Using Guice in a method that builds something using "this"

[adrien....@live.fr]

Hello all.

Lets say I have:

class A {
//...
}

class B {
    A getA() {
        // Building a A using B attributes
    }
//...
}

I'd love to write:

class B {
    private final a;

    @Inject
    private B(A a) {
        this.a = a;
    }
//...
}

But, since the building of the A instance relies on some data from B, I can not.
Typical exemple would be two classes mapping two SQL tables, where getA() is following a foreign key.

Is there a way Guice can be used around here? (Factory that uses "this", something like that)
Perhaps is it a silly question, and I should do my "new" thing as I would if Guice wasn't around; but it is, so I'm trying to find the proper answer here.


Adrien.

[Stephan Classen]

The thing you are looking for is called assisted injection.
https://github.com/google/guice/wiki/AssistedInject

But often when you need to pass runtime values to an object created with guice. The object is a mix between a data structure and a business object. Try to separate them and the assisted injection becomes unnecessarry.

[Tim Boudreau]

What you have is a design problem.  If A needs B to exist, and B needs A to exist, then either

 - There is some other implicit object that provides data to both A and B, or

 - You really have one logical class, and your implementation is trying to pretend it's two

The most straightforward way to resolve this is don't use Guice to construct these.  I.e. A constructs a B and passes "this" to it and stores it as a field.  Done.

Or if you want to use Guice to construct it (and arguably a better design), have

@Inject

A (AandBData data) {...}

...

@Inject

B (AandBData data) {...}

-Tim

[Stephan Classen]

If I read the example correctly. B does not need A. It just provides a method to retrieve a new instance of A.

So A and B should really be 2 separate classes.