JPA or Hibernate or Spring for specifying a query for a relationship?
Is it possible to explicitly specify a query to run to collect related entities using JPA or Hibernate annotations?
Specifically, I have the following objects: Tutor, Student, and an explicit OneToOne relationship between Tutor and Student, Tutorial:
@Entity
public class Student {
@OneToMany Collection<Tutorial> tutorials;
}
@Entity
public class Tutor {
@OneToMany Collection<Tutorial> tutorials;
}
@Entity
public class Tutorial {
@OneToOne Tutor tutor;
@OneToOne Student student;
// other data
}
A student can be assigned as a Homework Teacher in the Study Guide (but not a mentor who has not been assigned a student), so:
@Entity
public class Homework {
@ManyToOne Tutorial tutorial;
// other data
}
Now I want to get all the students homework:
@Entity
public class Student {
@OneToMany Collection<Tutorial> tutorials;
@OneToMany Collection<Homework> homework;
}
But there is no Student in Homework; he has a tutorial. It's easy to express in SQL:
select a.*
from Homework a
join Tutorial b on (a.tutorial_id = b.id)
where b.student_id = ?student.id?
Can I express this using JPA or Hibernate or Spring annotations directly in the student class so that it is used when I call Student.getHomework ()?
In other words, I want:
@Entity
public class Student {
@OneToMany Collection<Tutorial> tutorials;
@ExplicitQuery("select Homework where Homework.student = this or something")
@OneToMany Collection<Homework> homework;
}
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You should be able to do this in Hibernate using a custom loader
@Entity
@NamedNativeQuery(name="customHomeworkLoader", query="select a.* from Homework a join Tutorial b on (a.tutorial_id = b.id) where b.student_id = ?", resultClass = Homework.class)
public class Student {
@OneToMany Collection<Tutorial> tutorials;
@Loader(namedQuery = "customHomeworkLoader")
@OneToMany Collection<Homework> homework;
}
The positional parameter ( ?
) in a named query should be automatically replaced with the primary key at runtime. I have not tried this code, so I cannot guarantee that it will work, but hopefully it will give you a hint on how to proceed.
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