Fix unique constraints for images

[zephraph]

Fixes #2895

As @davepacheco pointed out in #2895, CRDB doesn't treat null as unique which ultimately means duplicate entries can be present. To prevent that I've broken down the constraint down into two indices to ensure the unique constraint is enforced.

[david-crespo]

Great news if that's all it takes.

[david-crespo]

Looks great assuming you confirmed the test fails without the index change.

[zephraph]

Yeah, the only issue is that when the constraint check fails it's a 500 which is not what we want. Need to add some logic around catching that.

[davepacheco]

That's usually a case where something wants to be using ErrorHandler::Conflict instead of some other variant. (Sorry if this is unhelpful -- I haven't looked at the code here.)

[zephraph]

Yeah, that was my conclusion. Unfortunately there's a slight hiccup in that Conflict is mostly used in cases where we have the name in question. In this particular case we don't actually have the name on hand. We're promoting an image by ID and the uniqueness constraint is failing on name. That may mean we need to do a secondary lookup for the name of the resource before doing the insert?

[zephraph]

As an update on this

I paid with @davepacheco and he helped me with some query execution analysis. The query to list a project's images combined with silo images (which is used for situations like instance create) ends up doing a full table scan. We were able to avoid the full table scan by breaking it down into two select queries with a UNION clause combining the results. Diesel exposes capacities for performing a union but I've been struggling to figure out how to slot that in with our current paginated approach.

[zephraph]

I've decided to sidestep the whole issue with the query and just remove the include_silo_images flag when listing project images. It reduces the option space for the UI, but we can always look to add it again later if it's a customer requested feature.

[david-crespo]

So how do you get a list of silo images?

[zephraph]

The images list endpoint already had to modes. /v1/images gives you the silo images. /v1/images?project=:project gives you a project's images. The flag that I removed was /v1/images?project=:project&include_silo_images which allowed for listing both a single projects images alongside all the silo images. The use case there was so that we could have a single image selection interface.

[david-crespo]

Oh right. I forgot about selecting with no param. So the console will just make two requests. No problem.