Feature request: Methods in enforcer for adding, updating and deleting policies without usage of adapter (even if autoSave is true)

[yiev]

My environment/setup:

• Microservice architecture
• using casbin with casbin-mongoose-adapter (SyncedAdapter) and @casbin/mongo-changestream-watcher
• autoSave is true

For my use case I need methods in the enforcer for adding, updating and deleting policies only inside the enforcer object itself - even if an adapter is set and autoSave is true.

I need these functions, to be able to call them in the updateCallback of the watcher of all microservices, because I need the watcher to keep the policy up to date across all microservices. With the currently available methods its not possible to do this without any performance issues or creating duplicates of policies in the MongoDB collection.

This issue results out of a PR (#505) for discussion.

The methods, that I added, are for me for calling inside the updateCallback() of the watcher.

Here is a detailed example to better understand my problem:

Lets say we got three microservices (A, B and C), all three can interact with the casbin policy (reading, adding, updating, deleting policies).

Microservice A adds a new policy via enforcer.addPolicy(). This leads to a new document in the MongoDB collection and that creates a change event on the MongoDB change stream.

So the updateCallback function of the watcher in all three microservices is called. In this function I could just reload the whole policy via enforcer.loadPolicy(). This would work! BUT that is performance wise a bad idea if we got severval hundred microservices doing that all the time.
So in the updateCallback function of all three microservices I check instead first:

• is the newly added policy already part of the policy of the enforcer?
  • in microservice A it is already part of the policy, so we don't do anything further
  • in microservice B and C the newly added policy is not part of the policy:
    • I call enforcer.addPolicy() to add it to the policy of the enforcer of microservice B and C. But enforcer.addPolicy() also adds the policy via the adapter by calling adapter.addPolicy(). So at this point I am creating duplicates of the new policy in the MongoDB colleciton. And enforcer.addPolicy() also calls the watcher.update() again which is just unnecessary but causing no issues.

So I wanted a method for adding policies, that does not call adapter.addPolicy() and also does not call watcher.update(). The same for updating and deleting policies. So what I need are functions like selfAddPolicy(), selfRemovePolicy(), and so on that not only don't call watcher.update() but also don't call the adapter functions on policy changes.

I hope it makes sense, why I want these new methods? Or am I missing something and my approach does not make any sense?

[DropzRain]

Hi, thanks for the great work!
I was facing a similar issue with typeorm-adapter and Mongo changestream watching some time ago. I implemented custom internal methods to handle it but would welcome a proper solution :)