In your use case it can only be Long and User. But there has to be a type
parameter because other people might have a String key and a Request mapper.
And the contents of ManyToMany have to be type safe to enforce their
consistency with however the user of ManyToMany wants them to use it.So I
think what you want is that the compiler should figure out that since you're
using it with a KeyedMapper[Long, User], which is ManyToMany's T <:
KeyedMapper[K,T], and ManyToMany extends KeyedMapper[K,T] and it has a self
type of T, and therefore it would be a compiler error to write anything
besides Long and User, therefore you must want to use Long and User and they
should be inferred.
I could certainly hear that, although I'm not much of a type theorist. So
feel free to open an enhancement ticket on Scala's Trac! :)
If I understood correctly...
On Thu, Aug 6, 2009 at 12:43 PM, glenn <gl...@exmbly.com> wrote:
>
> Naftoli,
>
> As I said at the outset, this is really beyond my expertise. But I
> think it's too
> broad and maybe, even unnecessary. In my example, K can only be one
> type,
> Long, and T can only be of type User. Anything else, and the compiler
> can't be
> guaranteed to catch it, but try running the application and you get
> things like
> stack overflow errors.
>
> How you would fix this is beyond me. All you can really do, at this
> point, is
> make sure to include these kinds of restrictions in the docs.
>
> Glenn...
>
> On Aug 6, 9:33 am, Naftoli Gugenheim <naftoli...@gmail.com> wrote:
> > It's too broad, or it's too restrictive/unnecessary? I'm confused, you
> seem
> > to imply both.If it's too broad, tell me why. But if you want to know why
> it
> > needs the type parameter, it's because it has to use the type parameter
> in
> > its implentation -- just count how many times its source code uses it!
> And
> > if you want to know why the compiler can't infer it or be told to infer
> > it... that's another issue.
> > But if passing a type that creates a conflicting inheritance causes a
> > compiler crash, that's not something I can help. :)
> > Regards.
> >
> > On Thu, Aug 6, 2009 at 12:26 PM, glenn <gl...@exmbly.com> wrote:
> >
> > > Naftoli,
> >
> > > At the risk of discussing something obviously beyond my pay grade,
> > > isn't the real issue Scala traits
> > > and the use of parameterized types. The ManyToMany trait is defined
> > > as:
> >
> > > trait ManyToMany[K,T<:KeyedMapper[K, T]]....
> >
> > > But this isn't really correct,is it, the parameter is too broad, and
> > > that leads to a lot of the confusion and results in the need for
> > > unnecessary documentation. When you think about it, why all the
> > > duplication? Why do I need to
> > > write my User entity as:
> >
> > > class User extends MegaProtoUser[User] with ManyToMany[Long,User]
> >
> > > when we all know that this would be much cleaner:
> >
> > > class User extends MegaProtoUser[User] with ManyToMany.
> >
> > > But traits aren't like interfaces. They have implementation and would
> > > need to know something about
> > > the parent class they are attached to - and how would you accomplish
> > > that (reflection, maybe). This is
> > > more a Scala issue than a Lift one, I think.
> >
> > > Glenn...
> >
> > > On Aug 5, 8:24 pm, Naftoli Gugenheim <naftoli...@gmail.com> wrote:
> > > > Building causes a stack overflow?
> > > > So the question is, is it the resident compiler or plain scalac also
> > > crashes? Or just the presentation compiler? What do you see in the
> error log
> > > view or file?
> > > > I get compiler crashes very often when doing fancy mapper type
> related
> > > tricks.
