Racer plugin for schema validation module for ShareDB
Last updated 2 days ago by yska .
MIT · Bugs · Original npm · Tarball · package.json
$ cnpm install @startupjs/sharedb-schema 
SYNC missed versions from official npm registry.


  • Racer plugin for schema validation module for ShareDB
  • Uses z-schema, which supports JSON-Schema v4
  • Schema validation executes in sync validate hook, so you validate the actual result of operation
  • Supports custom validators with async and sync logic
  • Custom validators can preload data in async hook to use it later in sync

Known Issues

  • Works only with JSON OT type
  • Format functions should be sync
  • For every op the whole doc validates each time, because it`s the only case when z-schema returns full path to wrong fields

How it works

Current 0.7 version of ShareJS has 4 hooks which are executed while operation is applied.

  • async submit hook - executes once before op is applied to data snapshot in db. This is convinient place to preload data and execute async validation logic. Be aware that you can not have result of operation here. It`s ok for some ops (model.set, model.add) because they ovewrites previous data (or add new), but for array mutators (model.push, model.pop, etc), string mutators (model.stringInsert, model.stringRemove) and increment (model.increment) it`s impossible to predict what will be the result data and we can not use some kinds of validators here because of this, like max, min, etc. That`s why we should use sync hook.
  • sync preValidate hook - executes before op actually applied to snapshot. In high concurent cases it can be executed more than one time. We still does not have result data here, so it`s useless for us.
  • sync validate hook - executes after op is applied to snapshot, but before these changes are saved to db. Can be executed more than one time. It`s best place for schema validation logic as we have result data here which is not saved to db yet
  • async after submit hook - executes once after changes are saved to db. It`s useless for validation, but good to trigger some stuff

All schema validation logic executes in validate hook. Custom validators have two methods: .sync - sync and executes in validate hook and .async - async and executes in submit hook. There can be one of them or both, also you can preload data in .async method to use it later in .sync


yarn add @startupjs/sharedb-schema


Step 1. Options

var options = {
  schemas: {
    users: {
      title: 'Example Schema',
    type: 'object',
    properties: {
      nickname: {
        type: 'string',
        format: 'xstring', // custom format
        minLength: 1,
        maxLength: 10,
      email: {
        type: 'string',
        format: 'email',
      age: {
        description: 'Age in years',
        type: 'integer',
        minimum: 0,
      roleId: {
        type: 'string',
        collection: 'roles', // additional field for 'join' custom validator
        validators: ['join'], // custom validators
      hobbies: {
        type: 'array',
        maxItems: 3,
        items: {
          type: 'string',
        uniqueItems: true,
    required: ['email'],
  // JSON-Schema formats can be added here. They should be sync
  formats: {
    xstring: function(str) {
      return str !== 'xxx';
  // Custom validators
  validators: {
    // join - is working example of custom validator. It ensures that value is id of doc of specific collection
    join: {
      async: function (context, done) {
        var id = context.value // here is value for this op
        if (!id) return done()
        var collection = context.schema.collection // context.schema - is schema of current property
        var model = this.store.createModel()
        var $entity = model.at(collection + '.' + id)
        model.fetch($entity, function (err) {
          if (err) return done(err)
          if (!$entity.get()) {
            return done(Error('No ' + collection + ' with id ' + id))
    // this is example of custom validator, that preloads data and uses it later
    preload: {
      async: function (context, done) {
        var model = this.store.createModel() // that`s how to get model
        var $someData = model.at('some.path')
        model.fetch($someData, function (err) {
          if (err) return done(err)
          var data = $someData.get()
          done(null, data) // pass data as second parameter
      sync: function (value, context) {
        var data = context.data // preloaded data is here

        return true || false

Step 2. Plugin

add the sharedbSchemaInit function to your server/index.js

const sharedbSchemaInit = require('@startupjs/sharedb-schema')

and then call this function in the backend event

eventEmitter.on('backend', async backend => {
  sharedbSchemaInit(backend, options)

The MIT License

Copyright (c) 2016 Pavel Zhukov

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