[Lift] Re: Help with writing generic functions for lift mapper
On Fri, Jun 19, 2009 at 6:35 AM, Sean Reque seanre...@gmail.com wrote:
I am trying to write a generic function to do a on-to-one join between
mapper objects in memory using a map. The function is as follows:
def oneToOneJoin[PType : LongKeyedMapper[PType] with IdPK,
CType : LongKeyedMapper[CType] with IdPK,
CMetaType : CType with LongKeyedMetaMapper
[CType],
FKType : MappedLongForeignKey[PType, CType]]
(parents: List[PType], metaMapper: CMetaType, keyGetter: (PType) =
FKType ):
Map[Long, CType] = {
(Map.empty[Long, CType] /: metaMapper.findAll(
ByList(metaMapper.id, parents.map {p = keyGetter
(p).is.longValue } ))
) {(accum, v) = accum + (v.id.longValue - v) }
This function compiles fine, but I can't use it! Here is the call
site:
Util.oneToOneJoin(runs, TestSubject, (tr: TestRun) = tr.testSubject
where runs is of type List[TestRun]
Here are the relevant class and object definitions. All the
definitions are by the book, meaning the exploring Lift book :).
Each test run has one test subject.
class TestSubject extends LongKeyedMapper[TestSubject] with IdPK {
object TestSubject extends TestSubject with LongKeyedMetaMapper
[TestSubject] {
class TestRun extends LongKeyedMapper[TestRun] with IdPK {
object testSubject extends MappedLongForeignKey(this,
TestSubject)
}
object TestRun extends TestRun with LongKeyedMetaMapper[TestRun]
with CRUDify[Long, TestRun] {
I get an error that makes me think I'm coding in C++ with the boost
library. Scala is inferring CType as Nothing, which is definitely not
what I want.
error: inferred type arguments
[com.test_results.model.TestRun,Nothing,object
com.test_results.model.TestSubject,object
com.test_results.model.TestRun#testSubject] do not conform to method
oneToOneJoin's type parameter bounds [PType :
net.liftweb.mapper.LongKeyedMapper[PType] with
net.liftweb.mapper.IdPK,CType : net.liftweb.mapper.LongKeyedMapper
[CType] with net.liftweb.mapper.IdPK,CMetaType : CType with
net.liftweb.mapper.LongKeyedMetaMapper[CType],FKType :
net.liftweb.mapper.MappedLongForeignKey[PType,CType]]
Util.oneToOneJoin(runs, TestSubject, (tr: TestRun) =
tr.testSubject)
I cannot find any way to get the class of the TestSubject companion
object, So I changed things slightly to create a MetaTestSubject and
then tried to explicitly specify the type parameters to the
oneToOneJoin function as shown below. MetaTestSubject is the supertype
for the TestSubject companion object so that I can reference it's type
explicitly.
Util.oneToOneJoin[TestRun,
TestSubject,
MetaTestSubject,
(TestRun) = MappedLongForeignKey[TestRun,
TestSubject]
](runs, TestSubject, (tr: TestRun) = tr.testSubject)
where MetaTestSubject and TestSubject are now defined as
class MetaTestSubject extends TestSubject with LongKeyedMetaMapper
[TestSubject]
object TestSubject extends MetaTestSubject {
When I specify the types to the oneToOneJoin function explicitly,
Scala then just plain tells me that the types don't match with this
error.
error: type arguments
[com.test_results.model.TestRun,com.test_results.model.TestSubject,com.test_results.model.MetaTestSubject,
(com.test_results.model.TestRun) =
net.liftweb.mapper.MappedLongForeignKey
[com.test_results.model.TestRun,com.test_results.model.TestSubject]]
do not conform to method oneToOneJoin's type parameter bounds [PType
: net.liftweb.mapper.LongKeyedMapper[PType] with
net.liftweb.mapper.IdPK,CType : net.liftweb.mapper.LongKeyedMapper
[CType] with net.liftweb.mapper.IdPK,CMetaType : CType with
net.liftweb.mapper.LongKeyedMetaMapper[CType],FKType :
net.liftweb.mapper.MappedLongForeignKey[PType,CType]]
Util.oneToOneJoin[TestRun,
After a couple of hours of trying I am stuck at this point and all of
the types look like they line up to me. TestRun is a LongKeyedMapper
of the right type with IdPK, and so is TestSubject. MetaTestSubject
inherits from TestSubject with LongKeyedMetaMapper[TestSubject]. The
third value parameter is a function takes a type TestRun and returns a
MappedLongForeignKey[TestRun, TestSubject].
What am I doing wrong?
In the second one where you explicitly specified the types, you are doing
nothing wrong.
In the first case, because there were no parameters with the type CType, the
type inferencer couldn't figure out what CType was. The type inferencer
only looks a certain number of levels for a type in order to avoid cyclical
type references and in order to save compilation speed.
Is this a scala bug?
Yes.
I would suggest reporting it.
- Sean Reque
--
Lift, the simply functional web framework http://liftweb.net
Beginning Scala http://www.apress.com/book/view/1430219890
Follow me: http://twitter.com/dpp
Git some: http://github.com/dpp
--~--~-~--~~~---~--~~
[Lift] Re: Help with writing generic functions for lift mapper
Thanks for the quick response! I will submit a ticket in the scala bug
tracker.
