How to default an embedded document to null with mongoose

In Mongoose, when defining a model's schema, you can specify default values for each field. If you want a field's default value to be null, you can use the default keyword when defining the field and set it to null.

Here is an example of how to set a field's default to null:

javascript
const mongoose = require('mongoose');

const schema = new mongoose.Schema({
  name: String,
  age: Number,
  phone: {
    type: String,
    default: null // Set the default value of the phone field to null
  }
});

const User = mongoose.model('User', schema);

// When creating a new User object without providing a value for the phone field, it will default to null.
const user = new User({
  name: 'John Doe',
  age: 30
});

console.log(user.phone); // Output: null

In this example, even if you don't specify a value for the phone field, its default value will be null. When saving to the database, if the phone field is not assigned a value, it will be stored as null.

This approach is typically used when you need to distinguish between a field not being assigned a value and a field being assigned an empty value. By setting the default value to null, you explicitly indicate that the field exists but has not been populated with any value.