Or provide a default: after map(...is).openOr("").
You can even do openOr(Predef.error("...")) etc. Note that Predef is necessary
if you imported S.error or S._.
-------------------------------------
Ross Mellgren<dri...@gmail.com> wrote:
I'm not too familiar with mapper, but the probable reason it's giving
back a box is in case the target object cannot be resolved (e.g. the
FK is NULL, or something). Box can either contain a single object or
is empty. In this case you need to pick what to do with an empty box,
and there are a couple approaches in your situation:
1) Use map to make your venueName function return a Box of String,
Empty if the venue could not be found, or Full of the venuename if it
could. This is probably the best bet.
def venueName = venue.obj.map(_.venuename.is)
then calling code either continues to map along, or uses pattern
matching to extract:
event.venueName match {
case Full(name) => do something with the name
case _ => do something when the name cannot be found
}
2) Take a function to apply to the venueName if it could be found.
This is a bit contrived, you'd probably just use approach 1 and map
the box:
def withVenueName(f: String => Unit) = venue.obj.foreach(venue =>
f(venue.venuename.is))
which is equivalent to doing approach 1 with a map or foreach, like
this:
event.venueName.foreach { name => println(name) }
3) just open the box, forcefully. This causes an exception if the box
is empty, and is usually a bad idea:
def venueName = venue.obj.open_!.venuename.is
Hope that helps,
-Ross
On Jul 26, 2009, at 6:29 PM, Grant Wood wrote:
>
> I'm having a frustrating time trying to access an entity using a
> MappedLongForeignKey based on the example I found in section 6.1.4. of
> the Master.PDF. This seems like it should be trivial to do, however I
> cannot compile code which appears to be functionally identical to the
> example provided. Perhaps the document is out of date or someone with
> more experience with Lift can point me in the right direction.
>
> The documentation (master.pdf section 6.1.4 using listing 6.9) states:
> " ... Once we have this defined, accessing the object via the
> relationship is achieved by using the obj method on the foreign key
> field. ..."
>
> Attempting this myself generates a compile error:
> ... /Event.scala:23: error: value venuename is not a member of
> net.liftweb.util.Box[com.subtlesol.model.Location]
>
> (See code fragments below)
>
> venu.obj is returning a Box object, not the Location object I am
> expecting... so clearly it would not be able to access the member
> "venu.obj.venuename" from the Location as the given example would
> suggest. I understand the compile error, but do not see how to apply
> the example to what I am doing. What am I missing?
>
>
> My Code:
>
> class Event extends LongKeyedMapper[Event] with IdPK { ...
> object venue extends MappedLongForeignKey(this, Location)
> def venueName = venue.obj.venuename.is // throws compile error on
> this line
> ... }
>
> class Location extends LongKeyedMapper[Location] with IdPK { ...
> object venuename extends MappedPoliteString(this, 40);
> ... }
>
> Thank You in advance for your help.
>
> >
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