commit 67d33d9680a49858d2033a7eec40c9be50db80ae
author Sean Griffin <sean@seantheprogrammer.com> Wed Oct 03 12:23:19 2018 -0600
committer Sean Griffin <sean@seantheprogrammer.com> Wed Oct 03 13:22:37 2018 -0600
tree f34161190260408bbb531803092f5f11e4db5951
parent db66040008c7e951e1be74a199a309e9142d175f

Support `diesel_manage_updated_at` on SQLite

There's a little bit of funkiness required to make this work. The first
piece is that we need to modify the function registration to provide
access to the connection for our internal functions. This isn't
*strictly* necessary, we could `transmute` the `&self` to be `&'static
self`, since the function will never be called after `self` is dropped.
That felt like it would add some unneccessary unsafety though.

The second bit of funkiness is that we have to have *some* return type,
so we can't just return `()`. I think I want to fix this in the future
by providing a `Null` SQL type, which provides `ToSql` and `FromSql`
impls only for `()`. This requires adding a variant to `SqliteType` and
`MysqlType` though, so it will have to be done in 2.0.

The function itself is subtly different from the PostgreSQL version,
since it runs even if no values were actually changed (we can't do
something like `NEW IS DISTINCT FROM OLD` here). This also cannot be run
on tables without ROWIDs. I think we should probably declare this as a
SQL function in code somewhere for documentation purposes, but I want to
wait until our docs are building again to follow up with that.