strict mode
+    # is not sufficient.
+    sql_mode = "REPLACE(@@sql_mode, 'NO_ZERO_DATE', '')"
+
+    # Disable ONLY_FULL_GROUP_BY for mysql.
+    # If ONLY_FULL_GROUP_BY is enabled then GROUP BY clause
+    # must include all columns used in SELECT, HAVING and ORDER BY.
+    # This causes that "duplicit" records are then returned in
+    # some of our queries and these have to be filtered-out
+    # on rails side.
+    sql_mode = "REPLACE(#{sql_mode}, 'ONLY_FULL_GROUP_BY', '')"
+
+    @connection.query "SET @@SESSION.sql_mode = #{sql_mode};" # rubocop:disable Gitlab/ModuleWithInstanceVariables
+  end
+end
+
+ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter.prepend(MysqlSessionOptions) if Gitlab.rails5?