types: improve typing for transform option to toJSON and toObject

[vkarpov15]

Fix #15479

Summary

Better typing for the transform() function, 2nd arg should be a raw doc type by default not Record<string, any>.

Maybe worthwhile to postpone this for a minor release, WDYT @hasezoey ?

Examples

[Copilot]

Pull Request Overview

Adds a type-level test to verify that the transform callback on toJSON receives the correct raw document type and enforces proper return typing.

• Introduces a new test function gh15479 to cover transform option typing
• Defines a transform callback with doc and ret parameters and uses toJSON generics
• Verifies that the returned object omits testField when using the transformed return type

Comments suppressed due to low confidence (1)

test/types/schema.test.ts:1816

• [nitpick] The test function name gh15479 is not descriptive. Consider renaming it to something like testTransformOptionTyping or using Jest's test/it syntax with a descriptive title.

function gh15479() {

[hasezoey]

LGTM, works with typegoose in its current state. Though because it modifies something likely used, i would agree to postpone it to a minor release.

[Sainan]

What's the point of a transform hook if it does not allow transformations :|

[vkarpov15]

@Sainan unfortunate limitation of TypeScript. You can replace delete returnedObject._id; delete returnedObject.__v; with const { _id, __v, ...filteredObject } = returnedObject; return filteredObject; or something similar. The key point is that you can also return the transformed object.

[Sainan]

Well, the client object differs in more than just lacking some fields, some are transformed to different representations. Certainly quite a breaking change and will need to refactor a lot now.

[vkarpov15]

I'm sorry for the inconvenience, this is certainly one of those cases where the line between bug fix and breaking change is blurry. However, I think returnedObject getting typed as any qualifies more as a bug than anything.

[Sainan]

Well, technically it was Record<string, any>, but yeah, I just updated existing transform hooks to specify this as the expected type for returnedObject and that seems to work with Mongoose versions from before and after.