Adding to Facades

If you do encounter the need to implement custom selectors, it is highly recommended that you integrate them into your entity facades, rather than consume them directly from components. This does of course assume you are using entity facades, and if you have foregone the use of facades then you may use custom selectors as you normally do with @ngrx.

Property or Accessor Method

After creating a custom selector, you will need to determine whether a property or accessor method is appropriate for this new selector in your facade. For non-parameterized selectors, a property is usually most appropriate.

For parameterized selectors, an accessor method may be more appropriate. If however the possible range of input to your parameters is limited then multiple properties that each encompass a particular use case might still be the best option.

Adding a Custom Property

Continuing on with our firstCustomer selector from the previous section, adding this to a CustomerFacade should be very strait forward:

import {firstCustomer, CustomerFacadeBase} from 'state/customer.state';
import {Customer} from 'models';

export class CustomerFacade extends CustomerFacadeBase {
    constructor(store: Store<AppState>) {
        super(Customer, store);
    }
    
    get firstCustomer$(): Observable<Customer> {
        return this.store.pipe(select(firstCustomer));
    }
}

Adding a Custom Accessor Method

With a parameterized selector like our prior customerById example, we should use a method instead of a property to allow passing in the id of the customer to select:

import {firstCustomer, customerByName, CustomerFacadeBase} from 'state/customer.state';
import {Customer} from 'models';

export class CustomerFacade extends CustomerFacadeBase {
    constructor(store: Store<AppState>) {
        super(Customer, store);
    }
    
    get firstCustomer$(): Observable<Customer> {
        return this.store.pipe(select(firstCustomer));
    }
    
    customerByName$(name: string): Observable<Customer> {
        return this.store.pipe(select(customerByName, {name});
    }
}