This removes the `ForkedProjectLink` model that has been replaced by
the `ForkNetworkMember` and `ForkNetwork` combination. All existing
relations have been adjusted to use these new models.
The `forked_project_link` table has been dropped.
The "Forks" count on the admin dashboard has been updated to count all
`ForkNetworkMember` rows and deduct the number of `ForkNetwork`
rows. This is because now the "root-project" of a fork network also
has a `ForkNetworkMember` row. This count could become inaccurate when
the root of a fork network is deleted.
The problem would occur when the `ForkedProjectLink` was deleted, but
the `ForkNetworkMember` was not. The delete would be rolled back and
retried.
But the error would not be saved because `Project#forked?`
would still be true, because the `ForkNetworkMember` exists. But the
`Project#forked_project_link` would be `nil`. So the validation for
the visibility level would fail.
The number of forks of a project doesn't change very frequently and
running a COUNT(*) every time this information is requested can be quite
expensive. We also end up running such a COUNT(*) query at least twice
on the homepage of a project.
By caching this data and refreshing it when necessary we can reduce
project homepage loading times by around 60 milliseconds (based on the
timings of https://gitlab.com/gitlab-org/gitlab-ce).
Bob Van Landuyt