Hi all, I'm trying to port an existing proof-of-concept written in Java, using an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or MongoDB before so its quite a learning curve.
The issue I'm struggling with now is how to implement class inheritance in MongoDB. In my Java domain model I have the following classes: Party Organization extends Party Person extends Party User extends Person
I don't expect to have any trouble modelling these classes in Scala but I don't know how to then map them to Collections and Documents in MongoDB. I have seen a tutorial that describes how the C# driver automatically handles the inheritance for you but there doesn't seem to be any such functionality in the Java/Scala world.
The reason I'm posting this question in a Lift forum is because I expect the eventual solution to have something to do with lift-mongodb- record (at least I would like that to be the case).
Remember that lift-json only support scala case class(and other class with constructor contains all parameter need to be set. It set values by constructor but not setter method)
And I think the record api is not good for inheritance, so you should use lift-mongo or casbah to save and read your converted json objects.
Inheritance with Record is a little tricky, but there are some things you can do, as pointed out in the links in the posts above.
If you'd prefer to use regular case classes then I'd suggest using Casbah/Salat. Lift has MongoDocument, but Casbah/Salat is more than likely a better choice. If you go this route you'll lose all of the features of Record though. In particular, validation and auto form creation/LiftScreen.
Tim
On Dec 5, 5:44 pm, Kevin Stembridge <kevin.stembridge....@gmail.com> wrote:
> Hi all, > I'm trying to port an existing proof-of-concept written in Java, using > an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or > MongoDB before so its quite a learning curve.
> The issue I'm struggling with now is how to implement class > inheritance in MongoDB. In my Java domain model I have the following > classes: > Party > Organization extends Party > Person extends Party > User extends Person
> I don't expect to have any trouble modelling these classes in Scala > but I don't know how to then map them to Collections and Documents in > MongoDB. I have seen a tutorial that describes how the C# driver > automatically handles the inheritance for you but there doesn't seem > to be any such functionality in the Java/Scala world.
> The reason I'm posting this question in a Lift forum is because I > expect the eventual solution to have something to do with lift-mongodb- > record (at least I would like that to be the case).
Thank you all for the advice. Looking at the samples in the suggested
links I realise that I don't know enough Scala to understand them. I
think I might have to focus a bit on the basics of the language
first.
On Dec 6 2011, 4:03 pm, Tim Nelson <t...@eltimn.com> wrote:
> Inheritance with Record is a little tricky, but there are some things
> you can do, as pointed out in the links in the posts above.
> If you'd prefer to use regular case classes then I'd suggest using
> Casbah/Salat. Lift has MongoDocument, but Casbah/Salat is more than
> likely a better choice. If you go this route you'll lose all of the
> features of Record though. In particular, validation and auto form
> creation/LiftScreen.
> Tim
> On Dec 5, 5:44 pm,Kevin Stembridge<kevin.stembridge....@gmail.com>
> wrote:
> > Hi all,
> > I'm trying to port an existing proof-of-concept written in Java, using
> > an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or
> > MongoDB before so its quite a learning curve.
> > The issue I'm struggling with now is how to implement class
> > inheritance in MongoDB. In my Java domain model I have the following
> > classes:
> > Party
> > Organization extends Party
> > Person extends Party
> > User extends Person
> > I don't expect to have any trouble modelling these classes in Scala
> > but I don't know how to then map them to Collections and Documents in
> > MongoDB. I have seen a tutorial that describes how the C# driver
> > automatically handles the inheritance for you but there doesn't seem
> > to be any such functionality in the Java/Scala world.
> > The reason I'm posting this question in a Lift forum is because I
> > expect the eventual solution to have something to do with lift-mongodb-
> > record (at least I would like that to be the case).
I've found some time to have another look at my options for mapping class hierarchies. I checked out Casbah/Salat. But I don't want to give up on Record just yet because of the extra features that come with it.
When you say its a little tricky, does that mean its impossible? I've been having a look at the implementation and I think there might be some things I can try. But my first hurdle is some basic scala stuff. I need to create my Record classes first of all but I'm getting errors that are related to type parameterization. I don't know enough Scala to figure out what I need to do to fix the problem. I'm hoping you guys can help.
