feat: add OperationHookContext interface

[hacksparrow]

Added typings for supporting operation hooks in LB4. Part of addressing loopbackio/loopback-next#3952.

Signed-off-by: Hage Yaapa hage.yaapa@in.ibm.com

Checklist

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• New tests added or existing tests modified to cover all changes
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[bajtos]

Good start, I have few comments to discuss.

[agnes512]

Can we have API docs, example, r comments on what this new interface is for? Same for the rest of changes.

[hacksparrow]

Added.

[bajtos]

The changes LGTM as an incremental improvement.

However, I am not sure if they are actually addressing the needs of loopbackio/loopback-next#4730?

As I understand the big picture, the problem is not in the fact that we don't have typings for observe(), the current typings should be good enough (even if not as flexible and easy to use as we would like to). What we are missing is the information that every PersistedModel includes ObserverMixin. In fact, Model classes provide Observer functionality too:

https://github.com/strongloop/loopback-datasource-juggler/blob/36303b3b63932478cb429b5c5af6fec7f09b602c/lib/model.js#L868-L869

I think the missing piece is how to tell that information to TypeScript. Ideally, we want to say:

• if a class T extends Model, then it will include ObserverMixin<T> methods

I am not sure if TypeScript makes this possible. If not, then I am fine to use a slightly less useful variant:

• Model implements ObserverMixin<Model>
• PersistedModel implements ObserverMixin<PersistedModel>

(I consider this a slightly less useful because hooks will have access to PersistedModel APIs only, they won't be able to access static methods and properties added by the particular model being observed.)

Since our primary motivation is to allow LB3 developers to migrate their operation hooks to LB4, it may be best to go with the second option and defer better typings to #1822 again.

[bajtos]

Regarding the commit message:

chore: typings for supporting operation hooks in LB4

Commit type chore is used for changes that are not affecting users. The changelog generator we use in loopback-next is excluding such commits from the log.

Since you are improving type definitions, you should use feat type.

[hacksparrow]

Will edit in the final commit message after squashing the commits.