NgRx Selectors

Selectors are pure functions used for obtaining slices of store state.

Selector by route

This will select based on route data, example: /invoice/123

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--- foo.facade.ts
public getCurrentInvoice (): Observable<IStoreItem<IInvoice>> {
    return this._store.select(InvoiceSelectors.byRoute).pipe(
        // tap(a => console.log(a)),
        filter(a => a.isLoading === false),
        dispatchAndSelect(
            invoice => this._store.dispatch(new GetInvoiceAction(invoice)),
            this._store.select(InvoiceSelectors.currentInvoice)
        )
    );
}

--- foo.selectors.ts
export const byRoute = createSelector(
	RouterSelectors.currentParams,
	(params: Params): string => {
		return params.id;
	}
);

export const currentInvoice = createSelector(
  selectFeature,
  (state: FeatureState) => state.counter
);

IStoreItem is just a way to wrap the response and universally (thought-out your application) check if the store slice ready.

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export interface IStoreItem<T> {
    isLoading: boolean;
    item?: T;
}

Using selectors with props

To select a piece of state based on data that isn’t available in the store you can pass props to the selector function. 

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--- foo.facade.ts
public getCurrentInvoice (): Observable<IStoreItem<IInvoice>> {
  return this._store.pipe(select(fromRoot.getCount, { multiply: 2 }))
}

--- foo.selectors.ts
--- here `counter` is the response from `getCounterValue` and `props` came from the call to `getCount` above. NgRx is wierd :D

export const getCount = createSelector(
  getCounterValue,
  (counter, props) => counter * props.multiply
);

Jest

Jest is a javaScript testing framework.

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toHaveBeenCalledWith

toBeInstanceOf

toBe

toMatchSnapshot

TestBed with mockReturnValue

This can be called inside the tests body to mock out the function getFeatures

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TestBed.get(SomeFacade).getFeatures = jest.fn().mockReturnValue(of());

Data driven

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--- with toBeObservable
describe('[childComponentEnabled$]', () => {
    [
        { abName: true, expected: true },
        { abName: false, expected: false }
    ].forEach(({ abName, expected }) =>
        it(`should ${expected ? '' : 'not'} use 'child-component-to-maybe-show' if abName feature is ${abName}`, marbles((m) => {
            // Arrange
            const fixture = TestBed.createComponent(ParentComponent);
            const testComponent = fixture.componentInstance;
            const abFeature = <IAbFeature> {
                name: 'abName',
                value: abName.toString(),
                winningVariantName: 'OnVariant'
            };
            TestBed.get(AbFrameworkFacade).getByName = () => of(abFeature);

            // Act
            fixture.detectChanges();

            // Assert
            m.expect(testComponent.childComponentEnabled$).toBeObservable('(a|)', {
                a: expected
            });
        }))
    );
});

--- passing the array elements by object `testcase`
describe(`getSomeMethod`, () => {
    [
        {
            someObject: {},
            someBool: true,
            someString: 'hoe',
            someEnum: SomeEnum.hoe,
            expected: 'foo'
        },
        {
            someObject: {},
            someBool: true,
            someString: 'bazz',
            someEnum: SomeEnum.foo,
            expected: 'foo bar'
        }
    ].forEach(testcase => {
        it(`does some sweet thing,
        testcase ${JSON.stringify(testcase)}`, () => {
			// do all the things and set `actual`
			const actual = 'wat';
            expect(actual).toBe(testcase.expected);
        });
    });
});

References

Raspberry Pi Cluster

Docker Swarm

Python Example

Sweet python script example to warm the Pi’s CPU!

References