Here are a couple of my classes:
class PartyRecord extends MongoRecord[PartyRecord] with UUIDPk[PartyRecord] { def meta = PartyRecord object name extends StringField(this, 128)
}
object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
class OrganizationRecord extends PartyRecord { def meta = OrganizationRecord
}
object OrganizationRecord extends OrganizationRecord with MongoMetaRecord[OrganizationRecord]
OrganizationRecord doesn't compile because it expects the meta method to return a PartyRecord. So I believe I need to define PartyRecord so that it is parameterized with an upper bound of PartyRecord. The class below is is the closest I've come so far to getting something that compiles but it complains that the value MyType cannot be found.
class PartyRecord[MyType <:PartyRecord[MyType]] extends MongoRecord[MyType] with UUIDPk[MyType] { self: MyType => def meta = PartyRecord object name extends StringField(this, 128)
}
object PartyRecord extends PartyRecord[MyType] with MongoMetaRecord[PartyRecord[MyType]]
I'm hoping this is just a lack of understanding of how type parameterization works in Scala. Does anyone know what I need to do to get my type hierarchy to compile?
On Monday, 5 December 2011 23:44:01 UTC, Kevin Stembridge wrote:
> Hi all, > I'm trying to port an existing proof-of-concept written in Java, using > an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or > MongoDB before so its quite a learning curve.
> The issue I'm struggling with now is how to implement class > inheritance in MongoDB. In my Java domain model I have the following > classes: > Party > Organization extends Party > Person extends Party > User extends Person
> I don't expect to have any trouble modelling these classes in Scala > but I don't know how to then map them to Collections and Documents in > MongoDB. I have seen a tutorial that describes how the C# driver > automatically handles the inheritance for you but there doesn't seem > to be any such functionality in the Java/Scala world.
> The reason I'm posting this question in a Lift forum is because I > expect the eventual solution to have something to do with lift-mongodb- > record (at least I would like that to be the case).
The problem has more to do with the relationship between MongoRecord and MongoMetaRecord than type hierarchy. I don't think you'll be able to do it the way you're trying here. What you can do is the following:
On Thursday, May 10, 2012 3:27:57 PM UTC-5, Kevin Stembridge wrote:
> I've found some time to have another look at my options for mapping class > hierarchies. I checked out Casbah/Salat. But I don't want to give up on > Record just yet because of the extra features that come with it.
> When you say its a little tricky, does that mean its impossible? I've been > having a look at the implementation and I think there might be some things > I can try. But my first hurdle is some basic scala stuff. I need to create > my Record classes first of all but I'm getting errors that are related to > type parameterization. I don't know enough Scala to figure out what I need > to do to fix the problem. I'm hoping you guys can help.
> Here are a couple of my classes:
> class PartyRecord extends MongoRecord[PartyRecord] with > UUIDPk[PartyRecord] { > def meta = PartyRecord > object name extends StringField(this, 128) > } > object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
> class OrganizationRecord extends PartyRecord { > def meta = OrganizationRecord > } > object OrganizationRecord extends OrganizationRecord with > MongoMetaRecord[OrganizationRecord]
> OrganizationRecord doesn't compile because it expects the meta method to > return a PartyRecord. So I believe I need to define PartyRecord so that it > is parameterized with an upper bound of PartyRecord. > The class below is is the closest I've come so far to getting something > that compiles but it complains that the value MyType cannot be found.
> class PartyRecord[MyType <:PartyRecord[MyType]] extends > MongoRecord[MyType] with UUIDPk[MyType] { > self: MyType => > def meta = PartyRecord > object name extends StringField(this, 128) > } > object PartyRecord extends PartyRecord[MyType] with > MongoMetaRecord[PartyRecord[MyType]]
> I'm hoping this is just a lack of understanding of how type > parameterization works in Scala. Does anyone know what I need to do to get > my type hierarchy to compile?
> Cheers, > Kevin
> On Monday, 5 December 2011 23:44:01 UTC, Kevin Stembridge wrote:
>> Hi all, >> I'm trying to port an existing proof-of-concept written in Java, using >> an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or >> MongoDB before so its quite a learning curve.
>> The issue I'm struggling with now is how to implement class >> inheritance in MongoDB. In my Java domain model I have the following >> classes: >> Party >> Organization extends Party >> Person extends Party >> User extends Person
>> I don't expect to have any trouble modelling these classes in Scala >> but I don't know how to then map them to Collections and Documents in >> MongoDB. I have seen a tutorial that describes how the C# driver >> automatically handles the inheritance for you but there doesn't seem >> to be any such functionality in the Java/Scala world.
