@xaamin/forge NPM

Forge

Forge provides a presentation and transformation layer for complex data output, the like found in RESTful APIs. Think of this as a view layer for your Database.

When building an API it is common for people to just grab stuff from the database and expose to the http client. This might be passable for "trivial" APIs but if they are in use by the public, or used by mobile applications then this will quickly lead to inconsistent output.

Goals

Create a protective "barrier" between source data and output, so schema changes do not affect users
Systematic type-casting of data, to avoid foreach ing through and casting everything
Include (a.k.a embedding, nesting or side-loading) relationships for complex data structures
Support the pagination of data results, for small and large data sets alike
Generally ease the subtle complexities of outputting data in a non-trivial API

Install

npm install @xaamin/forge

yarn install @xaamin/forge

Simple Example

For the sake of simplicity, this example has been put together as one simple route function. In reality, you would create dedicated Transformer classes for each model. But we will get there, let's first have a look at this:

import Forge from '@xaamin/forge';

const users = await User.all()

const data = Forge.make()
  .collection(users, user => ({
    firstname: user.first_name,
    lastname: user.last_name
  }))
  .toJSON();

You may notice a few things here: First, we can import Forge, and then call a method collection on it. This method is called a resources and we will cover it in the next section. We pass our data to this method along with a transformer. In return, we get the transformed data back.

Resources

Resources are objects that represent data and have knowledge of a “Transformer”. There are two types of resources:

Item - A singular resource, probably one entry in a data store
Collection - A collection of resources

The resource accepts an object or an array as the first argument, representing the data that should be transformed. The second argument is the transformer used for this resource.

Transformers

The simplest transformer you can write is a callback transformer. Just return an object that maps your data.

const users = await User.all()

const data = Forge.make()
  .collection(users, user => ({
    firstname: user.first_name,
    lastname: user.last_name
  }))
  .toJSON()

But let's be honest, this is not what you want. And we would agree with you, so let's have a look at transformer classes.

Transformer Classes

The recommended way to use transformers is to create a transformer class. This allows the transformer to be easily reused in multiple places.

Creating a Transformer

Create the class yourself, you just have to make sure that the class extends TransformerAbstract and implements at least a transform method.

import { TransformerAbstract } from '@xaamin/forge';

class UserTransformer extends TransformerAbstract {
  transform (model) {
    return {
      id: model.id,
      firstname: model.first_name,
      lastname: model.last_name
    }
  }
}

export default UserTransformer;

Note: A transformer can also return a primitive type, like a string or a number, instead of an object. But keep in mind that including additional data, as covered in the next section, only work when an object is returned.

Using the Transformer

Once the transformer class is defined, it can be passed to the resource as the second argument.

const users = await User.all()

const data = Forge.make()
  .collection(users, new UserTransformer())
  .toJSON();

You have to pass a reference to the transformer class directly.

Note: Passing the transformer as the second argument will terminate the fluent interface. If you want to chain more methods after the call to collection or item you should only pass the first argument and then use the transformWith method to define the transformer. See Fluent Interface

Default Includes

Includes defined in the defaultIncludes will always be included in the returned data.

You have to specify the name of the include by returning an array of all includes from the defaultIncludes. Then you create an additional method for each include, named like in the example: include{Name}.

The include method returns a new resource, that can either be an item or a collection. See Resources.

class BookTransformer extends TransformerAbstract {
  defaultIncludes = [
    'author'
  ];

  transform (book) {
    return {
      id: book.id,
      title: book.title,
      year: book.yr
    }
  }

  includeAuthor(book) {
    return this.item(book.author, new AuthorTransformer());
  }
}

export default BookTransformer;

Note: If you want to use snake_case property names, you would still name the include function in camelCase, but list it under defaultIncludes in snake_case.

Available Include

An availableIncludes is almost the same as a defaultIncludes, except it is not included by default.

class BookTransformer extends TransformerAbstract {
  availableIncludes = [
    'author'
  ];

  transform (book) {
    return {
      id: book.id,
      title: book.title,
      year: book.yr
    }
  }

  includeAuthor (book) {
    return this.item(book.relationships.author, new AuthorTransformer());
  }
}

export default BookTransformer

To include this resource Forge calls the includeAuthor() method before transforming.

return Forge.make()
  .item(book, BookTransformer)
  .include('author')
  .toJSON()

These includes can be nested with dot notation too, to include resources within other resources.

return Forge.make()
  .item(book, BookTransformer)
  .include('author,publisher.something')
  .toJSON()

Eager Loading

When you include additional models in your transformer be sure to eager load these relations as this can quickly turn into n+1 database queries. If you have defaultIncludes you should load them with your initial query. Forge is framework agnostic, so it will not try to load related data.

Metadata

Sometimes you need to add just a little bit of extra information about your model or response. For these situations, we have the meta method.

const users = await User.all()

return Forge.make()
  .collection(users, UserTransformer)
  .meta({
    access: 'limited'
  })
  .toJSON()

How this data is added to the response is dependent on the Serializer.

DataSerializer

This serializer adds the data namespace to all of its items:

// Item
{
  data: {
    foo: 'bar',
    included: {
      data: {
        name: 'test'
      }
    }
  }
}

// Collection
{
  data: [
    {
      foo: bar
    },
    {...}
  ]
}

The advantage over the PlainSerializer is that it does not conflict with meta and pagination:

// Item with meta
{
  data: {
    foo: 'bar'
  },
  meta: {
    ...
  }
}

// Collection
{
  data: [
    {...}
  ],
  meta: {...},
  pagination: {...}
}

SLDataSerializer

This serializer works similarly to the DataSerializer, but it only adds the data namespace on the first level.

// Item
{
  data: {
    foo: 'bar',
    included: {
      name: 'test'
    }
  }
}

Fluent Interface

Forge has a fluent interface for all the setter methods. This means you can chain method calls which makes the API more readable. The following methods are available on Forge.make() (see below).

Chainable methods: