[Solved] Add Property to Object that is returned by Sequelize FindOne

I am trying to add a property to a sequelize instance before passing it back to the client.

router.get('/cats/1', function (req, res) {
    Cat.findOne({where: {id: 1}})
        .then(function (cat) {
            // cat exists and looks like {id: 1}
            cat.name = "Lincoln";
            // console.log of cat is {id: 1, name: Lincoln}

The client only see’s {id: 1} and not the newly added key.

  • What is going on here?
  • What type of Object is returned by Sequelize?
  • How can I add new properties to my Cats and send them back?
Solution #1:

The Sequelize Model class (of which your cats are instances) has a toJSON() method which res.json will presumably use to serialise your cats. The method returns the result of Model#get() (https://github.com/sequelize/sequelize/blob/95adb78a03c16ebdc1e62e80983d1d6a204eed80/lib/model.js#L3610-L3613), which only uses attributes defined on the model. If you want to be able to set the cats name, but not store names in the DB, you can use a virtual column when defining your cat model:

sequelize.define('Cat', {
  // [other columns here...]
  name: Sequelize.VIRTUAL

Alternatively, if you don’t want to add properties to the model definition:

cat = cat.toJSON(); // actually returns a plain object, not a JSON string
cat.name = 'Macavity';
Solution #2:

The following works for sequelize v4.

const order = Order.findOne(criteria);
order.setDataValue('additionalProperty', 'some value');

Hope this helps. It’s a bit late but in case people are still looking for answers.

Respondent: Eric Xin Zhang
Solution #3:

What works for me is to use setDataValue

router.get('/cats/1', function (req, res) {
    Cat.findOne({where: {id: 1}})
        .then(function (cat) {
            cat.setDataValue("name", "Lincoln");

Specs for the function

public setDataValue(key: string, value: any)

Update the underlying data value


Name    Type    Attribute   Description
key     string              key to set in instance data store   
value   any                 new value for given key

Source: https://sequelize.org/master/class/lib/model.js~Model.html#instance-method-setDataValue

Respondent: 7hibault
Solution #4:

It won’t let me comment on the correct answer above (https://stackoverflow.com/a/38469390/562683), just wanted to add a use case where this helped me.

I have an existing mysql database that we cannot change the schema of (has to work with the old system and the new system until we can deprecate the old system) but we’ve layered MonogoDB as well for additional features until we can do a system refactor.

The answer above of the Virtual property helped because i’d basically make a placeholder for the mongo db information (in this case, an object activity log) and add it on the ‘findMyObject’ service call.

For example:

const model = sequelize.define('myobj', {
  id: {
    type: Sequelize.INTEGER,
    autoIncrement: true,
    primaryKey: true,
    field: 'eventId',
  name: { type: Sequelize.STRING, allowNull: false },
  history: Sequelize.VIRTUAL,

Then in the MyObjectService, findMyObject call:

const result = yield MyObject.findOne(query);
result.history = yield getMyObjectHistoryArray(id);
return result;

And the resultant JSON looks like:

  "id": 1,
  "name": "My Name",
  "history": [ 

So we were able to extend the object without changing the db, but still have an object in the backend where you can go:

let obj = yield findMyObject(id);
obj.name = "New Name";
return yield obj.save();  

Which you wouldn’t be able to do if, in the findMyObject function, you either did {raw: true} or result.get({plain: true})

Respondent: James Cori
Solution #5:

you can use toJSON() to convert Sequelize object into JSON type and then add properties as we do in js

Example :

     .then(function (userIns) {

        // here userIns is Sequelize Object 
        // and data is Json Object

        let data = userIns.toJSON();
        data['displayName'] = 'John';

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

Leave a Reply

Your email address will not be published.