DatX data store
Last modified on Thu 07 Oct 2021

This chapter covers setup and use DatX data store within Angular project and how to use it in tests. If you are not familiar with it yet, resources below can help.

Resources

You can read up on DatX at the official docs site. Infinum also published the working with JSON API article with examples. We also have an example repository that you can take a look at when in doubt about how to set up DatX in an Angular project.

Why use DatX

Apart from providing possible single source of truth for any shared data with a basic querying and referencing support, it also provides options to extend any entity with mixins such as withActions, withMeta, withPatches, which enhance entities with usefull utility functions, or network related ones like withNetwork, jsonapi or, useful in Angular's case, jsonapiAngular. Especially with jsonapi and/or jsonapiAngular, interacting with JSONAPI standard compliat backend can be much easier then building requests manually and more managable than building API related code with some sort of generator.

Setup

Let's start by installing all DatX related dependencies we will need:

npm i --save @datx/core @datx/jsonapi @datx/jsonapi-angular

Since we didn't include mobx (because it doesn't play nice with RxJS), we need to add a little boilerplate to work around that. First we need to instruct DatX not to use mobx, by adding '@datx/core/disable-mobx' before App bootstrap:

// src/main.js AND src/test.js
import '@datx/core/disable-mobx';

Next, we need to overwrite mobx path so that it can be resolved by datx, albeit to an empty file:

// /tsconfig.json
{
    ...
    "compilerOptions": {
        ...
        "paths": {
            ...
            "mobx": ["./mobx.js"]
        }
    }
}

Lastly, we bypass @datx/core/disable-mobx related import warning by adding its non ECMAScript module dependency to a whitelist:

// angular.json
{
    ...
    "architect": {
        ...
        "build": {
            ...
            "options": {
                ...
                "allowedCommonJsDependencies": ["@datx/utils"],
            }
        }
    }
}

Defining models and their relationships

This topic is heavily described in the resources above, please refer to them. By convention, you can put all models in src/app/models directory and collections to src/app/collections of your Angular project. Once you are finished describing all Resource Objects you can move to the next section, just remember that you will most likely want to use jsonapiAngular so that you can work with observables when calling async methods on models.

Store setup and injection

To create and provide a single instance of Collection accross entire Angular app, you can create custom DI token eg. APP_COLLECTION, see InjectionToken docs and then provide said token in root module, like so:

// injection-tokens.ts
import { InjectionToken } from '@angular/core';
import { AppCollection } from '<path-to-collection-definition>';

export const APP_COLLECTION = new InjectionToken<AppCollection>(
  'APP_COLLECTION'
);
// app.module.ts
import { APP_COLLECTION } from '<path-to-token-definition>';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { AppCollection } from '<path-to-collection-definition>';

@NgModule({
    declarations: [AppComponent],
    imports: [
        ...
    ],
    providers: [
    ...
    {
      provide: APP_COLLECTION,
      useValue: new AppCollection();
    }
    ...
  ],
  bootstrap: [AppComponent],
}
export class AppModule {}

Whenever you want to work with the collection from within Angular's DI container, you can simply use the token above to inject the collection instance.

// example.service.ts
import { APP_COLLECTION } from '<path-to-token-definition>';
import { Inject, Injectable } from '@angular/core';
import { AppCollection } from '<path-to-collection-definition>';

@Injectable({
  providedIn: 'root',
})
export class ExampleService {
  constructor(
    @Inject(APP_COLLECTION) protected readonly collection: AppCollection // app.module.ts scoped instance of AppCollection
  ) {}
}

When testing consumers of APP_COLLECTION, just inject the collection under the same token again, as with any other dependency:

// example.service.spec.ts
import { AppCollection } from '<path-to-collection-definition>';
import { APP_COLLECTION } from '<path-to-token-definition>';
import { TestBed } from '@angular/core/testing';
import { ExampleService } from './example.service';

describe('ExampleService', () => {
  let service: ExampleService;

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        {
          provide: APP_COLLECTION,
          useValue: new AppCollection(), // empty mock collection
        },
      ],
    });
    service = TestBed.inject(ExampleService);
  });

  it('should be created', () => {
    expect(service).toBeTruthy();
  });
});

Configuring DatX HTTP calls interception

By default, DatX uses Fetch API when invoking HTTP calls, but this means that it also bypasses HttpClient from @angular/common/http and therefore any registered interception logic or similar kind of middleware. Luckily there is a way around that, see official documentation guide.