On Jun 19, 10:14 am, David Pollak feeder.of.the.be...@gmail.com
wrote:
On Fri, Jun 19, 2009 at 6:35 AM, Sean Reque seanre...@gmail.com wrote:
I am trying to write a generic function to do a on-to-one join between
mapper objects in memory using a map. The function is as follows:
def oneToOneJoin[PType : LongKeyedMapper[PType] with IdPK,
CType : LongKeyedMapper[CType] with IdPK,
CMetaType : CType with LongKeyedMetaMapper
[CType],
FKType : MappedLongForeignKey[PType, CType]]
(parents: List[PType], metaMapper: CMetaType, keyGetter: (PType) =
FKType ):
Map[Long, CType] = {
(Map.empty[Long, CType] /: metaMapper.findAll(
ByList(metaMapper.id, parents.map {p = keyGetter
(p).is.longValue } ))
) {(accum, v) = accum + (v.id.longValue - v) }
This function compiles fine, but I can't use it! Here is the call
site:
Util.oneToOneJoin(runs, TestSubject, (tr: TestRun) = tr.testSubject
where runs is of type List[TestRun]
Here are the relevant class and object definitions. All the
definitions are by the book, meaning the exploring Lift book :).
Each test run has one test subject.
class TestSubject extends LongKeyedMapper[TestSubject] with IdPK {
object TestSubject extends TestSubject with LongKeyedMetaMapper
[TestSubject] {
class TestRun extends LongKeyedMapper[TestRun] with IdPK {
object testSubject extends MappedLongForeignKey(this,
TestSubject)
}
object TestRun extends TestRun with LongKeyedMetaMapper[TestRun]
with CRUDify[Long, TestRun] {
I get an error that makes me think I'm coding in C++ with the boost
library. Scala is inferring CType as Nothing, which is definitely not
what I want.
error: inferred type arguments
[com.test_results.model.TestRun,Nothing,object
com.test_results.model.TestSubject,object
com.test_results.model.TestRun#testSubject] do not conform to method
oneToOneJoin's type parameter bounds [PType :
net.liftweb.mapper.LongKeyedMapper[PType] with
net.liftweb.mapper.IdPK,CType : net.liftweb.mapper.LongKeyedMapper
[CType] with net.liftweb.mapper.IdPK,CMetaType : CType with
net.liftweb.mapper.LongKeyedMetaMapper[CType],FKType :
net.liftweb.mapper.MappedLongForeignKey[PType,CType]]
Util.oneToOneJoin(runs, TestSubject, (tr: TestRun) =
tr.testSubject)
I cannot find any way to get the class of the TestSubject companion
object, So I changed things slightly to create a MetaTestSubject and
then tried to explicitly specify the type parameters to the
oneToOneJoin function as shown below. MetaTestSubject is the supertype
for the TestSubject companion object so that I can reference it's type
explicitly.
Util.oneToOneJoin[TestRun,
TestSubject,
MetaTestSubject,
(TestRun) = MappedLongForeignKey[TestRun,
TestSubject]
](runs, TestSubject, (tr: TestRun) = tr.testSubject)
where MetaTestSubject and TestSubject are now defined as
class MetaTestSubject extends TestSubject with LongKeyedMetaMapper
[TestSubject]
object TestSubject extends MetaTestSubject {
When I specify the types to the oneToOneJoin function explicitly,
Scala then just plain tells me that the types don't match with this
error.
error: type arguments
[com.test_results.model.TestRun,com.test_results.model.TestSubject,com.test_results.model.MetaTestSubject,
(com.test_results.model.TestRun) =
net.liftweb.mapper.MappedLongForeignKey
[com.test_results.model.TestRun,com.test_results.model.TestSubject]]
do not conform to method oneToOneJoin's type parameter bounds [PType
: net.liftweb.mapper.LongKeyedMapper[PType] with
net.liftweb.mapper.IdPK,CType : net.liftweb.mapper.LongKeyedMapper
[CType] with net.liftweb.mapper.IdPK,CMetaType : CType with
net.liftweb.mapper.LongKeyedMetaMapper[CType],FKType :
net.liftweb.mapper.MappedLongForeignKey[PType,CType]]
Util.oneToOneJoin[TestRun,
After a couple of hours of trying I am stuck at this point and all of
the types look like they line up to me. TestRun is a LongKeyedMapper
of the right type with IdPK, and so is TestSubject. MetaTestSubject
inherits from TestSubject with LongKeyedMetaMapper[TestSubject]. The
third value parameter is a function takes a type TestRun and returns a
MappedLongForeignKey[TestRun, TestSubject].
What am I doing wrong?
In the second one where you explicitly specified the types, you are doing
nothing wrong.
In the first case, because there were no parameters with the type CType, the
type inferencer couldn't figure out what CType was. The type inferencer
only looks a certain number of levels for a type in order to avoid cyclical
type references and in order to save compilation speed.
Is this a scala bug?
Yes.
I would suggest reporting it.
- Sean Reque
--
Lift,
