Generic Content Vuex Modules

In my last article, we examined the advantages of a flat Vuex state tree. Today we look at how we can design a system for quickly creating generic Vuex modules for typical CRUD content types.

Often when creating applications, rather sooner than later, we catch ourselves repeating the same boilerplate code over and over again because most of our content types are very similar at their core.

We have several forms for entering data for different content types, which are usually pretty much the same but have different fields. Also, we display the data in the same list or table views with the same sort and filter mechanisms. And we use pretty much the same data fetching logic, but with different API endpoints.

In this article, we try to DRY up one aspect of our codebase by building upon the code from the previous article and making the Vuex part of our application generic and reusable.

Building a Vuex module factory

By using a factory function that creates new Vuex store modules for us, we can reuse all the repeating boilerplate code and pass different implementations of specific dependencies to adapt to the needs of our various content types.

// src/store/modules/crud.js
import Vue from 'vue';

export default function makeCrudModule({
  normalizeRelations = x => x,
  resolveRelations = x => x,
  service
} = {}) {
  return {
    // Actions for `create`, `update` and `delete` omitted for brevity.
    actions: {
      load: async ({ commit }) => {
        // It is not strictly necessary to pass a service,
        // but if none was passed, no data can be loaded.
        if (!service) throw new Error('No service specified!');

        const items = await service.list();
        items.forEach((item) => {
          // Normalize nested data and swap the related objects
          // in the API response with an ID reference.
          commit('add', normalizeRelations(item));
        });
      },
    },
    getters: {
      // Return a single item with the given id.
      find: state => id => {
        // Swap ID referenes with the resolved objects.
        return resolveRelations(state.byId[id]);
      },
      // Return a list of items in the order of `allIds`.
      list: (state, getters) => {
        return state.allIds.map(id => getters.find(id));
      },
    },
    mutations: {
      add: (state, item) => {
        Vue.set(state.byId, item.id, item);
        if (state.allIds.includes(item.id)) return;
        state.allIds.push(item.id);
      },
    },
    namespaced: true,
    state: {
      byId: {},
      allIds: [],
    },
  };
}

Here you can see a typical implementation of a Vuex module for handling the data of a generic content type. If you want to read more about what’s going on here, you can read my previous article, which features pretty much the same code, but in a less generic variant.

Instead of exporting a Vuex store module directly, this module exports a function receiving two methods for resolving and normalizing relations (e.g. an article and its author) and a service responsible for fetching the data (usually from an API endpoint). All of those three parameters are optional.

Using the CRUD module factory

A huge advantage we gain by using factory functions is that we can easily test the methods returned by our crudModuleFactory() because we can simply pass fake implementations of all of their dependencies.

Our src/store/index.js file serves as an integration point and does not contain any complex logic itself, so we can ignore this file in our unit tests without worrying about it.

// src/store/index.js
import Vue from 'vue';
import Vuex from 'vuex';

import { makeNormalizeRelations, makeResolveRelations } from './helpers';
import articleService from '../services/article';
import makeCrudModule from './modules/crud';

Vue.use(Vuex);

const store = new Vuex.Store({ strict: true });

store.registerModule('article', makeCrudModule({
  normalizeRelations: makeNormalizeRelations({
    fields: ['author'],
    store,
  }),
  resolveRelations: makeResolveRelations({
    fields: ['author'],
    store,
  }),
  service: articleService,
}));
store.registerModule('author', makeCrudModule());

export default store;

Because our factory functions for normalizeRelations() and resolveRelations() need access to the state, we have to create the store first before we can register our article and author modules. If we want to add additional content types in the future, we can register new store modules using exactly the same approach.

Take it further

Furthermore we could move all of the code necessary to handle a new content type into a separate directory.

src/
└── modules
    ├── article.js
    ├── author.js
    ├── ...
    └── product.js

// src/modules/article.js
import {
  makeNormalizeRelations,
  makeResolveRelations,
} from '../store/helpers';
import articleService from '../services/article';
import makeCrudModule from '../store/modules/crud';
import makeCrudRoutes from '../router/crud';
import router from '../router';
import store from '../store';

// Register routes.
router.addRoutes(makeCrudRoutes('article'));
// `makeCrudRoutes()` could return something like:
// `[
//    { path: 'articles/list', ... },
//    { path: 'articles/edit/:id', ... },
//  ]`

// Register store module.
store.registerModule('article', makeCrudModule({
  normalizeRelations: makeNormalizeRelations({
    fields: ['author'],
    store,
  }),
  resolveRelations: makeResolveRelations({
    fields: ['author'],
    store,
  }),
  service: articleService,
}));

// ...

Wrapping it up

Usually, making your code DRY helps with keeping it maintainable. But sometimes, as your application evolves, not all of your content types may be as generic as the two we created in this article. In such cases it is important to keep in mind that duplication is far cheaper than the wrong abstraction.

If your content types are vastly different and share only a small amount of logic, you can choose to go a more granular route or even remove the abstraction layer and re establish minor code duplications where it makes sense. A glaring sign of this is when you keep adding more if statements within your abstractions that change the functionality, depending on the value of the parameters you pass to the factory function. Almost always this means that you have an error in your abstraction.

References

• Sandi Metz, The Wrong Abstraction