A mixin to enable loopback Model properties to be marked as changed.
Last updated 4 years ago by mrfelton .
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This module is designed for the Strongloop Loopback framework. It provides a mixin that makes it possible to trigger a function if selected model properties change.

The property value is an object that details model properties to be watched as well as the callback function to be trigged.


npm install --save loopback-ds-changed-mixin


Add the mixins property to your server/model-config.json:

  "_meta": {
    "sources": [
    "mixins": [


To use with your Models add the mixins attribute to the definition object of your model config.

    "name": "Widget",
    "properties": {
        "name": "String",
        "description": "String",
        "status": "String"
    "mixins": {
        "Changed": {
            "properties": {
                "name": "changeName",
                "status": "changeStatus",

In the above, if the status property is modified on one of more model instances, the function that is defined at the property will be executed with a ChangeSet as a parameter.

// The ChangeSet object passed here has several helper methods    
function changeName(changeSet) {

    // Return an array of all the ID's in this change set

    // Return an object with all the ID's and their new values

    // Return the value for a given ID

    // Return an array of all the unique values in this change set

    // Return an object with all the Values and an array of the ID's changed to this value

    // Return an array of all the ID's changed to a given value

    // The raw data is available as well



The specific fields that are to be marked as changed can be set by passing an object to the mixin options.

In this example we mark the status and productId properties for change notifications. The value of each property defined here is the name of the callback method that is invoked when changes on that property is detected.

  "name": "Widget",
  "properties": {
      "name": "String",
      "description": "String",
      "status": "String"
  "mixins": {
    "Changed": {
      "properties": {
        "name": "changeName",
        "status": "changeStatus",

You can selectively skip the changed mixin behavior in calls to loopback update methods by setting the skipChange option. This can be a boolean to skip the behavior on all properties, a string to skip the behavior for a single property, or an array or object to skip the behavior for multiple properties.

instance.save({skipChanged: true}); // skip behavior
instance.save({skipChanged: 'name'}); // skip behavior for the properties.
instance.save({skipChanged: ['name', 'status']}); // skip behavior for name and status properties.
instance.save({skipChanged: {name: true, status: true}}); // skip behavior for name and status properties.


Run the tests in test.js

  npm test

Run with debugging output on:

  DEBUG='loopback-ds-changed-mixin' npm test

Run the test with a mongodb datasource

  MONGODB_URL=mongodb://localhost/ds_changed_mixin npm test

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