loopback/common/models/checkpoint.js

/**
 * Module Dependencies.
 */

var PersistedModel = require('../../lib/loopback').PersistedModel
  , loopback = require('../../lib/loopback')
  , assert = require('assert');

/**
 * Properties
 */

var properties = {
  seq: {type: Number},
  time: {type: Date, default: Date},
  sourceId: {type: String}
};

/**
 * Options
 */

var options = {

};

/**
 * Checkpoint list entry.
 *
 * @property id {Number} the sequencial identifier of a checkpoint
 * @property time {Number} the time when the checkpoint was created
 * @property sourceId {String}  the source identifier
 * 
 * @class
 * @inherits {PersistedModel}
 */

var Checkpoint = module.exports = PersistedModel.extend('Checkpoint', properties, options);

/**
 * Get the current checkpoint id
 * @callback {Function} callback
 * @param {Error} err
 * @param {Number} checkpointId The current checkpoint id
 */

Checkpoint.current = function(cb) {
  var Checkpoint = this;
  this.find({
    limit: 1,
    order: 'seq DESC'
  }, function(err, checkpoints) {
    if(err) return cb(err);
    var checkpoint = checkpoints[0];
    if(checkpoint) {
      cb(null, checkpoint.seq);
    } else {
      Checkpoint.create({seq: 0}, function(err, checkpoint) {
        if(err) return cb(err);
        cb(null, checkpoint.seq);
      });
    }
  });
}

Checkpoint.beforeSave = function(next, model) {
  if(!model.getId() && model.seq === undefined) {
    model.constructor.current(function(err, seq) {
      if(err) return next(err);
      model.seq = seq + 1;
      next();
    });
  } else {
    next();
  }
}