Hi,
Here's another example.
{"lotto":
{
"id": 5,
"winning-numbers": [2,45,34,23,7,5,3],
"draw-date": "2009-09-14T18:00:00Z",
"winners": [
{"winner-id": 23, "numbers": [2,45,34,23,3,5] },
{"winner-id": 54, "numbers":[52,3,12,11,18,22] }
]
}
}
At the moment I'm extracting this with following case class structure.
case class Winner(@path("winner-id") id: Long, numbers: List[Int])
case class Lotto(id: Long, @path("winning-numbers") winningNumbers:
List[Int], winners: List[Winner],
@path("draw-date") drawDate: Option[Date])
Using a trait approach it would be something like:
case class Winner(id: Long with WinnerIdNominator, numbers: List[Int])
case class Lotto(id: Long, winningNumbers: List[Int] with
WinningNumbersNominator, winners: List[Winner],
drawDate: Option[Date] with DrawDateNominator)
trait WinnerIdNominator extends Nominator {
def name = "winner-id"
}
trait WinningNumbersNominator extends Nominator {
def name = "winning-numbers"
}
trait DrawDateNominator extends Nominator {
def name = "draw-date"
}
Now, there's some problems.
1. Mixin a trait with a primitive fails:
scala> case class Winner(id: Long with WinnerIdNominator, numbers: List
[Int])
<console>:5: error: ambiguous reference to overloaded definition,
both method == in class Object of type (AnyRef)Boolean
and method == in class Long of type (Long)Boolean
match argument types (Long with WinnerIdNominator)
case class Winner(id: Long with WinnerIdNominator, numbers: List
[Int])
2. How to get access to Nominator.name using reflection?
When extracting values we have json and type of target instance, in
this example classOf[Lotto]. It is not clear to me how those traits
should be reflected at runtime.
Cheers Joni
On Sep 14, 1:31 am, "marius d." <marius.dan...@gmail.com> wrote:
> On Sep 13, 3:15 pm, Joni Freeman <freeman.j...@gmail.com> wrote:
>
>
>
> > Hi,
>
> > That annotation is used to configure the json path when extracting
> > values. By default the extraction code assumes that case class
> > parameter names match with json field names. For instance these match:
>
> > case class Foo(bar: String, baz: Int)
> > { "bar": "qwerty", "baz": 10 }
>
> > But sometimes json field names can contain characters which are not
> > allowed in Scala identifiers. For example:
> > { "foo-bar": "qwerty", "baz": 10 }
>
> > Now, to able to extract this we have to somehow tell the extractor the
> > exact path explicitly. Currently @path annotation is used for that:
> > case class Foo(@path("foo-bar") bar: String, baz: Int)
>
> > I don't see how a trait can accomplish this, maybe I'm missing
> > something?
>
> > The reason why it is in Java is that Scala annotations are not
> > accessible at runtime.
>
> Right but I'd also suggest removing Java code from Lift stack. The
> above can be easily achieved by introducing a trait such as:
>
> case class Foo(bar: String with Nominator, baz: Int)
>
> Lift is a 100% Scala code with zero Java code. We also have strong
> opinions in the team that we should stay away from annotations.
>
> one option would be something like this:
>
> Lift would have :
>
> trait Nominator{
> def name : String
>
> }
>
> In user's code:
>
> case class Foo(bar: String with MyNominator, baz: Int)
>
> trait MyNominator extends Nominator {
> def name = "foo-bar"
>
> }
>
> Yes it is more verbose then the annotation but IMHO it is more Scala-
> ish & Lift-ish.
>
>
>
> > Cheers Joni
>
> > On Sep 13, 11:03 pm, Timothy Perrett <timo...@getintheloop.eu> wrote:
>
> > > Just had a browse over the latest commit and found the following in
> > > path.java:
>
> > > @Retention(RetentionPolicy.RUNTIME)
> > > @Target(ElementType.TYPE)
> > > public @interface path {
> > > public String value();
>
> > > }
>
> > > Any reason were not using a trait etc to complete the same
> > > functionality?
>
> > > Cheers, Tim
>
>
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