>> The reason I'm posting this question in a Lift forum is because I >> expect the eventual solution to have something to do with lift-mongodb- >> record (at least I would like that to be the case).
Hi Tim, Thanks for the response. I was hoping for better news though. My domain model requires concrete classes to extend other concrete classes. e.g. PartyRecord -> PersonRecord -> UserRecord.
On Friday, 11 May 2012 13:19:18 UTC+1, Tim Nelson wrote:
> Hi Kevin,
> The problem has more to do with the relationship between MongoRecord and > MongoMetaRecord than type hierarchy. I don't think you'll be able to do it > the way you're trying here. What you can do is the following:
> class PartyRecord[OwnerType <: PartyRecord[OwnerType]] > extends BaseRecord[OwnerType] { > def meta = PartyRecord > } > object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
> class OrganizationRecord[OwnerType <: OrganizationRecord[OwnerType]] > extends BaseRecord[OwnerType] { > def meta = OrganizationRecord > } > object OrganizationRecord extends OrganizationRecord with > MongoMetaRecord[OrganizationRecord]
> Basically, you can't create a concrete MongoRecord class and then extend > that. You can create a trait and extend that, however.
> Tim
> On Thursday, May 10, 2012 3:27:57 PM UTC-5, Kevin Stembridge wrote:
>> I've found some time to have another look at my options for mapping class >> hierarchies. I checked out Casbah/Salat. But I don't want to give up on >> Record just yet because of the extra features that come with it.
>> When you say its a little tricky, does that mean its impossible? I've >> been having a look at the implementation and I think there might be some >> things I can try. But my first hurdle is some basic scala stuff. I need to >> create my Record classes first of all but I'm getting errors that are >> related to type parameterization. I don't know enough Scala to figure out >> what I need to do to fix the problem. I'm hoping you guys can help.
>> Here are a couple of my classes:
>> class PartyRecord extends MongoRecord[PartyRecord] with >> UUIDPk[PartyRecord] { >> def meta = PartyRecord >> object name extends StringField(this, 128) >> } >> object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
>> class OrganizationRecord extends PartyRecord { >> def meta = OrganizationRecord >> } >> object OrganizationRecord extends OrganizationRecord with >> MongoMetaRecord[OrganizationRecord]
>> OrganizationRecord doesn't compile because it expects the meta method to >> return a PartyRecord. So I believe I need to define PartyRecord so that it >> is parameterized with an upper bound of PartyRecord. >> The class below is is the closest I've come so far to getting something >> that compiles but it complains that the value MyType cannot be found.
>> class PartyRecord[MyType <:PartyRecord[MyType]] extends >> MongoRecord[MyType] with UUIDPk[MyType] { >> self: MyType => >> def meta = PartyRecord >> object name extends StringField(this, 128) >> } >> object PartyRecord extends PartyRecord[MyType] with >> MongoMetaRecord[PartyRecord[MyType]]
>> I'm hoping this is just a lack of understanding of how type >> parameterization works in Scala. Does anyone know what I need to do to get >> my type hierarchy to compile?
>> Cheers, >> Kevin
>> On Monday, 5 December 2011 23:44:01 UTC, Kevin Stembridge wrote:
>>> Hi all, >>> I'm trying to port an existing proof-of-concept written in Java, using >>> an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or >>> MongoDB before so its quite a learning curve.
>>> The issue I'm struggling with now is how to implement class >>> inheritance in MongoDB. In my Java domain model I have the following >>> classes: >>> Party >>> Organization extends Party >>> Person extends Party >>> User extends Person
>>> I don't expect to have any trouble modelling these classes in Scala >>> but I don't know how to then map them to Collections and Documents in >>> MongoDB. I have seen a tutorial that describes how the C# driver >>> automatically handles the inheritance for you but there doesn't seem >>> to be any such functionality in the Java/Scala world.
>>> The reason I'm posting this question in a Lift forum is because I >>> expect the eventual solution to have something to do with lift-mongodb- >>> record (at least I would like that to be the case).
Between traits, overriding collectionName, optional fields and Mongo's schemalessness you can go a long way - or make quite a mess - but it is a bit of a shame that the kind of thing you want isn't easier here. There are lots of advantages to MongoRecord despite the inheritance thing.
