Add a way to update an entity inside an Entities object

[a0js]

Category

User level API features/changes

Describe the feature you'd like to request

Right now there is no way to update an entity inside an Entities object. For instance, if in my app, a user was assigned to a user group (a parent relation in cedar world), I'd like to be able to set an individual entity and have the relations updated:

let entities = Entities::from_entities(entities_from_db, schema)?;

// update
let update_or_insert_operation = entities.set(entity, schema)?;

// OR
entities.add_entities([entity], schema); // overwrite rather than error on duplicate.

Describe alternatives you've considered

This is what I'm doing currently:

let mut new_entities: Vec<_> = entities
        .iter()
        .filter(|cur_entity| entity.uid() != cur_entity.uid())
        .cloned()
        .collect();

new_entities.push(entity);
entities = Entities::from_entities(new_entities.into_iter(), schema)?;

It just seems unnecessary to clone the entire entities object, just to update one entity, though I am unfamiliar with the deeper workings of the cedar_policy_core module.

Additional context

No response

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

[a0js]

I did see that remove_entities() is getting added, which looks great. But I don't want to use that either as I'd be recalculating the graph relations on remove and add. Looking at some of the internal code, I wonder if this can be accomplished by adding an overwrite boolean option to the add_entities() function which would be forwarded all the way down to the update_entity_map() or maybe adding an upsert_entities() function that would call the internal functions with that boolean flag, so the add_entities doesn't introduce a breaking change.

Another option I see is, adding an upsert_entities() function that runs the remove_entities() first with tc_computation set to AssumeAlreadyComputed, and then run the add_entities() as normal:

// api.rs

    pub fn upsert_entities(
        self,
        entities: impl IntoIterator<Item = Entity>,
        schema: Option<&Schema>,
    ) -> Result<Self, EntitiesError> {
        let entities: Vec<_> = entities.into_iter().collect();
    
        let removed = self.0.remove_entities(
            entities.iter().map(|e| e.uid().0),
            cedar_policy_core::entities::TCComputation::AssumeAlreadyComputed
        )?;
    
        Ok(Self(
            removed.add_entities(
                entities.into_iter().map(|e| Arc::new(e.0)), 
                schema.map(|s| cedar_policy_validator::CoreSchema::new(&s.0))
                    .as_ref(),
                cedar_policy_core::entities::TCComputation::ComputeNow,
                Extensions::all_available(),
            )?
        ))
    }