Loopback JSON Schema

Adds JSON Schema support to LoopBack.

Installing

npm install @globocom/loopback-jsonschema

Setup

Initializing

Add the following code after calling app.boot();

var loopbackJsonSchema = require('loopback-jsonschema');
loopbackJsonSchema.init(app);
loopbackJsonSchema.enableJsonSchemaMiddleware(app);

Configuring a DataSource

Add a loopbackJsonSchemaDb entry to the datasources.json file with your data source configuration. If no loopbackJsonSchemaDb entry is found, we fallback to using the default memory data source.

Overriding the default base model

By default, Loopback's Model is used as the base for dynamically defined models. It is possible to override this by passing a custom implementation to the init function:

loopbackJsonSchema.init(app, { Model: MyCustomModel });

Hook: beforeRegisterLoopbackModel

Immediately before registering a Loopback model from an item schema, the method ItemSchema#beforeRegisterLoopbackModel(app, JsonSchemaModel, callback) is called. This hook can be used for any customizations that are needed before a model is registered.

Overriding the default collection schema

It is possible to override the default collection schema by passing a custom CollectionSchema implementation to the init function:

loopbackJsonSchema.init(app, { CollectionSchemaClass: MyCustomCollectionSchema });

var util = require('util');
var CollectionSchema = require('loopback-jsonschema/lib/domain/collection-schema');

function MyCustomCollectionSchema() {
    CollectionSchema.apply(this, Array.prototype.slice.call(arguments));
};

util.inherits(MyCustomCollectionSchema, CollectionSchema);
// It's required to set the value of "pluralModelName". This value will be used on the headers. You can still use the default value (see below).
MyCustomCollectionSchema.pluralModelName = MyCustomCollectionSchema.super_.pluralModelName;

// Override functions to customize the default collection schema.

Have a look at https://github.com/globocom/loopback-jsonschema/blob/master/lib/domain/collection-schema.js for available functions to override.

Using

Dynamically defining Loopback models from a JSON Schema

To dynamically define a new Loopback model just create a new instance of the ItemSchema model provided by loopback-jsonschema. Doing this via the REST interface is as simples as POSTing a valid JSON Schema, as follows:

# person.json
{
  "type": "object",
  "title": "Person",
  "collectionTitle": "People",
  "collectionName": "people",
  "properties": {
    ...
  }
}

# Create a Person model from a JSON Schema
curl -i -XPOST -H "Content-Type: application/json" http://example.org/api/item-schemas -T person.json

The people collection will then be available at http://example.org/api/people.

Item and Collection schemas

Once a Loopback model has been defined, Item and Collection schemas describing a single item and a collection of items, respectively, are automatically available.

Item Schema example

$ curl -i http://example.org/api/item-schemas/people
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 577
ETag: "-912870715"
Date: Mon, 19 May 2014 19:07:14 GMT
Connection: keep-alive

{
  "id": "537530ea27f8870b63f2d886",
  "type": "object",
  "title": "Person",
  "collectionTitle": "People",
  "collectionName": "people",
  "links": [
    {
      "rel": "self",
      "href": "http://example.org/api/people/{id}"
    },
    {
      "rel": "item",
      "href": "http://example.org/api/people/{id}"
    },
    {
      "rel": "update",
      "method": "PUT",
      "href": "http://example.org/api/people/{id}"
    },
    {
      "rel": "delete",
      "method": "DELETE",
      "href": "http://example.org/api/people/{id}"
    }
  ],
  "$schema": "http://json-schema.org/draft-04/hyper-schema#"
}

Collection Schema example

$ curl -i http://example.org/api/collection-schemas/people
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/schema+json; charset=utf-8
Content-Length: 373
ETag: "-833543453"
Date: Wed, 11 Jun 2014 20:10:41 GMT
Connection: keep-alive

{
  "$schema": "http://json-schema.org/draft-04/hyper-schema#",
  "title": "People",
  "type": "array",
  "items": {
    "$ref": "http://example.org/api/item-schemas/people"
  },
  "links": [
    {
      "rel": "self",
      "href": "http://example.org/api/people"
    },
    {
      "rel": "add",
      "method": "POST",
      "href": "http://example.org/api/people",
      "schema": {
        "$ref": "http://example.org/api/item-schemas/people"
      }
    },
    {
      "rel": "previous",
      "href": "http://example.org/api/people?filter[limit]={limit}&filter[offset]={previousOffset}{&paginateQs*}"
    },
    {
      "rel": "next",
      "href": "http://example.org/api/people?filter[limit]={limit}&filter[offset]={nextOffset}{&paginateQs*}"
    },
    {
      "rel": "page",
      "href": "http://example.org/api/people?filter[limit]={limit}&filter[offset]={offset}{&paginateQs*}"
    },
    {
      "rel": "order",
      "href": "http://example.org/api/people?filter[order]={orderAttribute} {orderDirection}{&orderQs*}"
    }
  ]
}

