Unique field validation

refers to https://github.com/adrai/node-cqrs-domain/issues/70, https://github.com/adrai/node-cqrs-domain/issues/91

Hi, I have the similar question: how to make checks for uniqueness in domain? I tried to check it using eventDenormalizer by saving unique values (emails) into VM by listen domain events and then check it in preCondition:

import * as domain from "cqrs-domain";

export = domain.definePreCondition({
    // @ts-ignore
    name: ['createUser', 'updateUser'],
    priority: 1,
    payload: 'payload',
},  (data, aggregate, callback) => {
    const usersRepo = require('../viewBuilders/user/usersCollection');
    usersRepo.findViewModels({email: data.email}, (err, items) => {
        if(items.length){
            callback("Provided email is already exist in our database!");
        } else {
            callback(null);
        }
    });
});

but this way is not atomic, theoretically there can be situation when 2 users can create their accounts with the same emails. How to avoid this?

[nanov]

Having what @adrai said in mind, there are a few patterns you can apply to solve your problem, after you have decided that cqrs/es is suitable for youe user/account management:

• in your case you can set the aggregate id as the email, and give the command a rule that the aggregate does not exists.

• you may take a look on this answer that i gave for similar question - as last resort this is a solution. In your case

[adrai]

Hehe… welcome to the cqrs world… Do not mix domain and eventDenormalizer stuff that way. To solve this you really need 1 aggregate. To make this more efficient when having too much events, there are snapshots.