normalizr

Normalizes deeply nested JSON API responses according to a schema for Flux application.
Kudos to Jing Chen for suggesting this approach.

Sample App

See flux-react-router-example.

The Problem

• You have a JSON API that returns deeply nested objects;
• You want to port your app to Flux;
• You noticed it's hard for Stores to consume data from nested API responses.

Normalizr takes JSON and a schema and replaces nested entities with their IDs, gathering all entities in dictionaries.

For example,

[{
  id: 1,
  title: 'Some Article',
  author: {
    id: 1,
    name: 'Dan'
  }
}, {
  id: 2,
  title: 'Other Article',
  author: {
    id: 1,
    name: 'Dan'
  }
}]

can be normalized to

{
  result: [1, 2],
  entities: {
    articles: {
      1: {
        id: 1,
        title: 'Some Article',
        author: 1
      },
      2: {
        id: 2,
        title: 'Other Article',
        author: 1
      }
    },
    users: {
      1: {
        id: 1,
        name: 'Dan'
      }
    }
  }
}

Note the flat structure (all nesting is gone).

Features

• Entities can be nested inside other entities, objects and arrays;
• Combine entity schemas to express any kind of API response;
• Entities with same IDs are automatically merged (with a warning if they differ);
• Allows using a custom ID attribute (e.g. slug).

Usage

var normalizr = require('normalizr'),
    normalize = normalizr.normalize,
    Schema = normalizr.Schema,
    arrayOf = normalizr.arrayOf;

First, define a schema for our entities:

var article = new Schema('articles'),
    user = new Schema('users'),
    collection = new Schema('collections');

Then we define nesting rules:

article.define({
  author: user,
  collections: arrayOf(collection)
});

collection.define({
  curator: user
});

Now we can use this schema in our API response handlers:

var ServerActionCreators = {

  // These are two different XHR endpoints with different response schemas.
  // We can use the schema objects defined earlier to express both of them:

  receiveArticles: function (response) {
  
    // Passing { articles: arrayOf(article) } as second parameter to normalize()
    // lets it correctly traverse the response tree and gather all entities:
    
    // BEFORE
    // {
    //   articles: [{
    //     id: 1,
    //     title: 'Some Article',
    //     user: {
    //       id: 7,
    //       name: 'Dan',
    //     }
    //   }, ...]
    // }
    //
    // AFTER:
    // {
    //   result: {
    //    articles: [1, 2, ...] // <--- Note how object array turned into ID array
    //   },
    //   entities: {
    //     articles: {
    //       1: { user: 7, ... }, // <--- Same happens for references to other entities in the schema
    //       2: { ... },
    //       ...
    //     },
    //     users: {
    //       7: { ... },
    //       ..
    //     }
    //   }
    
    var normalized = normalize(response, {
      articles: arrayOf(article)
    });

    AppDispatcher.handleServerAction({
      type: ActionTypes.RECEIVE_ARTICLES,
      normalized: normalized
    });
  },
  
  // Though this is a different API endpoint, we can describe it just as well
  // with our normalizr schema objects:

  receiveUsers: function (response) {

    // Passing { users: arrayOf(user) } as second parameter to normalize()
    // lets it correctly traverse the response tree and gather all entities:
    
    // BEFORE
    // {
    //   users: [{
    //     id: 7,
    //     name: 'Dan',
    //     ...
    //   }, ...]
    // }
    //
    // AFTER:
    // {
    //   result: {
    //    users: [7, ...] // <--- Note how object array turned into ID array
    //   },
    //   entities: {
    //     users: {
    //       7: { ... },
    //       ..
    //     }
    //   }
    

    var normalized = normalize(response, {
      users: arrayOf(users)
    });

    AppDispatcher.handleServerAction({
      type: ActionTypes.RECEIVE_USERS,
      normalized: normalized
    });
  }
}

Finally, different Stores can tune in to listen to all API responses and grab entity lists from action.normalized.entities:

AppDispatcher.register(function (payload) {
  var action = payload.action;

  switch (action.type) {
  case ActionTypes.RECEIVE_ARTICLES:
  case ActionTypes.RECEIVE_USERS:
    mergeUsers(action.normalized.entities.users);
    UserStore.emitChange();
    break;
  }
});

API

####new Schema(key, [options])

Schema lets you define a type of entity returned by your API.
This should correspond to model in your server code.

The key parameter lets you specify the name of the dictionary for this kind of entity.

var article = new Schema('articles');

// You can use a custom id attribute
var article = new Schema('articles', { idAttribute: 'slug' });

####Schema.prototype.define(nestedSchema)

Lets you specify relationships between different entities.

var article = new Schema('articles'),
    user = new Schema('users');

article.define({
  author: user
});

####arrayOf(schema)

Describes an array of the schema passed as argument.

var article = new Schema('articles'),
    user = new Schema('users');

article.define({
  author: user,
  contributors: arrayOf(user)
});

####normalize(obj, schema)

Normalizes object according to schema.
Passed schema should be a nested object reflecting the structure of API response.

var article = new Schema('articles'),
    user = new Schema('users');

article.define({
  author: user,
  contributors: arrayOf(user)
});

// ...

var json = getArticleArray(),
    normalized = normalize(json, arrayOf(article));

Explanation by Example

Say, you have /articles API with the following schema:

articles: article*

article: {
  author: user,
  likers: user*
  primary_collection: collection?
  collections: collection*
}

collection: {
  curator: user
}

Without normalizr, your Stores would need to know too much about API response schema.
For example, UserStore would include a lot of boilerplate to extract fresh user info when articles are fetched:

// Without normalizr, you'd have to do this in every store:

AppDispatcher.register(function (payload) {
  var action = payload.action;

  switch (action.type) {
  case ActionTypes.RECEIVE_USERS:
    mergeUsers(action.rawUsers);
    break;

  case ActionTypes.RECEIVE_ARTICLES:
    action.rawArticles.forEach(rawArticle => {
      mergeUsers([rawArticle.user]);
      mergeUsers(rawArticle.likers);

      mergeUsers([rawArticle.primaryCollection.curator]);
      rawArticle.collections.forEach(rawCollection => {
        mergeUsers(rawCollection.curator);
      });
    });

    UserStore.emitChange();
    break;
  }
});

Normalizr solves the problem by converting API responses to a flat form where nested entities are replaced with IDs:

{
  result: [12, 10, 3, ...],
  entities: {
    articles: {
      12: {
        authorId: 3,
        likers: [2, 1, 4],
        primaryCollection: 12,
        collections: [12, 11]
      },
      ...
    },
    users: {
      3: {
        name: 'Dan'
      },
      2: ...,
      4: ....
    },
    collections: {
      12: {
        curator: 2,
        name: 'Stuff'
      },
      ...
    }
  }
}

Then UserStore code can be rewritten as:

// With normalizr, users are always in action.entities.users

AppDispatcher.register(function (payload) {
  var action = payload.action;

  switch (action.type) {
  case ActionTypes.RECEIVE_ARTICLES:
  case ActionTypes.RECEIVE_USERS:
    mergeUsers(action.normalized.entities.users);
    UserStore.emitChange();
    break;
  }
});

Dependencies

• lodash for isObject and isEqual

Installing

npm install normalizr

Running Tests

npm install -g mocha
npm test