Mapping extra properties on linking table for manytomany relationship?

[matt.d...@gmail.com]

Hi,

Is there any way I can map properties of a relationship to one of the involved entities?

For instance

table Person (
    id int
    name string
    eventId int
)
table Event (
    id int
    eventName string
    someOtherProps string
)
table Person_Event (
    personId int
    eventId int
    isPresent boolean //this is the extra property, notes whether the person is present at the event
    primary key(personId, eventId)
    foreign key(personId) references Person(id)
    foreign key(eventId) reference Event(id)
)

and then have it map so that when I create my EventEntity

object EventEntity extends Entity[Int, SurrogateIntId, Event] {
     val id = key("id") autogenerated (_.id)
     val name = column("eventName") to (_.name)
     val other = column("someOtherProps") to (_.other)
     val isPresent =  ??? //map the extra property on the linked table here
     val persons = manytomanyreverse(PersonEntity) to (_.persons)
...

}

​

[Konstantinos Kougios]

Hi, it can be possible (I think, I haven't got any test case similar to this). But first, what would your domain model classes look like? And you got Person.eventId and Person_Event.eventId, what's up with both those?

--
You received this message because you are subscribed to the Google Groups "mapperdao" group.
To unsubscribe from this group and stop receiving emails from it, send an email to mapperdao+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[matt.d...@gmail.com]

My apologies, I hastily typed out that code and I realize it doesn’t make much sense now :)

First, a description:
Users can attend multiple Events, and Events can contain multiple Users. The relationship between the two is many-to-many. I would like to include extra information about each individual relationship between an Event and a User though — such as whether the User is present at the Event (isPresent)
Here are more domain objects

class User(val id: Int, val email: String, val createdDate: DateTime, val events: Set[Event]) {
}
class Event(val id: Long, val name: String, val eventType: JoinType.Value, val description: EventDetails, val users: Set[User]) {
}

Initially I thought I would like to have an isPresent field for each Event but after doing some research this does not seem possible(and really doesn’t make sense), what I really trying to achieve is described here, Mapping a Join Table with Additional Columns.

[Konstantinos Kougios]

Yes I think having an Event.isPresent doesn't make sense since it couples the Event with a specific User.

So creating an intermediate entity as  described in your link seems to be the best approach as both User and Event should be decoupled from each other.