@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class Party {
    ....
    ....

}

@Entity
public class Person extends Party {

    /**
     */
    @NotNull
    private String firstName;

    /**
     */
    @NotNull
    private String lastName;
    ....
    ....
  
}

@Entity
public class Organization extends Party {

    /**
     */
    @NotEmpty
    @NotNull
    private String name;
    ....
    ....

}

@Entity
public class WorkOrder {
    ....
    ....
    /**
     */
    @NotNull
    @ManyToOne(fetch = FetchType.LAZY)
    private Party assignedTo;
}

select distinct entity
from WorkOrder entity
  ....
  ....
  left join treat(entity.assignedTo as Person) as assignedToPerson
  left join treat(entity.assignedTo as Organization) as assignedToOrganization
where ..... 
lower(assignedToPerson.firstName) like :1  or lower(assignedToPerson.lastName) like :1  or lower(assignedToOrganization.name) like :1

select
distinct workorder0_.id as col_0_0_,
workorder0_.assigned_to as col_1_0_,
party6_.id as id1_66_,
....
....
party6_2_.name as name4_64_,
case when party6_1_.id is not null then 1 when party6_2_.id is not null then 2 when party6_.id is not null then 0 end as clazz_
from public.work_order workorder0_ left outer
.....
.... 
left outer join public.party party6_ on workorder0_.assigned_to=party6_.id
inner join public.person party6_1_ on party6_.id=party6_1_.id
inner join public.organization party6_2_ on party6_.id=party6_2_.id
where .... 
or lower(party6_1_.first_name)  like ?1
or lower(party6_1_.last_name) like ?1
or lower(party6_2_.name) like ?1

select
distinct workorder0_.id as col_0_0_,
workorder0_.assigned_to as col_1_0_,
party6_.id as id1_66_,
....
....
party6_2_.name as name4_64_,
case when party6_1_.id is not null then 1 when party6_2_.id is not null then 2 when party6_.id is not null then 0 end as clazz_
from public.work_order workorder0_ left outer
.....
.... 
left outer join public.party party6_ on workorder0_.assigned_to=party6_.id
left join public.person party6_1_ on party6_.id=party6_1_.id
left join public.organization party6_2_ on party6_.id=party6_2_.id
where .... 
or lower(party6_1_.first_name)  like ?1 
or lower(party6_1_.last_name) like ?1
or lower(party6_2_.name) like ?1