Unique constraint for Mongoose string schema attribute

Suppose you have the given schema in Mongoose; how does it impact the collection?

import { Schema } from "mongoose";

export interface IString {
  property: string;
}

export const PriceOverhaulSchema = new Schema<IString>({
  property: { type: String, required: false, unique: true },
});

I am curious about the unique constraint's behavior within this schema. If a single document is missing the property field, can another document exist without violating the uniqueness constraint? In other words, does the uniqueness constraint solely apply to documents with the property set, or is it enforced regardless of whether the property is set?

Your insights or clarifications on this issue are greatly appreciated.

Answer №1

Adding the properties required: true, unique: true to a field in a new schema will prompt mongoose to create a unique index when the first document is added to the collection, enforcing uniqueness.

On the other hand, if you use required: false, unique: true on a new schema and create the first document without that field, mongoose will not create the unique index until a document with that field is added later.

However, once the unique index is established, inserting a document without that field will result in mongoose automatically adding a null value to maintain uniqueness.

This means that if you attempt to add another document without including that field, mongoose will trigger an E11000 duplicate key error, since a document with a null value already exists.

Therefore, it seems unnecessary to set a field as required: false when unique: true.

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