Building Your Entity States

Initialization Simplified

At the core of NgRx Auto-Entity is the buildState function. This utility function encapsulates the creation and management of all the "boilerplate" that you would normally implement yourself when building up state for a new entity. In the past you may have manually created an @ngrx/entity adapter, built out your standardized reducer function, and exported a bunch of support elements like initial state, selectors, a key selection handler, etc.

Just "buildState()!"

Now you simply need to call buildState() like so:

entity.state.ts

import { IEntityState } from '@briebug/ngrx-auto-entity';
import { Model } from 'models';

const { initialState } = buildState(Model);
export function entityReducer(state = initialState): IEntityState<Model> {
    return state;
}

That is about as simple as it gets, unless you need to do anything custom, such as add your own additional support actions, use selectors, or retrieve the prefabricated facade base class so you can keep your state encapsulated.

Rich Functionality

The buildState function provides all of the functionality necessary to take control when you need to, without being complex, and all while still handling most of the work for you. The full expression of a buildState call would be as follows:

import { IEntityState } from '@briebug/ngrx-auto-entity';
import { Model } from 'models';

export const { 
    initialState, 
    selectors: {
        selectAll: allModels,
        selectEntities: modelEntities,
        selectIds: modelIds,
        selectTotal: countOfModels,
        // Additional selectors...
    }, 
    entityState, 
    facade: ModelBaseFacade,
    reducer: modelReducer // Sadly, this does not work with AOT! :'(
} = buildState(Model);

// Extracted projection for easier unit testing
export const findFirstModel = (state: IEntityState<Model>) => 
    (entityState.ids?.length && entityState.entities) 
      ? entityState.entities[entityState.ids[0]] 
      : null;

// Selectors are simply compositions of other selectors and a projection
export const firstModel = createSelector(
    entityState,
    findFirstModel
);

In addition to providing the initial state version for your stub reducer, the buildState() function also provides a selectors map, an entityState selector to support the creation of custom selectors, a base facade class (source of ultimate power and simplicity!), and finally a ready-made stub reducer (only works with non-AOT builds, sorry!)