Make use of constructor arguments when instantiating mapping targets

[gunnarmorling]

Some thoughts:

• Need a way to select the constructor to use if there are several ones
• Properties not covered by the chosen constructor should be populated by setters
• Optionally, the mechanism should take parameterized factory methods into account

[agudian]

What kind of arguments do you mean?

[gunnarmorling]

I'd like to add some kind of support for immutable target types, which take their attribute values through a constructor:

public class Order {
    private final long id;
    private final String name;

    public Order(long id, String name) { ... }
 }

The generated code would then have to invoke this constructor instead of relying on the default constructor and setters. Generally this should be possbible as we can access the parameter names in the annotation processor.

An open question is how to chose a constructor in case there are several. Optionally existing setters could be invoked for attributes not present in the invoked constructor.

[fcamblor]

👍 on this

We could introduce a @Constructor({"id","name"}) annotation allowing to bind mapping to a dedicated constructor, using named parameters (not types which could be ambiguous and less obvious regarding API readability)

WDYT ?

[gunnarmorling]

@fcamblor, yes, that sounds very reasonable. I first thought @ConstructorProperties from the JDK could be re-used, but that lacks the required element type. +1 for using names.

One thing though: I assume it's a common case that there is a default constructor (no args) and one constructor taking the bean properties. It'd be nice to globally configure which one to use in this case without the need to specify @Constructor for each single method.

[pardom-zz]

I would also like to see this, specifically for immutable objects. Any update?