How can I use partialFilterExpression on a mongoose model

Question

I have created a mongoose model that has an email field. I want it to be unique if a value is provided by a user but I want it to be empty is a user has not provided any value. I have found a good mongodb reference here: https://docs.mongodb.com/manual/core/index-partial/#partial-index-with-unique-constraints that could work but I don't know how to make it work on mongoose

This is how the field looks like right now

email: {
    type: String,
    index: true,
    unique: true
  }

If I leave it the way it is, I cant create multiple documents with an empty/null email field

Answer 1

In the email path level, you can use only:

email: {
  type: String
}

And in the schema level use:

SchemaName.index({ email: 1 }, {
  unique: true,
  partialFilterExpression: {
    'email': { $exists: true, $gt: '' }
  }
});

This way the unique constraint is applied only if email exists and is not an empty string

Answer 2

You can have something like :

email: {
    type: String,
    index: {
      unique: true,
      partialFilterExpression: { email: { $type: 'string' } },
    },
    default : null
  }

but do read below link, before you actually implement it, as defaults seems to work only on new document inserts :-

Mongoose v5.6.9 Documentation