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mongoose-unique-validator

mongoose-unique-validator is a plugin which adds pre-save validation for unique fields within a Mongoose schema.

mongoose-unique-validator

mongoose-unique-validator is a plugin which adds pre-save validation for unique fields within a Mongoose schema.

This makes error handling much easier, since you will get a Mongoose validation error when you attempt to violate a unique constraint, rather than an E11000 error from MongoDB.

npm install mongoose-unique-validator

Then, simply apply the plugin to your schema:

var mongoose = require('mongoose');
var uniqueValidator = require('mongoose-unique-validator');
 
var mySchema = mongoose.Schema(/* put your schema definition here */);
mySchema.plugin(uniqueValidator);

Let’s say you have a user schema. You can easily add validation for the unique constraints in this schema by applying the uniqueValidator plugin to your user schema:

var mongoose = require('mongoose');
var uniqueValidator = require('mongoose-unique-validator');
 
// Define your schema as normal. 
var userSchema = mongoose.Schema({
    username: { type: String, required: true, unique: true },
    email: { type: String, index: true, unique: true, required: true },
    password: { type: String, required: true }
});
 
// Apply the uniqueValidator plugin to userSchema. 
userSchema.plugin(uniqueValidator);

Now when you try to save a user, the unique validator will check for duplicate database entries and report them just like any other validation error:

var user = new User({ username: 'JohnSmith', email: 'john.smith@gmail.com', password: 'j0hnNYb0i' });
user.save(function (err) {
    console.log(err);
});
{
    message: 'Validation failed',
    name: 'ValidationError',
    errors: {
        username: {
            message: 'Error, expected `username` to be unique. Value: `JohnSmith`',
            name: 'ValidatorError',
            kind: 'unique',
            path: 'username',
            value: 'JohnSmith'
        }
    }
}

When using findOneAndUpdate and related methods, mongoose doesn't automatically run validation. To trigger this, you need to pass a configuration object. For technical reasons, this plugin requires that you also set the context option to query.

{ runValidators: true, context: 'query' }

A full example:

User.findOneAndUpdate(
    { email: 'old-email@example.com' },
    { email: 'new-email@example.com' },
    { runValidators: true, context: 'query' },
    function(err) {
        // ... 
    }
)

You can pass through a custom error type as part of the optional options argument:

userSchema.plugin(uniqueValidator, { type: 'mongoose-unique-validator' });

After running the above example the output will be:

{
    message: 'Validation failed',
    name: 'ValidationError',
    errors: {
        username: {
            message: 'Error, expected `username` to be unique. Value: `JohnSmith`',
            name: 'ValidatorError',
            kind: 'mongoose-unique-validator',
            path: 'username',
            value: 'JohnSmith'
        }
    }
}

You can pass through a custom error message as part of the optional options argument:

userSchema.plugin(uniqueValidator, { message: 'Error, expected {PATH} to be unique.' });

You have access to all of the standard Mongoose error message templating:

  • {PATH}
  • {VALUE}
  • {TYPE}

For case-insensitive matches, include the uniqueCaseInsensitive option in your schema. Queries will treat john.smith@gmail.com and John.Smith@gmail.com as duplicates.

var userSchema = mongoose.Schema({
    username: { type: String, required: true, unique: true },
    email: { type: String, index: true, unique: true, required: true, uniqueCaseInsensitive: true },
    password: { type: String, required: true }
});

Because we rely on async operations to verify whether a document exists in the database, it's possible for two queries to execute at the same time, both get 0 back, and then both insert into MongoDB.

Outside of automatically locking the collection or forcing a single connection, there's no real solution.

For most of our users this won't be a problem, but is an edge case to be aware of.