Enforce integrity constraints for module links

[cortopy]

According to the docs:

By default, the defined link establishes a one-to-one relation: a record of a data model is linked to one record of the other data model.

If a one-to-many relation is desired, then the isList option can be declared to represent that in the schema.

However, that option doesn't do anything apart from changing the way in which typescript types are generated. There are many unexpected behaviours.

Unexpected behaviours

Creation of links doesn't guarantee data consistency

Even if isList: false is specified (default), doing the following will create two links:

export default defineLink(
  ProductModule.linkable.product,
  HelloModule.linkable.myCustom
)

await link.create({
  [Modules.PRODUCT]: {
    product_id: "prod_123",
  },
  "helloModuleService": {
    my_custom_id: "mc_123",
  },
})

await link.create({
  [Modules.PRODUCT]: {
    product_id: "prod_456",
  },
  "helloModuleService": {
    my_custom_id: "mc_123",
  },
})

This really caught me out, as I thought that there would some kind of integrity constraints in postgres that would stop applications from creating more than one link if a relationship is one-to-one. The database is a RDBS after all, and this is totally unexpected.

Typescript types are not safe

Because isList is false, type are only generated "as if" the response from the query is guaranteed to never be an array, but this isn't true, since a query will return an array if there's more than one.

Query doesn't work as expected

According to the docs on query,

If the linked data model has isList enabled in the link definition, pass in fields the data model's plural name suffixed with .*.

But it seems that me that this is cosmetic and doesn't really represent any schema constraints. If there is more than one link as per the example above, querying using the singular would still return an array.

Feature request

I would have thought that following applies:

• link.create throws an error if the link already exists or if either entity is already linked to a different record.
• Typescript types are safe and the singular and plurals are guaranteed to match between types and runtime behaviours.
• In a one-to-one relation, a query with a plural name would always return undefined if there is one link. Likewise, a one-to-many would return undefined if queries in the singular form.

[olivermrbl]

Hey @cortopy, appreciate the feedback.

These are all great feature requests–some were already on our radar. We expect to look into adding these soon.

[cortopy]

thanks so much @olivermrbl ! Hearing that it's on your radar makes me very happy.

I'd assume that there would more than one way to achieve this and a solution design would be required. I'd be very glad to contribute to either ideation or some kind of PR