Mongo schema, array of string with unique values - arrays

Question

I'm creating the schema for a mongo document and I can do everything except prevent duplicates in a non-object array.
I'm aware of the addToSet, but I'm referring to Mongo Schema.
I don't want to check on Update using $addToSet, rather I want this to be part of my schema validation.
Example below.
let sampleSchema = {
name: { type: 'String', unique: true },
tags: [{ type: 'String', unique: true }]
}
The above snippet prevents name from having duplicate values. It allows tags to be stored as a string array.
But.. I cannot limit the array to be unique strings.
{ name: 'fail scenario', tags: ['bad', 'bad', 'array']}
I'm able to insert this record which should be a fail scenario.

Answer 1

const express = require('express');
const router = express.Router();
const mongoose = require('mongoose');
const _ = require('underscore');
let sampleSchema = new mongoose.Schema({
name: {
type: 'String',
unique: true
},
tags: [{
type: 'String'
}]
})
sampleSchema.pre('save', function (next) {
this.tags = _.uniq(this.tags);
next();
});
const Sample = mongoose.model('sample', sampleSchema, 'samples');
router.post('/sample', function (req, res, next) {
const sample = new Sample(req.body);
sample.save()
.then((sample) => {
return res.send(sample);
})
.catch(err => {
return res.status(500).send(err.message);
})
});

Answer 2

I've come to the conclusion that this is impossible to do via Mongoose Schema.
JSON schema is done like so.
let schema = {
name: { type: 'string' }
tags: {
type: 'array',
items: { type: 'string', uniqueItems: true }
}
}
I'll validate with JSON schema before creating Mongo Document.

Answer 3

This method builds on Med's answer, handles references, and done completely in scheme validation.
let sampleSchema = new mongoose.Schema({
strings: [{type: 'String'}],
references: [{type: mongoose.Schema.Types.ObjectId, ref: 'Reference'],
});
sampleSchema.pre('save', function (next) {
let sample = this;
sample.strings = _.uniq(sample.strings, function(i) {return (i._id) ? i._id.toString() : i;});
sample.references = _.uniq(sample.references, function(i) {return (i._id) ? i._id.toString() : i;});
return next();
});

Answer 4

I'm a little late, but maybe this will help someone in the future.
const mongoose = require('mongoose');
const userSchema = new mongoose.Schema({
name: {
type: String,
},
reference: {
type: [mongoose.Schema.Types.ObjectId],
ref: 'SomeOtherSchema',
// Add a custom validator.
validate: {
// The actual validator function goes here.
// "arr" will be the value that's being validated (so an array of
// mongoose new ObjectId statements, in this case).
validator: arr => {
// Convert all of the items in the array "arr", to their string
// representations.
// Then, use those strings to create a Set (which only stores unique
// values).
const s = new Set(arr.map(String));
// Compare the Set and Array's sizes, to see if there were any
// duplicates. If they're not equal, there was a duplicate, and
// validation will fail.
return s.size === arr.length;
},
// Provide a more meaningful error message.
message: p => `The values provided for '${ p.path }', ` +
`[${ p.value }], contains duplicates.`,
}
},
});
The above commented code should be pretty self explanatory.

Answer 5

With the newer version(s) of MongoDB, you can use $addToSet to append to an array if and only if the new value is unique compared to the items of the array.
Here's the reference: https://www.mongodb.com/docs/manual/reference/operator/update/addToSet/
Here's an example:
const SampleSchema = new mongoose.Schema({
tags: [String]
});
const Sample = mongoose.model('Sample', SampleSchema);
// append to array only if value is unique
Sample.findByIdAndUpdate({_id: 1, {$addToSet: {tags: "New Tag"}}});
This will effectively update the tags if the "New Tag" is not already present in the tags array. Otherwise, no operation is done.