I am working on generic data-access library (for example for accessing your SQL database) inspired b...

# announcements

[diesieben07]

I am working on generic data-access library (for example for accessing your SQL database) inspired by the great model system in Django (Python).
The general idea is that you write your database models like this:

object UserModel : Model {
    val name by VarcharField()
}

From that I am doing to generate code like this (using an annotation processor):
data class User(val name: String)

If I now have a call like dataSource.findAll(UserModel) how can I express to the compiler that this returns List<User>?

[Pavlo Liapota]

https://pl.kotl.in/Hkknfl6dN

[diesieben07]

Well, yes. But User is generated by an annotation processor.

[Pavlo Liapota]

Also look at QueryDSL http://www.querydsl.com/static/querydsl/4.1.3/reference/html_single/#d0e211
They do this other way around: generate model class based on annotations on entity class.

[diesieben07]

Yes, I have used QueryDSL in the past. Even if I do it the other way around there is still no way to "connect" the data class and the Model object.
That would make thinks like this impossible:
findAll<User> { it.name eq "Peter" } where it has to be UserModel, not User

[diesieben07]

Maybe what I want is not possible...

[Pavlo Liapota]

but this would be possible

findAll(UserModel) { it.name eq "Peter" }

looks almost the same 🙂

[diesieben07]

Hm. True. I'll take a stab at that later when I'm back home. Thank you!

[diesieben07]

One issue with using annotations is that it gives reduced type safety.
@Varchar val name: Int is not a compile-time error, even though it should be.