loopback/example/client-server/models.js

var loopback = require('../../');

var CartItem = exports.CartItem = loopback.PersistedModel.extend('CartItem', {
  tax: { type: Number, default: 0.1 },
  price: Number,
  item: String,
  qty: { type: Number, default: 0 },
  cartId: Number,
});

CartItem.sum = function(cartId, callback) {
  this.find({ where: { cartId: 1 }}, function(err, items) {
    var total = items
      .map(function(item) {
        return item.total();
      })
      .reduce(function(cur, prev) {
        return prev + cur;
      }, 0);

    callback(null, total);
  });
};

CartItem.remoteMethod('sum',
  {
    accepts: { arg: 'cartId', type: 'number' },
    returns: { arg: 'total', type: 'number' },
  }
);

CartItem.prototype.total = function() {
  return this.price * this.qty * 1 + this.tax;
};