Support Table Foreign Key Constraints in SQLite

[kderme]

This pr adds support for foreign keys, table constraints in SQLite. They can only reference Primary keys of other tables and not Unique keys, since this would require changes in Quasi and I'm not sure how well this is supported in other dbs. I've tested migrations from existing schemas, which adds new foreign keys to existing Tables and it also works fine.

Before submitting your PR, check that you've:

• Bumped the version number
• Documented new APIs with Haddock markup
• Added @since declarations to the Haddock

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[parsonsmatt]

Code looks good to me.

They can only reference Primary keys of other tables and not Unique keys, since this would require changes in Quasi and I'm not sure how well this is supported in other dbs.

Can you elaborate?

[kderme]

Sure! What I mean is that this migration works fine with this pr

share [mkPersist sqlSettings, mkSave "entityDefs"] [persistLowerCase|
Person
    name String
    lastNameId Int
    Primary name lastNameId
    deriving Eq Show

Car
   owner String
   ownerId Int
   color String
   Foreign Person belongs owner ownerId
|] 

but this

share [mkPersist sqlSettings, mkSave "entityDefs"] [persistLowerCase|
Person
    name String
    lastNameId Int
    UniquePerson name lastNameId
    deriving Eq Show

Car
   owner String
   ownerId Int
   color String
   Foreign Person belongs owner ownerId
|]

still fails with

     • Exception when trying to run compile-time code:
        no explicit primary key fdef=ForeignDef ...

Such a migration is accepted by SQLite (actually now that I checked again, SQLites accepts it even without the unique constraint).

[parsonsmatt]

Right, thanks. I'm good to accept and merge this as-is then if you want to bump the relevant version numbers and add a changelog entry 😄

[parsonsmatt]

CI is passing, merging and releasing. Thanks!