Ensure unique field value in loopback model

Question

How to ensure uniqueness of a particular field in loopback model. Like below is the model Post, I have a field genericId in it, I want it to be unique in the database, and loopback to through an error, on duplicate key insertion.

{
  "name": "Post",
  "plural": "Post",
  "base": "PersistedModel",
  "properties": {
    "genericId": {
      "type": "string",
      "required":True 
    },
    "moderatedAt": {
      "type": "date"
    }
  },
  "validations": [],
  "acls": [],
  "methods": []
}

I have tried searching there documentation, and other examples but no success. One solution which I can think of is, to create a remoteHook for the create function, and validate this field before inserting, but looking for some other way.

Extol

you can also enforce uniqueness on your database directly – Bruyn

Yes, Strongloop's LoopbackJS documentation is impossibly miserable. – Reeher

Answer 1

Set validation rule in your common/models/post.js

Post.validatesUniquenessOf('genericId');

Mix

Thanks for the solution, but have already got it, sorry forgot to update it here. – Extol

Correct validation docs docs.strongloop.com/display/APIC/Validating+model+data – Apologetic

Only supported connectors: In Memory, Oracle or MongoDB – Apologetic

What if I want to keep combination of fields to be unique? – Spruce

Answer 2

Not sure if it is the better way to achieve uniqueness, but you can find here the docs about indexing your model.

Just add a unique index on the field you want, and voila !

For your model, that would be :

{
  ...
    "genericId": {
      "type": "string",
      "required": True,
      "index": {"unique": true} 
    },
 ...
}

However, if the genericId field is the actual Id of the model, I suggest you declare it as such, so you can use findById method, and also avoid creation of a duplicate id field, which will happen if you don't declare any in your model.

{
  ...
    "genericId": {
      "type": "string", 
      "id": true,       // Ensure uniqueness and avoid another model id field
      "generated": true // Add this if you want Loopback to manage id content for you
    },
 ...
}

Distinctive

Could you expend on "...declare it as such"? Thanks. – Foveola

Note: this is an old post, not sure if its still valid. In the above message, the code expands on the explanation : you declare a field as a model ID by setting the id prop (to true) in the field json definition. – Distinctive

Answer 3

The Lookback v4 solution looks like this:

@model()
export class Client extends Entity {

  @property({
    type: 'string',
    required: true,
    index: {
      unique: true,
    },
  })
  name: string;

}

Then you must update your schema:

npm run migrate

or recreate it:

npm run migrate -- --rebuild

Hooray

Did you update your schema? npm run migrate or npm run migrate -- --rebuild? – Hooray

Not every connector might support this. I checked it for PostgreSQL. MySQL is supported, too, I guess. – Hooray

Thank you Mathias, this is what I've been looking for. Tested in PostgreSQL. Btw, it doesn't send a good error message for the response. The error response now would only be 500. Does any of you have reference for editing that? Thank you! – Kovach

This answer is more elegant and also correct one for Mongo Driver, in my opinion – Auberon