You might want to abstract away a bit of the tediousness of working with DatX and/or bind some special logic to a given entity. Since many of the Collection's methods require an Entity type as a parameter you can create separate service that will hide this small implementation detail for you. One way to do that would be to extend an abstract class similar to this one:

// collection.service.ts
import { Inject } from '@angular/core';
import { IModelConstructor, IRawModel, IType } from '@datx/core';
import { IRequestOptions } from '@datx/jsonapi';
import { IJsonapiModel, Response } from '@datx/jsonapi-angular';
import { Observable } from 'rxjs';
import { map, mapTo } from 'rxjs/operators';
import { AppCollection } from '<path-to-collection-definition>';
import { APP_COLLECTION } from '<path-to-token-definition>';

export abstract class CollectionService<TModel extends IJsonapiModel> {
  protected abstract readonly ctor: IModelConstructor<TModel>;

  constructor(
    @Inject(APP_COLLECTION) protected readonly collection: AppCollection
  ) {}

  public create(rawModel: IRawModel | Record<string, unknown>): TModel {
    if (
      rawModel.id === null ||
      rawModel.id === undefined ||
      rawModel.id === ''
    ) {
      delete rawModel.id;
    }

    return this.collection.add(rawModel, this.ctor);
  }

  public createAndSave(
    rawModel: IRawModel | Record<string, unknown>
  ): Observable<TModel> {
    const model = this.create(rawModel);
    return this.save(model);
  }

  public findAll(): Array<TModel> {
    return this.collection.findAll<TModel>(this.ctor);
  }

    // *Model(s) suffix methods unpack the Model from what would else be a Response object,
    // this mirrors the default HttpClient behavior where you also don't get Response metadata by default, just the body.

    // get all entities without any sort of filter unless explicitly specified
  public getAllModels(options?: IRequestOptions): Observable<Array<TModel>> {
    return this.getMany(options,
      queryParams: {
        ...options?.queryParams,
        custom: options?.queryParams?.custom || [],
      },
    }).pipe(map(({ data }: Response<TModel>) => data));
  }

  public getMany(options?: IRequestOptions): Observable<Response<TModel>> {
    return this.collection.getMany<TModel>(this.ctor, options);
  }

  public getManyModels(options?: IRequestOptions): Observable<Array<TModel>> {
    return this.getMany(options).pipe(
      map(({ data }: Response<TModel>) => data)
    );
  }

  public getOne(
    id: IType,
    options?: IRequestOptions
  ): Observable<Response<TModel>> {
    return this.collection.getOne(this.ctor, id.toString(), options);
  }

  public findOne(id: IType): TModel | null {
    return this.collection.findOne(this.ctor, id);
  }

  public getOneModel(
    id: IType,
    options?: IRequestOptions
  ): Observable<TModel | null> {
    return this.getOne(id, options).pipe(
      map(({ data }: Response<TModel>) => data)
    );
  }

  public save(model: TModel): Observable<TModel> {
    return model.save().pipe(mapTo(model));
  }

  public removeOne(id: IType): void {
    this.collection.removeOne(this.ctor.type, id);
  }
}

And then just extend said class:

// entity.service.ts
import { Inject, Injectable } from '@angular/core';
import { AppCollection } from '<path-to-collection-definition>';
import { APP_COLLECTION } from '<path-to-token-definition>';
import { Entity } from '<path-to-entity-definition>';
import { CollectionService } from '<path-to-collection-service>';

@Injectable({
  providedIn: 'root',
})
export class EntityService extends CollectionService<Project> {
  protected readonly ctor = Entity;

  constructor(
    @Inject(APP_COLLECTION) protected readonly collection: AppCollection
  ) {
    super(collection);
  }
}

Such service can be injected from within DI container like any other:

// entity-list.component.ts
@Component({
    ...
})
export class EntityListComponent {
    public readonly entities$ = this.entity.getAllModels();

    constructor(private readonly entity: EntityService) {}
}

When testing these abstractions, it advisable to create test doubles that replace any methods that would make API calls with an implementation which works with in memory collection, like in this example CollectionTestingService:

// collection.testing.service.ts
import { HttpErrorResponse } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { IModelConstructor, IRawModel, IType } from '@datx/core';
import { Response, IJsonapiModel } from '@datx/jsonapi-angular';
import { Observable } from 'rxjs';
import { AppCollection } from '<path-to-app-collection>';
import { ExtractPublic } from '<path-to-extract-public-helper>';
import { asyncData, asyncError } from '<path-to-helpers>';
import { CollectionService } from '<path-to-collection-service>';

