In the previous chapter, we showed you how to apply filters using annotation. Another way is to apply filters to a collection that is already in the persistence context. This is quite useful to fetch only a subset of a collection.
For example, if you have a list of teachers and their students in the database and you are simply interested in fetching the records for all the female students, you can use filters, which can be very efficient in some cases.
To demonstrate how to use filters, let's assume that we have the following entities:
@Entity
public class Teacher {
@Id
@GeneratedValue
private long id;
private String name;
@OneToMany(cascade=CascadeType.ALL)
Set<Student> students = new HashSet<Student>();
// getters and setters
}
@Entity
public class Student {
@Id
@GeneratedValue
private long id;
private String name;
private String gender;
// getters and setters
}You can get the teacher record using a simple fetch:
Teacher teach = (Teacher) session...