Using selectors with ngrx data - ngrx

Question

how can we use memoization capabilty of selectors using ngrx data with their capabality?
How to create selectors from ngrx data "entityCache" state inside store?
Thank you

Answer 1

Can you clarify what kind of selector you are looking for? The EntityCollectionService has a bunch of preset selectors, though the documentation is not extensive. Here is a list of the "built-in" selectors per the source code.
/** Observable of the collection as a whole */
readonly collection$: Observable<EntityCollection> | Store<EntityCollection>;
/** Observable of count of entities in the cached collection. */
readonly count$: Observable<number> | Store<number>;
/** Observable of all entities in the cached collection. */
readonly entities$: Observable<T[]> | Store<T[]>;
/** Observable of actions related to this entity type. */
readonly entityActions$: Observable<EntityAction>;
/** Observable of the map of entity keys to entities */
readonly entityMap$: Observable<Dictionary<T>> | Store<Dictionary<T>>;
/** Observable of error actions related to this entity type. */
readonly errors$: Observable<EntityAction>;
/** Observable of the filter pattern applied by the entity collection's filter function */
readonly filter$: Observable<string> | Store<string>;
/** Observable of entities in the cached collection that pass the filter function */
readonly filteredEntities$: Observable<T[]> | Store<T[]>;
/** Observable of the keys of the cached collection, in the collection's native sort order */
readonly keys$: Observable<string[] | number[]> | Store<string[] | number[]>;
/** Observable true when the collection has been loaded */
readonly loaded$: Observable<boolean> | Store<boolean>;
/** Observable true when a multi-entity query command is in progress. */
readonly loading$: Observable<boolean> | Store<boolean>;
/** ChangeState (including original values) of entities with unsaved changes */
readonly changeState$:
| Observable<ChangeStateMap<T>>
| Store<ChangeStateMap<T>>;

Answer 2

For me at the beginning was a little bit confusing as well. The selectors are used behind a Facade Pattern.
Have a look at this article https://medium.com/#thomasburlesonIA/ngrx-facades-better-state-management-82a04b9a1e39, it may help you for having a better understanding.
ngrx/data uses by default that pattern (that's not ngrx, although you can create your own facade as in the article is explained).
Summarizing
----------------- ngrx -----------------
----------------- ngrx/data -----------------
you can find more in https://ngrx.io/guide/data/architecture-overview
...
Your component also subscribes to one or more of the service's Observable selectors in order to reactively process and display entity state changes produced by those commands.
...
However, again from documentation seems very confuse...
Have a look to this picture
from https://slides.com/jiali/deck-5#/14, good read either.
In this last picture as #bkelley said, you can use EntityCollectionService, it is the Facade in ngrx/data
Hope this help