Posts and PrivatePosts should be ordered by created_at not by id

[timdiggins]

Currently posts & private posts when order_oldest_first / order_newest_first are actually (under the hood) ordered by id.

This seems appealing in some ways, but it is a bit of a nightmare. In particular if the creation order is screwed up (e.g. by importing) then you have problems. It also just feels wrong to me -- and it was deeply surprising when I found out.

I have started changing this behaviour to be ordered by created_at

Of course changing this is quite a bit of work, as much test data currently relies on this, and some untested behaviours (e.g. Post / PrivatePost #page())

However, I've also discovered that there are one or two places where some desired behaviours rely on a natural id-ordering (rather than explicit call to order_oldest_first) which is not dependable (at least in postgres).

• change ordering
• deal with spec failures (including the read-state spec mentioned in Sporadic spec failure in travis ci #352)
• add in default order_oldest_first for the associations in Topic and PrivateTopic
• write spec for and change #page for both Post and PrivatePost
• dry up #page by extracting to either PostCommon or PageCalculable

[timdiggins]

FYI: Having looked through the usages of .posts, none are actually reordering the posts, and many are relying on the id-order. I think we should change the default order of the associations (not the model) to be order_oldest_first. this can be overridden with .reorder(). This may be a controversial choice!

[glebm]

👍

Default order on associations is probably OK, though I'd prefer no default order on them at all.

[timdiggins]

@glebm I get your reluctance for lack of default order, but it seemed a bit repititive to add the order to every single place we are using .posts...