Mongoose Schema: enforcing mutually exclusive keys

Question

The data my API will receive contains one of two keys, option1 or option2, but not both.

I want to enforce that behaviour in my mongoose schema but have found nothing that would do this, is there a way to link two keys and make sure one (and only one) of them exists?

Example code:

const exampleSchema = new mongoose.Schema({
  custRef: {
    type: String,
    required: true,
    trim: true
  },
  option1: {
    type: Number
  },
  option2: {
    type: Number
  }
});

Example JSON 1:

{
    "custRef": "abc123",
    "option1": 456
}

Example JSON 2:

{
    "custRef": "abc789",
    "option2": 010
}

Answer 1

You can use a pre validate hook like this:

(note that I removed custRef field for simplicity)

const mongoose = require("mongoose");

const exampleSchema = new mongoose.Schema({
  option1: {
    type: Number
  },
  option2: {
    type: Number
  }
});

exampleSchema.pre("validate", function(next) {
  //console.log(this);
  if (this.option1 && this.option2) {
    let err = new Error("Both options not allowed");
    err.status = 400;
    next(err);
  } else if (!(this.option1 || this.option2)) {
    let err = new Error("One of the options is required");
    err.status = 400;
    next(err);
  }

  next();
});

const Example = mongoose.model("Example", exampleSchema);

const example = new Example({});

example.validate().catch(err => {
  console.log(err.message);
});

This may not work for update operations, so be careful.

Docs:

https://mongoosejs.com/docs/middleware.html#order