@Injectable()
export abstract class CollectionTestingService<TModel extends IJsonapiModel>
  implements ExtractPublic<CollectionService<TModel>>
{
  protected abstract ctor: IModelConstructor<TModel>;

  constructor(protected readonly collection: AppCollection) {}

  public setData(
    data: Array<IRawModel | Record<string, unknown>>
  ): Array<TModel> {
    this.collection.removeAll(this.ctor);
    return this.collection.add(data, this.ctor);
  }

  public create(rawModel: IRawModel | Record<string, unknown>): TModel {
    return this.collection.add(rawModel, this.ctor);
  }

  public createAndSave(
    rawModel: IRawModel | Record<string, unknown>
  ): Observable<TModel> {
    const model = this.create(rawModel);
    return this.save(model);
  }

  public findAll(): Array<TModel> {
    return this.collection.findAll(this.ctor);
  }

  public getAllModels(): Observable<Array<TModel>> {
    return asyncData(this.collection.findAll(this.ctor));
  }

  public getMany(): Observable<Response<TModel>> {
    const data = this.collection.findAll(this.ctor);
    return asyncData({
      data,
      meta: { total_count: data.length },
    } as Response<TModel>);
  }

  public getManyModels(): Observable<Array<TModel>> {
    return asyncData(this.collection.findAll(this.ctor));
  }

  public getOne(id: IType): Observable<Response<TModel>> {
    return asyncData({
      data: this.collection.findOne(this.ctor, id),
    } as Response<TModel>);
  }

  public getOneModel(id: IType): Observable<TModel | null> {
    const model = this.collection.findOne(this.ctor, id);
    return model
      ? asyncData(model)
      : asyncError(new HttpErrorResponse({ status: 404 }));
  }

  public findOne(id: IType): TModel | null {
    return this.collection.findOne(this.ctor, id);
  }

  public save(model: TModel): Observable<TModel> {
    return asyncData(model);
  }

  public removeOne(id: IType): void {
    this.collection.removeOne(this.ctor.type, id);
  }
}

Where ExtractPublic is covered in Testing chapter. The asyncData and asyncError helpers make sure, that values provided are observed on next macrotask at soonest. This makes methods that would normally perform an HTTP call more alike their non-double counterparts.

// helpers.ts
import { asyncScheduler, Observable, of, throwError } from 'rxjs';
import { observeOn } from 'rxjs/operators';

export function asyncData<TData>(data: TData): Observable<TData> {
  return of(data).pipe(observeOn(asyncScheduler));
}

export function asyncError(err: Error): Observable<never> {
  return throwError(err).pipe(observeOn(asyncScheduler));
}

Subsequently, you can then create doubles for entity specific services by extending the CollectionTestingService:

// entity.testing.service.ts
import { Inject, Injectable } from '@angular/core';
import { AppCollection } from '<path-to-collection>';
import { APP_COLLECTION } from '<path-to-token-definition>';
import { Entity } from '<path-to-entity-model-definition>';
import { EntityService } from '<path-to-entity-service>';
import { ExtractPublic } from '<path-to-extract-public-type>';
import { CollectionTestingService } from '<path-to-collection-testing-service>';

@Injectable()
export class EntityTestingService
  extends CollectionTestingService<Entity>
  implements ExtractPublic<EntityService>
{
  protected ctor = Entity;

  constructor(
    @Inject(APP_COLLECTION) protected readonly collection: AppCollection
  ) {
    super(collection);
  }
}

These can be used in tests for consumers of original entity specific service:

// entity-list.component.spec.ts
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { AppCollection } from '<path-to-collection>';
import { APP_COLLECTION } from '<path-to-token-definition>';
import { Entity } from '<path-to-entity>';
import { EntityService } from '<path-to-entity-service>';
import { EntityTestingService } from '<path-to-entity-service-double>';
import { EntityListComponent } from '<path-to-component>';

describe('EntityListComponent', () => {
  let component: EntityListComponent;
  let fixture: ComponentFixture<EntityListComponent>;
  let collection: AppCollection;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [EntityListComponent],
      providers: [
        {
          provide: APP_COLLECTION,
          useValue: new AppCollection(), // empty mock collection
        },
        {
          provide: EntityService,
          useClass: EntityTestingService, // provide the double instead
        },
      ],
    });
  });

  beforeEach(() => {
    collection = TestBed.inject(APP_COLLECTION);
    collection.add({ name: 'EntityName' }, Entity); // entities available from entity-list.component.ts #getAllModels call
    fixture = TestBed.createComponent(EntityListComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should be created', () => {
    expect(component).toBeTruthy();
  });
});