#AssociationOverride and #AttributeOverride in new Doctrine 2.3 - doctrine

Question

As per title, what's the purpose of the new annotation #AssociationOverride and #AttributeOverride?
The only thing I can find on Doctrine website is:
#AssociationOverride and #AttributeOverride (useful for Trait and
MappedSuperclass)

Answer 1

By looking at the code in the commit, we can see that it is used to override a field mapping already defined in a mapped superclass / trait.
The tests included in the commit demonstrate this behaviour:
Mapped superclass
/**
* #MappedSuperclass
*/
class User
{
/**
* #Id
* #GeneratedValue
* #Column(type="integer", name="user_id", length=150)
*/
protected $id;
/**
* #Column(name="user_name", nullable=true, unique=false, length=250)
*/
protected $name;
/**
* #var ArrayCollection
*
* #ManyToMany(targetEntity="Group", inversedBy="users", cascade={"persist", "merge", "detach"})
* #JoinTable(name="users_groups",
* joinColumns={#JoinColumn(name="user_id", referencedColumnName="id")},
* inverseJoinColumns={#JoinColumn(name="group_id", referencedColumnName="id")}
* )
*/
protected $groups;
/**
* #var Address
*
* #ManyToOne(targetEntity="Address", cascade={"persist", "merge"})
* #JoinColumn(name="address_id", referencedColumnName="id")
*/
protected $address;
...
}
Subclass using #AssociationOverride
/*
* #Entity
* #AssociationOverrides({
* #AssociationOverride(name="groups",
* joinTable=#JoinTable(
* name="users_admingroups",
* joinColumns=#JoinColumn(name="adminuser_id"),
* inverseJoinColumns=#JoinColumn(name="admingroup_id")
* )
* ),
* #AssociationOverride(name="address",
* joinColumns=#JoinColumn(
* name="adminaddress_id", referencedColumnName="id"
* )
* )
* })
*/
class Admin extends User
{
...
}
Subclass using #AttributeOverride
/**
* #Entity
* #AttributeOverrides({
* #AttributeOverride(name="id",
* column=#Column(
* name = "guest_id",
* type = "integer",
* length = 140
* )
* ),
* #AttributeOverride(name="name",
* column=#Column(
* name = "guest_name",
* nullable = false,
* unique = true,
* length = 240
* )
* )
* })
*/
class Guest extends User
{
...
}