Add a class for backend compatibility

[parsonsmatt]

This PR will enable Esqueleto queries to be used by the persistent-typed-db library, along with other database backends.

This is a WIP, please don't merge until I've had time to use it in-anger.

[parsonsmatt]

This PR now uses the backend compatibility class introduced in persistent-2.7.1 instead of defining it here.

The work project "just worked" with this patch and the new persistent, so I suspect it's fine. I'll try to find someone with heavier usage of the SqlReadT stuff to see if it is OK for them.

[parsonsmatt]

I've opened this PR in persistent that should make this a non-breaking change for existing projects. Once that's reviewed/merged, I'll bump the lower bounds on this library, use the hackage version, and we'll be in business :)

[dariooddenino]

Using both this PR and the persistent one you linked, I still get this error:

 • No instance for (BackendCompatible SqlBackend (SqlFor LivDB))
        arising from a use of ‘E.select’
    • In a stmt of a 'do' block:
        E.select
        $ E.from
          $ \ p
              -> do { E.where_ (p E.^. Wp_postmetaMeta_id E.==. E.val x);
                      return p }
      In the second argument of ‘($)’, namely
        ‘do { E.select $ E.from $ \ p -> do { ... } }’
      In the expression:
        runLiv $ do { E.select $ E.from $ \ p -> do { ... } }

Persistent queries work correctly. It's a mysql db on persistent-mysql-2.7.1

[parsonsmatt]

@dariooddenino Try with latest commit of persitent-typed-db -- I forgot to move the instance into the library :)

[dariooddenino]

persistent-typed-db last commit fixed this :)

Just a note: valkey still uses toSqlKey instead of toSqlKeyFor

[dariooddenino]

Does this works for select only? If I try to use update I get the Couldn't match type 'SqlFor Foo' with 'SqlBackend' error.
Let me know if you need more info :)

[parsonsmatt]

@dariooddenino I have added tests for the persistent-typed-db library that ensure that it type checks with updates and selects now :)

@bitemyapp This is working and relying on Hackage persistent. However, upstream persistent bundles along new Conduit and a bunch of other breaking changes. Merging and releasing this would be a major bump probably. Thoughts?

[bitemyapp]

@parsonsmatt I lean towards doing major bumps whenever in doubt. I will have time this weekend to help with this too.

[parsonsmatt]

Cool. If you're good with a major bump for this, then Im happy with that too. Anything we want to get in with this version?

[bitemyapp]

@parsonsmatt other than any relevant persistent and conduit upgrades? Not that I'm aware of off-hand but I'll re-peruse the diff and be more certain after I've done so. You got anything in mind?

[parsonsmatt]

Idk, there's probably some deprecations or stuff that can make the interface better?

[bitemyapp]

@parsonsmatt I have some work to do yet on cleaning up the test suite but this is now merged. Thank you very much!