Default values and read-only properties

It's possible to use readOnly property to indicate that the instance property should not be changed (if it has a value of boolean true).

It's possible to use default property to indicate that when the instance property is not passed the default value will be used.

If the schema indicates that the property has both readOnly: true and default values defined, the default value will be used.

For example:

{
    "title": "Bikes Rules",
    "type": "object",
    "$schema": "http://json-schema.org/draft-04/hyper-schema#",
    "collectionName": "bikes",
    "name": "My Awesome Bikes!",
    "properties": {
        "brand": {
            "description": "Brand of the bike",
            "default": "kawasaki",
            "type": "string"
        },
        "cc": {
            "description": "Cubic Centimeters",
            "default": "120",
            "readOnly": true,
            "type": "integer"
        },
        "name": {
            "description": "Name of the bike",
            "readOnly": false,
            "type": "string"
        }
    }
}

curl -XPOST -H "Content-Type: application/json" http://example.org/api/bikes -d'
{
    "cc": 350,
    "name": "Ninja"
}'

The output will be:

{
    id: "5460b29652fe613c00f23f75",
    created: "2014-11-10T12:41:58.344Z",
    modified: "2014-11-10T12:41:58.344Z",
    name: "Ninja",
    brand: "kawasaki",
    cc: 120
}

Default links

Item and collection schemas have a default set of links which correspond to the basic CRUD operations supported by Loopback.

Including custom links in an item schema

It is possible to include custom links in an item schema. To do so, just include them in the links property of the item schema used to define a Loopback model:

{
  "type": "object",
  ...
  "properties": {
    ...
  },
  "links": [
    {
      "rel": "my-custom-item-schema-link",
      "href": "http://example.org/my/custom/item-schema-link"
    }
  ]
}

Including custom links in a collection schema

It is possible to include custom links in a collection schema. To do so, just include them in the collectionLinks property of the item schema used to define a Loopback model:

{
  "type": "object",
  ...
  "properties": {
    ...
  },
  "collectionLinks": [
    {
      "rel": "my-custom-collection-schema-link",
      "href": "http://example.org/my/custom/collection-schema-link"
    }
  ]
}

Instance/Schema correlation

Every request for an instance is automatically correlated to its schema according to the recommendation of the JSON Schema spec.

Instance Validation

Once a Item Schema has been defined all instances created or updated will be validated according the schema. In case of validation error loopback-jsonschema will return an error message following loopback error message format.

This module supports both drafts: Draft-4(default) and Draft-3. The error messages and codes try to follow the messages/codes returned by the module tv4.

If you want to use draft-3, you need to override the $schema property, for instance:

{
  "$schema": "http://json-schema.org/draft-03/hyper-schema#",
  "type": "object",
  ...
  "properties": {
    "name": {
      "type": "string",
      "title": "Full name"
     }
   ...
  }
}

Indexes

It's possible to create indexes by adding a key called indexes.

See Indexes in Loopback documentation for more information.

{
    "type": "object",
    "title": "Task",
    "collectionTitle": "To-Do List",
    "collectionName": "tasks",
    "properties": {
        "title": {
          "title": "Title",
          "type": "string"
        },
        "slug": {
          "title": "Slug",
          "type": "string"
        },
        "value": {
          "title": "Value",
          "type": "integer"
        }
    },
    "indexes": {
        "title_value_index": {
            "keys": {"title": 1, "value": -1}
        },
        "title_index": {"title": 1},
        "slug_index": {
            "keys": {"slug": 1},
            "options": {"unique": true}
        }
    }
}

Sample App

An example running LoopBack with this module: https://github.com/globocom/loopback-jsonschema-example

Disclaimer

This project is very much in an alpha stage at the moment. But it is being actively developed. Contributions (code, documentation, issues, etc.) are very welcome.

References

http://json-schema.org/