Slick join two tables and get result of both - scala

Question

I have a Many to Many relationship setup like this:
Person <-> PersonField <-> Field
Now I want to query not only all the fields of a Person (I can do that), but a joined version of PersonField with Field of a Person. (I want to query/retrieve the Information in the Pivot/Intermediate Table "PersonField" as well!)
Person:
case class Person(id: Long, name: String)
{
def fields =
{
person <- Persons.all.filter(_.id === this.id)
field <- person.fields
} yield field
}
class Persons(tag: Tag) extends Table[Person](tag, "persons")
{
def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
def name = column[String]("name")
def * = (id, name) <> (Person.tupled, Person.unapply)
def fields = PersonFields.all.filter(_.personID === id).flatMap(_.fieldFK)
}
object Persons
{
lazy val all = TableQuery[Persons]
}
Field:
case class Field(id: Long, name: String, description: Option[String])
class Fields(tag: Tag) extends Table[Field](tag, "fields")
{
def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
def name = column[String]("name")
def description = column[Option[String]]("description")
def * = (id, name, description) <> (Field.tupled, Field.unapply)
}
object Fields
{
lazy val all = TableQuery[Fields]
}
PersonField:
case class PersonField(id: Long, personID: Long, fieldID: Long, value: String)
// TODO add constraint to make (personID, fieldID) unique
class PersonFields(tag: Tag) extends Table[PersonField](tag, "person_field")
{
def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
def personID = column[Long]("person_id")
def fieldID = column[Long]("field_id")
def value = column[String]("value")
def * = (id, personID, fieldID, value) <> (PersonField.tupled, PersonField.unapply)
def personFK = foreignKey("person_fk", personID, Persons.all)(_.id)
def fieldFK = foreignKey("field_fk", fieldID, Fields.all)(_.id)
}
object PersonFields
{
lazy val all = TableQuery[PersonFields]
}
Now to query all the fields of a Person I have a little helper-class:
def getFields(p: Person): Future[Seq[Field]] =
{
val query = p.fields
db.run(query.result)
}
So I can do
val personX ...
personX.onSuccess
{
case p: Person =>
{
val fields = helper.getFields(p)
fields.onSuccess
{
case f: Seq[Field] => f foreach println
}
}
}
Now each field of personX gets printed to the console. Works like a charm.
The thing is, I want to get the PersonField as well (with the Field)!
So I tried the following changes (among others that didn't work, which I can't remember)
In Person:
def fields =
{
for
{
person <- Persons.all.filter(_.id === this.id)
field <- person.fields join Fields.all on (_.fieldID === _.id)
} yield field
}
In PersonS
def fields = PersonFields.all.filter(_.personID === id) // No flatMap here!
then getFields(p: Person) looks like this:
def getFields(p: Person): Future[Seq[(PersonField, Field)]]
but
personX.onSuccess
{
case p: Person =>
{
val fields = helper.getFields(p)
fields.onSuccess
{
case f: Seq[(PersonField, Field)] => f map(f => println(f._1)}
}
}
}
gives me nothing, so I guess my join must be wrong. But what exactly am I doing wrong?

Answer 1

You can join all three, then yield the result
for {
((personField, person), field) <- PersonFields.all join Persons.all on (_.personId === _.id) join Fields.all on (_._1.fieldId === _.id)
if person.id === this.id
} yield (personField, person, field)
(I am not sure I got exactly what you were trying to get out of the query, so you can just edit the yield part )