How to create item if not exists and return an error if exists

Question

I\'m writing alexa skill and would like to check if user exists in MongoDB. My code works but I don\'t know how to define situation if user is already in a database :(

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Answer 1

It sounds like what you really want is a unique key constraint and not an upsert.

The unique key can be set in [mongoose] with either the schema field options:

const s = new Schema({ name: { type: String, unique: true }});

or by the index method:

Schema.path('name').index({ unique: true });

If an attempt is made to create a document that already has an entry for that key then an error will be thrown:

NOTE: violating the constraint returns an E11000 error from MongoDB when saving, not a Mongoose validation error.