getters-setters.md

Getters/Setters in Mongoose

Mongoose getters and setters allow you to execute custom logic when getting or setting a property on a Mongoose document. Getters let you transform data in MongoDB into a more user friendly form, and setters let you transform user data before it gets to MongoDB.

Getters

Suppose you have a User collection and you want to obfuscate user emails to protect your users' privacy. Below is a basic userSchema that obfuscates the user's email address.

[require:getters/setters.*getters.*basic example]

Keep in mind that getters do not impact the underlying data stored in MongoDB. If you save user, the email property will be 'ab@gmail.com' in the database.

By default, Mongoose executes getters when converting a document to JSON, including Express' res.json() function.

app.get(function(req, res) {
  return User.findOne().
    // The `email` getter will run here
    then(doc => res.json(doc)).
    catch(err => res.status(500).json({ message: err.message }));
});

To disable running getters when converting a document to JSON, set the toJSON.getters option to false in your schema as shown below.

const userSchema = new Schema({
  email: {
    type: String,
    get: obfuscate
  }
}, { toJSON: { getters: false } });

To skip getters on a one-off basis, use user.get() with the getters option set to false as shown below.

[require:getters/setters.*getters.*skip]

Setters

Suppose you want to make sure all user emails in your database are lowercased to make it easy to search without worrying about case. Below is an example userSchema that ensures emails are lowercased.

[require:getters/setters.*setters.*basic]

Mongoose also runs setters on update operations, like updateOne(). Mongoose will upsert a document with a lowercased email in the below example.

[require:getters/setters.*setters.*updates]

In a setter function, this can be either the document being set or the query being run. If you don't want your setter to run when you call updateOne(), you add an if statement that checks if this is a Mongoose document as shown below.

[require:getters/setters.*setters.*update skip]

Passing Parameters using $locals

You can't pass parameters to your getter and setter functions like you do to normal function calls. To configure or pass additional properties to your getters and setters, you can use the document's $locals property.

The $locals property is the preferred place to store any program-defined data on your document without conflicting with schema-defined properties. In your getter and setter functions, this is the document being accessed, so you set properties on $locals and then access those properties in your getters examples. For example, the following shows how you can use $locals to configure the language for a custom getter that returns a string in different languages.

[require:getters/setters.*localization.*locale]

Differences vs ES6 Getters/Setters

Mongoose setters are different from ES6 setters because they allow you to transform the value being set. With ES6 setters, you would need to store an internal _email property to use a setter. With Mongoose, you do not need to define an internal _email property or define a corresponding getter for email.

[require:getters/setters.*setters.*vs ES6]