Loopback: Hooks: Unable to delete a context.instance property

[PuKoren]

I try to clean up some data after processing it into my context object, using:

Let's say ctx.instance contains the following:

{
  unwantedField: "MY_SUPER_MESSAGE",
  something: "ok",
  anotherThing: "not ok"
}

MyModel.observe('before save', function doSomethingOnDB(ctx, next) {
  if (ctx.instance) {
    //do something on insert, like filling another DB or calling a webservice
    //then delete not wanted properties so they are not stored in my DB
    ctx.instance.unwantedField = undefined;
    //tried delete either
    delete ctx.instance.unwantedField;
  }
  next();
});

But it appears that ctx.instance.unwantedField is stored in my DB anyway with value "MY_SUPER_MESSAGE"
Setting it to null insert it with null value, but I have no way to completely remove it and prevent insertion into the database.

[bajtos]

@PuKoren thank you for reporting the issue. What model method is triggering your "before save" hook? Could you please provide us a full code to reproduce the problem, e.g. as described in https://github.com/strongloop/loopback/wiki/Reporting-issues?

[PuKoren]

Thanks for your answer, the method triggering the hook is the simple built-in POST method.
I'll create the repo asap

[PuKoren]

There is the repo:
https://github.com/PuKoren/loopback-sandbox

Steps to reproduce:

• Clone the repo and start the server
• POST on /MyModels with the following body
  {"WantedProperty": "My Value", "UnwantedProperty": "Value 2"}
• GET on /MyModels and see the result (UnwantedProperty is still there)

[fabien]

This is a known issue - it's why unsetAttribute exists. Try it instead of delete ctx.instance.unwantedField; like this:

ctx.instance.unsetAttribute('unwantedField');

[PuKoren]

This works, thanks.

[fabien]

@crandmck perhaps unsetAttribute should be more clearly documented somewhere. The reason why delete inst.prop doesn't work, is because of the internal object that stores the actual attribute values.

[crandmck]

Added to http://docs.strongloop.com/display/LB/Operation+hooks#Operationhooks-Operationhookcontextobject. Thanks for the heads up!
BTW, this is an area where we want to improve the docs in general - see #1173.

[fabien]

@crandmck actually, it's not tied to operation hooks at all. In general, if you ever want to remove a property from a model instance, this is the way to do it. So I think it should move up to a more basic level of the docs (working with models?).

[crandmck]

Oh, ok; thanks. My assumption was based on the example code above. How do you get the ctx object? Can you provide an example of using this outside of a hook?

[fabien]

@crandmck sure:

var inst = new Thing({ foo: 'bar' });
inst.unsetAttribute('foo');
console.log(inst.foo);  // undefined
console.log(inst.toObject()); // {}

[afilp]

Is unsetAttribute deprecated? I cannot see it in loopback v3.