On Saturday, May 12, 2012 7:38:39 PM UTC+2, Kevin Stembridge wrote:
> Hi Tim, > Thanks for the response. > I was hoping for better news though. My domain model requires concrete > classes to extend other concrete classes. e.g. PartyRecord -> PersonRecord > -> UserRecord.
> I'm going to have to weigh up the trade-offs.
> Thanks for the advice. > Kevin
> On Friday, 11 May 2012 13:19:18 UTC+1, Tim Nelson wrote:
>> Hi Kevin,
>> The problem has more to do with the relationship between MongoRecord and >> MongoMetaRecord than type hierarchy. I don't think you'll be able to do it >> the way you're trying here. What you can do is the following:
>> object name extends StringField(self, 128) >> }
>> class PartyRecord[OwnerType <: PartyRecord[OwnerType]] >> extends BaseRecord[OwnerType] { >> def meta = PartyRecord >> } >> object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
>> class OrganizationRecord[OwnerType <: OrganizationRecord[OwnerType]] >> extends BaseRecord[OwnerType] { >> def meta = OrganizationRecord >> } >> object OrganizationRecord extends OrganizationRecord with >> MongoMetaRecord[OrganizationRecord]
>> Basically, you can't create a concrete MongoRecord class and then extend >> that. You can create a trait and extend that, however.
>> Tim
>> On Thursday, May 10, 2012 3:27:57 PM UTC-5, Kevin Stembridge wrote:
>>> I've found some time to have another look at my options for mapping >>> class hierarchies. I checked out Casbah/Salat. But I don't want to give up >>> on Record just yet because of the extra features that come with it.
>>> When you say its a little tricky, does that mean its impossible? I've >>> been having a look at the implementation and I think there might be some >>> things I can try. But my first hurdle is some basic scala stuff. I need to >>> create my Record classes first of all but I'm getting errors that are >>> related to type parameterization. I don't know enough Scala to figure out >>> what I need to do to fix the problem. I'm hoping you guys can help.
>>> Here are a couple of my classes:
>>> class PartyRecord extends MongoRecord[PartyRecord] with >>> UUIDPk[PartyRecord] { >>> def meta = PartyRecord >>> object name extends StringField(this, 128) >>> } >>> object PartyRecord extends PartyRecord with MongoMetaRecord[PartyRecord]
>>> class OrganizationRecord extends PartyRecord { >>> def meta = OrganizationRecord >>> } >>> object OrganizationRecord extends OrganizationRecord with >>> MongoMetaRecord[OrganizationRecord]
>>> OrganizationRecord doesn't compile because it expects the meta method to >>> return a PartyRecord. So I believe I need to define PartyRecord so that it >>> is parameterized with an upper bound of PartyRecord. >>> The class below is is the closest I've come so far to getting something >>> that compiles but it complains that the value MyType cannot be found.
>>> class PartyRecord[MyType <:PartyRecord[MyType]] extends >>> MongoRecord[MyType] with UUIDPk[MyType] { >>> self: MyType => >>> def meta = PartyRecord >>> object name extends StringField(this, 128) >>> } >>> object PartyRecord extends PartyRecord[MyType] with >>> MongoMetaRecord[PartyRecord[MyType]]
>>> I'm hoping this is just a lack of understanding of how type >>> parameterization works in Scala. Does anyone know what I need to do to get >>> my type hierarchy to compile?
>>> Cheers, >>> Kevin
>>> On Monday, 5 December 2011 23:44:01 UTC, Kevin Stembridge wrote:
>>>> Hi all, >>>> I'm trying to port an existing proof-of-concept written in Java, using >>>> an RDBMS, to Lift using MongoDB. I've never used Lift, Scala or >>>> MongoDB before so its quite a learning curve.
>>>> The issue I'm struggling with now is how to implement class >>>> inheritance in MongoDB. In my Java domain model I have the following >>>> classes: >>>> Party >>>> Organization extends Party >>>> Person extends Party >>>> User extends Person
>>>> I don't expect to have any trouble modelling these classes in Scala >>>> but I don't know how to then map them to Collections and Documents in >>>> MongoDB. I have seen a tutorial that describes how the C# driver >>>> automatically handles the inheritance for you but there doesn't seem >>>> to be any such functionality in the Java/Scala world.
>>>> The reason I'm posting this question in a Lift forum is because I >>>> expect the eventual solution to have something to do with lift-mongodb- >>>> record (at least I would like that to be the case).
