Optimize Problem.name to support prefetching #507
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…ject#441) Problem.name previously queried through the whole ProblemName table. Now it accesses the names for the problem through self.names, which allows other code to optimize this query by using prefetch_related on the names property.
Previous implementation of Problem.name errored out if Problem.name was accessed before the instance of Problem was saved with .save(). This is now fixed.
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I changed the implementation of the name property of the Problem model. Now instead of querying the ProblemName table it goes through the names property, which can now be prefetched. This is what I do in task_archive_tag_view which dramatically speeds it up on large competitions, reducing the number of queries from linear in the number of problems to constant.
I also add a test to check that the implementations are consistent.