> >
> > > > -------------------------------------
> >
> > > > glenn<gl...@exmbly.com> wrote:
> >
> > > > Naftoli,
> >
> > > > Hate to do this to you, but I'm getting the following error using
> > > > ManyToMany for Users to Roles:
> >
> > > > Message: java.lang.RuntimeException: Broken join
> > > > scala.Predef$.error(Predef.scala:76)
> >
> > > net.liftweb.mapper.ManyToMany$MappedManyToMany$$anonfun$children$1$
> > > > $anonfun$apply$1.apply(ManyToMany.scala:54)
> >
> > > net.liftweb.mapper.ManyToMany$MappedManyToMany$$anonfun$children$1$
> > > > $anonfun$apply$1.apply(ManyToMany.scala:54)
> > > > net.liftweb.util.EmptyBox.openOr(Box.scala:372)
> > > >
> net.liftweb.mapper.ManyToMany$MappedManyToMany$$anonfun$children
> > > > $1.apply(ManyToMany.scala:54)
> > > >
> net.liftweb.mapper.ManyToMany$MappedManyToMany$$anonfun$children
> > > > $1.apply(ManyToMany.scala:54)
> > > > scala.List.map(List.scala:812)
> > > > net.liftweb.mapper.ManyToMany$MappedManyToMany.children
> > > > (ManyToMany.scala:54)
> > > > net.liftweb.mapper.ManyToMany$MappedManyToMany.elements
> > > > (ManyToMany.scala:96)
> > > > scala.Seq$class.flatMap(Seq.scala:293)
> > > > net.liftweb.mapper.ManyToMany$MappedManyToMany.flatMap
> > > > (ManyToMany.scala:44)
> >
> > > > def edit(ns: NodeSeq): NodeSeq = {
> > > > val theUser = view.entity
> > > > val addRole = TheBindParam("insert", view.snippet.link("edit", ()
> > > > => theUser.roles += new Role, Text(S?("Add Role"))))
> >
> > > > bind("user", ns,
> > > > "firstname" -> text(theUser.firstName.is, theUser.firstName
> > > > (_), ("size","20")),
> > > > "lastname" -> text(theUser.lastName.is,theUser.lastName(_),
> > > > ("size", "30")),
> > > > "roles" -> theUser.roles.flatMap{role =>
> > > > bind("role", ns,
> > > > "name" -> role.name.toForm,
> > > > "remove" -> SHtml.submit(S?("Remove"), ()=>
> > > > theUser.roles -= role)
> > > > )
> > > > },
> > > > addRole,
> > > > "submit" -> SHtml.submit(S?("Save"), ()=>view.save)
> > > > )
> > > > }
> >
> > > > The offending code seems to be the line: "roles" ->
> > > > theUser.roles.flatMap{....
> > > > in the above bind method when I click on the addRole link.
> >
> > > > Here's my User class:
> >
> > > > class User extends MegaProtoUser[User] with ManyToMany[Long,User]{
> > > > def getSingleton = User // what's the "meta" server
> >
> > > > object roles
> > > > extends MappedManyToMany(UserRole, UserRole.user, UserRole.role,
> > > > Role)
> >
> > > > }
> >
> > > > What am I doing wrong? You can see how difficult it is to slog
> through
> > > > this code, let alone just
> > > > trying to explain the problem so I can get help.
> >
> > > > On Aug 5, 9:57 am, Naftoli Gugenheim <naftoli...@gmail.com> wrote:
> >
> > > > > I'll try.
> > > > > By the way, as per my correction, you can implement list the
> regular
> > > way without ModelView, and just use ModelSnippet's load function in
> your
> > > edit link or button, passing it the User instance.
> >
> > > > > -------------------------------------
> >
> > > > > glenn<gl...@exmbly.com> wrote:
> >
> > > > > Naftoli,
> >
> > > > > I fixed my code per your comments and now I can edit and remove
> users
> > > > > from a list, as long as I populate the list with
> > > > > ModelView instances, as you said. As for the docs, this step was
> not
> > > > > clear to me at all. I just assumed that the list was
> > > > > just populated with User entities and the view in the ModelSnippet
> was
> > > > > instantiated with the selected User on each request.
> >
> > > > > It sounds like your plate is pretty full, so I won't expect much,
> but
> > > > > sometime soon, could you provide an example, or improved
> > > > > docs, for using TableEditor and its related ItemsList trait.
> >
> > > > > Thanks for all.
> >
> > > > > Glenn...
> >
> > > > > On Aug 5, 9:18 am, Naftoli Gugenheim <naftoli...@gmail.com> wrote:
> >
> > > > > > Correction: ModelSnippet.load takes the actual Mapper instance,
> not
> > > the ModelView wrapper.
> >
> > > > > > -------------------------------------
> >
> > > > > > Naftoli Gugenheim<naftoli...@gmail.com> wrote:
> >
> > > > > > To answer your immediate question, the listing should not refer
> to
> > > the snippet's view but new ModelView instances for each entity. Then
> > > editAction is shorthand for the snippet's link method with a callback
> to
> > > call load on the ModelView. To set the snippet's view's entity, either
> call
> > > load on the snippet with the other ModelView, or call load on the other
> > > ModelView (or just set its entity directly).
