json-schema-deref

Dereference JSON pointers in a JSON schemas with their true resolved values. A lighter synchronous version of this module is available as json-schema-deref-sync, but omits web references and custom loaders.

Installation

npm install json-schema-deref

Overview

Let's say you have the following JSON Schema:

{
  "description": "Just some JSON schema.",
  "title": "Basic Widget",
  "type": "object",
  "definitions": {
    "id": {
      "description": "unique identifier",
      "type": "string",
      "minLength": 1,
      "readOnly": true
    }
  },
  "properties": {
  "id": {
    "$ref": "#/definitions/id"
  },
  "foo": {
    "$ref": "http://www.mysite.com/myschema.json#/definitions/foo"
  },
  "bar": {
    "$ref": "bar.json"
  }
}

Sometimes you just want that schema to be fully expanded, with $ref's being their (true) resolved values:

{
  "description": "Just some JSON schema.",
  "title": "Basic Widget",
  "type": "object",
  "definitions": {
    "id": {
      "description": "unique identifier",
      "type": "string",
      "minLength": 1,
      "readOnly": true
    }
  },
  "properties": {
    "id": {
      "description": "unique identifier",
      "type": "string",
      "minLength": 1,
      "readOnly": true
    },
    "foo": {
      "description": "foo property",
      "readOnly": true,
      "type": "number"
    },
    "bar": {
      "description": "bar property",
      "type": "boolean"
    }
  }
}

This utility lets you do that:

var deref = require('json-schema-deref');
var myschema = require('schema.json');

deref(myschema, function(err, fullSchema) {
  console.dir(fullSchema); // has the full expanded $refs
};

API

deref(schema, options, fn)

Dereferences $ref's in json schema to actual resolved values. Supports local, file and web refs.

Parameters:

schema

The input JSON schema

options

baseFolder - the base folder to get relative path files from. Default is process.cwd()

cache - whether to cache the result from web requests. true if to cache, false otherwise.

cacheTTL - the time in milliseconds to keep web request results in cache. Default is 5 minutes.

loader - a function for custom loader. Invoked if we could not resolve the ref type, or if there was an error resolving a web or file ref types. function with signature: function(refValue, options, fn)

• refValue - the string value of the ref being resolved. Ex: db://my_database_id
• options - options parameter passed to deref
• fn - The final callback function, in form function(err, newValue)
  • err - error if ref is valid for the loader but there was an error resolving the ref
  • newValue - the resolved ref value, or null/undefined if the ref isn't for this custom loader and we should just leave the $ref as is.

fn

The final callback function(err, fullSchema)

deref.getRefPathValue(schema, refPath)

Gets the "local" ref value given the path.

schema - the (root) json schema to search

refPath - string ref path to get within the schema. Ex. #/definitions/id

var localValue = deref.getRefPathValue(myschema, '#/definitions/foo');
console.dir(localValue);

Custom Loader

Let's say we want to get $ref's from a MongoDB database, and our $ref objects in the JSON Schema might be something like:

"foo": {
  "$ref":"mongodb:507c35dd8fada716c89d0013"
}

Our custom loader function passed in the options loader parameter would look something like:

function myMongoDBLoader(ref, option, fn) {
  if(ref.indexOf('mongodb:') === 0) {
    var id = ref.substring(8);
    return collection.findOne({_id:id}, fn);
  }

  // not ours, pass back nothing to keep it the same
  return fn();
}