Replace the built-in ORM with another package

[jeff3yan]

I've been working around the limitations for loopback when attempting to query based on related model properties (e.g. Customer belongsTo City belongsTo Country, then trying to query all customers in "Portland").

This issue has been brought up in #517, #683 and many others. However, I'm not sure what the status is on any recommended workarounds besides writing native SQL.

To that point it would be convenient if I could replace the loopback ORM with another package (maybe objection.js or something backed by knex.js) which can filter on related properties.

There was this question relating to providing the loopback datasource connection to use in knex, but it didn't get anywhere.

Is there any way I could incrementally remove the reliance on the built-in ORM and replace it with something else?

[bajtos]

My recommendation is to use plain models (based on Model, not PersistedModel) as controllers, and then implement any data-access methods as custom model (controller) methods backed by whatever ORM you prefer.

// common/models/CustomerController.json
{
  "name": "CustomerController",
  "base": "Model",
  "methods": {
    "find": {
      "accepts": // ...
      "returns": // ...
    }
  }
}

// common/models/CustomerController.js
module.exports = function(CustomerController) {
  CustomerController.find = function(...) {
    return knex(...);
  };
}

We are working on making Controllers a first-class concept in https://github.com/strongloop/loopback-next.