> > > > > > As far as documentation, please tell me what scaladocs need what
> > > clarification. Thanks.
> >
> > > > > > -------------------------------------
> >
> > > > > > glenn<gl...@exmbly.com> wrote:
> >
> > > > > > Naftoli,
> >
> > > > > > Functional programming systems are notoriously difficult to
> document.
> > > > > > The only way to really know what's going on is to meticulously
> trace
> > > > > > through the source. But that requires
> > > > > > time-consuming trial and error coding. So, without clear examples
> > > > > > demonstrating exactly what you have in mind, I and others in the
> same
> > > > > > boat, could spend days and still not
> > > > > > get it right.
> >
> > > > > > For example, I tried this:
> >
> > > > > > var theUser:User = null
> > > > > > val view = new ModelView(theUser, this)
> >
> > > > > > def list(ns: NodeSeq): NodeSeq = User.currentUser.map({user =>
> > > > > > User.findAll.flatMap({u =>
> > > > > > bind("user", chooseTemplate("user", "entry", ns),
> > > > > > "firstname" -> Text(u.firstName.is),
> > > > > > "lastname" -> Text(u.lastName.is),
> > > > > > "email" -> Text(u.email.is),
> > > > > > "roles" ->
> u.roles.map(_.name.toString).mkString(",
> > > > > > "),
> > > > > > view.editAction,
> > > > > > view.removeAction
> > > > > > )
> > > > > > })
> > > > > > }) openOr Text("You're not logged in")
> >
> > > > > > and, I get a null value exception when I try to remove a user in
> the
> > > > > > list. Simply using
> > > > > > val view = new ModelView(new User, this), doesn't work either,
> > > > > > although I don't get an
> > > > > > exception. Now, where should I be calling load in all of this?
> >
> > > > > > Glenn...
> >
> > > > > > On Aug 3, 6:22 pm, Naftoli Gugenheim <naftoli...@gmail.com>
> wrote:
> >
> > > > > > > Your snippet should extend ModelSnippet (which extends
> > > StatefulSnippet).
> > > > > > > Then write:
> > > > > > > val view = new ModelView(new User, this) {}
> > > > > > > Calling load on another ModelView that references the snippet
> will
> > > load its entity into that view val. It has a number of methods of
> possible
> > > interest, like save which checks validity.
> > > > > > > Also see Util.
> > > > > > > Are you seeing the scaladocs?
> >
> > > > > > > -------------------------------------
> >
> > > > > > > glenn<gl...@exmbly.com> wrote:
> >
> > > > > > > Just to add to what I just wrote, I don't see how your
> ModelView
> > > can
> > > > > > > be applied to
> > > > > > > User, which already extends a class, MegaProtoUser. Maybe I'm
> not
> > > > > > > comprehending this correctly.
> >
> > > > > > > Glenn...
> >
> > > > > > > On Aug 3, 3:48 pm, glenn <gl...@exmbly.com> wrote:
> >
> > > > > > > > Naftoli,
> >
> > > > > > > > Liked your OneToMany article, but not sure how the new
> > > > > > > > ModelView and ModelSnippet code can be applied to ManyToMany.
> > > > > > > > Can you provide a sample?
> >
> > > > > > > > Glenn...
> >
> > > > > > > > On Aug 2, 1:21 pm, Naftoli Gugenheim <naftoli...@gmail.com>
> > > wrote:
> >
> > > > > > > > > I put an article on the wiki about OneToMany --
> > >http://wiki.github.com/dpp/liftweb/how-to-work-with-one-to-many-relat.
> ..
> > > > > > > > > .
> >
> > > > > > > > > On Sun, Aug 2, 2009 at 11:20 AM, Naftoli Gugenheim <
> > > naftoli...@gmail.com>wrote:
> >
> > > > > > > > > > Glad to hear. Also see mapper.view.ItemsList (anyone have
> a
> > > better name?),
> > > > > > > > > > which is used byTableEditor. It's a similar idea without
> > > relationships.
> >
> > ...
> >
> > read more ยป
> >
>
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