This commit adds the module `FromUnion`, which provides the class method
`from_union`. This simplifies the process of selecting data from the
result of a UNION, and reduces the likelihood of making mistakes. As a
result, instead of this:
union = Gitlab::SQL::Union.new([foo, bar])
Foo.from("(#{union.to_sql}) #{Foo.table_name}")
We can now write this instead:
Foo.from_union([foo, bar])
This commit also includes some changes to make this new setup work
properly. For example, a bug in Rails 4
(https://github.com/rails/rails/issues/24193) would break the use of
`from("sub-query-here").includes(:relation)` in certain cases. There was
also a CI query which appeared to repeat a lot of conditions from an
outer query on an inner query, which isn't necessary.
Finally, we include a RuboCop cop to ensure developers use this new
module, instead of using Gitlab::SQL::Union directly.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/51307
This notifies developers when calling `find(_by!)` chained on
`execute`. And suggests using the methods from `FinderMethods`. These
will perform the correct authorization checks on the resource when it
is found.
This reverts the addition of the "goldiloader" Gem and all use of it.
While this Gem is very promising it's causing a variety of problems on
GitLab.com due to it eager-loading too much data in places where we
don't expect/can handle this. At least for the time being this means we
have to go back to manually fixing N+1 query problems, but at least
those should not cause a negative impact on availability.
