Mongo schema, array of string with unique values

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.

Possible duplicate of [Mongoose Unique values in nested array of objects](http://stackoverflow.com/questions/15921700/mongoose-unique-values-in-nested-array-of-objects) — Karlen, Jan 22 '17 at 08:44
I'm aware of the $addToSet, but I'm referring to Mongo Schema. — Proximo, Jan 22 '17 at 13:13

Med Lazhari · Accepted Answer · 2020-07-11T18:08:16.697

8

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);
    })
});

edited Jul 11 '20 at 18:08

answered Jan 22 '17 at 13:30

Med Lazhari

608
5
9

Thanks for the answer but I'm trying to do this with only Schema, not code and not with flags on save, update methods of mongoose. – Proximo Jan 22 '17 at 14:10
In underscore, it's _.uniq not _.unique. Also, here is a revised version that works with references: `this.tags = _.uniq(this.tags, function(i) {return (i._id) ? i._id.toString() : i;});` – BuffMcBigHuge Aug 08 '17 at 17:10

Proximo · Answer 2 · 2017-01-22T15:27:14.387

4

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.

edited Jan 22 '17 at 15:27

answered Jan 22 '17 at 15:22

Proximo

6,235
11
49
67

score 2 · Answer 3 · answered Aug 08 '17 at 17:19

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();

});

score 2 · Answer 4 · answered Jun 05 '22 at 19:16

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.

score 1 · Answer 5 · answered Jan 04 '23 at 21:29

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.

Mongo schema, array of string with unique values

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