Inheriting Remote Hooks

[wtfribley]

I have two models:

/common/models/parent.json

{
  "name": "Parent",
  "base": "PersistedModel",
  "properties": {},
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": []
}

/common/models/parent.js

module.exports = function(Parent) {
  Parent.afterRemote('**', function(ctx, result, next) {
    console.log('after remote ', ctx.methodString);
    next();
  });
};

/common/models/child.json

{
  "name": "Child",
  "base": "Parent",
  "properties": {},
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": []
}

I would expect that the Parent's afterRemote hook is invoked when any of the Child's remote methods are called -- i.e. that hooks are inherited. Should I not expect this? Is there an alternate way for models to share hooks?

[violet-day]

I have the same question like u.But it's beforeCreate.Child will inherit Parent hook.

[bajtos]

I am afraid this is a limitation of the current implementation of remoting hooks:

ModelCtor.afterRemote = function (name, fn) {
  // ...
      var className = self.modelName;
      remotes.after(className + '.' + name, function (ctx, next) {
        fn(ctx, ctx.result, next);
      });
  // ...

A workaround is to configure the hooks inside the setup function, which is called whenever the model is extended.

/common/models/parent.js

module.exports = function(Parent) {
  Parent.setup = function() {
    Parent.base.setup.apply(this, arguments);

    this.afterRemote('**', function(ctx, result, next) {
      console.log('after remote ', ctx.methodString);
      next();
    });
  };

  Parent.setup();
};

[rus0000]

Seems same with a remoteMethod as well. It only works if defined inside overloaded setup method in parent model.

@bajtos Some questions about example:
/common/models/parent.js
1.
Parent.base.apply(this, arguments); - doesn't work
Parent.base.setup.apply(this, arguments); - works

Why need to call Parent.setup(); if it is

called whenever the model is extended

[bajtos]

ad 1) Good catch, I have updated my comment above. It was a typo on my side.

ad 2) IIRC, loopback calls only one setup method. Consider the following inheritance hierarchy: Model -> PersistedModel -> YourBase -> YourModel. When YourModel is created, loopback will call YourBase.setup and it's up to that method to call PersistedModel.setup.

[rus0000]

2. Sorry for annoyance. It's still not clear to me.
   In our example we have inheritance chain: Model -> PersistedModel -> Parent -> Child

Loopback calls Child.setup, which is probably missing, therefore Parent.setup is invoked by searching prototype chain, as we have defined it with Parent.setup = function() { ... .
In Parent.setup we call base class method with Parent.base.setup.apply(this, arguments); which is defined in PersistedModel.setup. That's fine.

But why there is a call of Parent.setup(); at the end of an example. Why to call itself immediately after definition?

[bajtos]

But why there is a call of Parent.setup(); at the end of an example. Why to call itself immediately after definition?

AFAIK, LoopBack does not call setup function when a new model is defined. In other words, if your Child model provides a setup function, it is called only when somebody extends (inherits from) your Child, but not when the Child is defined as a standalone model. See #550.

Sorry for annoyance. It's still not clear to me.

No worries, I am happy to explain. Is there anything else to explain in order to make this matter more clear?

[rus0000]

OK. We provide setup function for Parent. It is called by Loopback when the Parent is extended. But why need to call it explicitly in a moment of definition?

[bajtos]

But why need to call it explicitly in a moment of definition?

Because if you do not call it explicitly, then it won't be called for your leaf (non-base) model. You can verify this yourself by adding the following Car model to your app:

// common/models/car.json
{
  "name": "Car"
}

// common/models/car.js
module.exports = function(Car) {
  Car.setup = function() {
    console.log('setup');
  };
};

// server/model-config.json
{
  "Car": {
    "dataSource": "db" 
  }
}

[bajtos]

/cc @davidcheung you were investigating model inheritance recently. I think the conclusion was that we should prefer users to put stuff-to-be-inherited in the setup() method instead of auto(magic) inheritance. What do you think about this particular use case?

[davidcheung]

@bajtos yeah that was the conclusion (more info)
I was testing it the other day and couldn't reach my use case, I think the very last child will need to recursively call their parents constructor, but from the base -> child direction, but that isnt the behavior
I need to do a little more investigation into this issue but yes I think we shouldn't do both inherit AND build.

[bajtos]

LoopBack version 3 is in LTS, we won't be making breaking changes like this one.

[itsdun1]

does setup() inheritence also works with afterRemoteError()