Prevent field modification with Mongoose Schema

Question

Is there any way to set a field with an "unmodifiable" setting (Such as type, required, etc.) when you define a new Mongoose Schema? This means that once a new document is created, this field can't be changed.

For example, something like this:

var userSchema = new mongoose.Schema({
  username: {
    type: String,
    required: true,
    unmodifiable: true
  }
})

Answer 1

From version 5.6.0 of Mongoose, we can use immutable: true in schemas (exactly as the aforementioned answer on mongoose-immutable package). Typical use case is for timestamps, but in your case, with username it goes like this:

const userSchema = new mongoose.Schema({
  username: {
    type: String,
    required: true,
    immutable: true
  }
});

If you try to update the field, modification will be ignored by Mongoose.

---

Going a little further than what have been asked by OP, now with Mongoose 5.7.0 we can conditionally set the immutable property.

const userSchema = new mongoose.Schema({
  username: {
    type: String,
    required: true,
    immutable: doc => doc.role !== 'ADMIN'
  },
  role: {
    type: String,
    default: 'USER',
    enum: ['USER', 'MODERATOR', 'ADMIN'],
    immutable: true
  }
});

Sources: What's New in Mongoose 5.6.0: Immutable Properties and What's New in Mongoose 5.7: Conditional Immutability, Faster Document Arrays.