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? Is this a scala bug?
- Sean Reque
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