How to override trait variable name in Scala

Question

I have scala trait as follows

trait Id {
            @javax.persistence.Id
            @GeneratedValue(strategy=GenerationType.IDENTITY)
            @BeanProperty
            var id: Long = _
}

Now I have an entity (Person) that I want to extend the Id trait but change the id column name to personid. How can I achieve this?
Person Snippet Below:

@NamedQuery(name=”findAll”,query=”select p from Person p”)
class Person extends Id {
    @BeanProperty
    @Column(name=”personid”)
    def personid = id
}

axel22 · Accepted Answer · 2012-06-21 12:15:06Z

5

You can introduce a method personid which returns the value of id:

trait Person extends Id {
  def personid = id
}

Removing the id member in Person would violate the principle that subclasses instances must always be usable as if they were instance of the base class. That is, if Person extends Id, then you must be able to call all the methods of id on it, otherwise you would not be able to assign an object of type Person to a reference of type Id.

So, if you extend Id, the extended trait/class will always have id.

You can, however, restrict the visibility of id in the base trait Id by making id package-private:

private[package_name] var id: Long = _

answered Jun 21, 2012 at 12:15

axel22

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2 Comments

kombo Over a year ago

Now the insert works but when I tried to load the Entity list I get an error: Unknown column ‘person0_.id’ in ‘field list’.

axel22 Over a year ago

Can you edit your post with the complete concise snippet that you are executing?

Emil L · Accepted Answer · 2012-06-23 17:46:57Z

2

If what you want to do is to simply override the column name used by JPA to then you should be able to use the AttributeOverride annotation.

It might look something like:

@MappedSuperclass
trait Id {
        @javax.persistence.Id
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        @BeanProperty
        var id: Long = _
}

@Entity
@AttributeOverride(name="id", column=@Column(name="personid"))
class Person extends Id

If you want to change the property name used to access id then you could do something like Alex is suggesting...

Edit: Forgot to let the Person entity extend the Id trait

edited Jun 23, 2012 at 17:46

answered Jun 21, 2012 at 12:58

Emil L

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