CODEWITHSUNDEEP
javahibernatelazy-initialization
Alexander Fall
Alexander Fall

Reputation: 75

Hibernate failed to lazily initialize a collection of role could not initialize proxy - no Session

I've been trying to figure out how to get this to work with a Lazy fetch type, but I can't quite figure it out.

@Entity
@Table(name = "module")
public class Module extends ReservationOption{

    @Column
    private String name;

    @Column
    private int credits;

    @Column
    private int weeks;

    @Column(name = "no_of_lectures")
    private int noOfLectures;

    @Column(name ="no_of_practicals")
    private int noOfPracticals;

    @Column(name = "lecture_length")
    private int lectureLength;

    @Column(name = "practical_length")
    private int practicalLength;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(
            name = "takes",
            joinColumns = @JoinColumn(name = "moduleID"),
            inverseJoinColumns = @JoinColumn(name = "studentID")
    )
    private Set<Student> students = new HashSet<>();

    public void addTakes(Student student){
        IDatabase db = Database.getInstance();
        if(!db.checkInTable(Student.class, student.getId())) db.add(student);
        Hibernate.initialize(students);
        students.add(student);
        student.getModules().add(this);
        db.update(this);
    }

@Entity
@Table(name = "student")
public class Student extends Person{

    /**
     * Constructor for Student class, allows for object creation
     * @param id From Person
     * @param firstName From Person
     * @param lastName From Person
     */
    public Student(String id, String firstName, String lastName) {
        super(id, firstName, lastName);
    }

    /**
     * Blank constructor to allow for database interfacing
     */
    public Student(){
        super();
    }

    @ManyToMany(mappedBy = "students", fetch = FetchType.LAZY)
    private Set<Module> modules = new HashSet<>();

    @Override
    public Set<Module> getModules() {
        return modules;
    }

    public void setModules(Set<Module> modules) {
        this.modules = modules;
    }


}

The error is being thrown on the line Hibernate.initialize(students); or on the next line if that isn't there, on the students set, with the error in the title. Any help (that's not just set fetch type to Eager) would be appreciated.

Upvotes: 1

Views: 3091

Answers (2)

Atmas
Atmas

Reputation: 2393

Check the code path to make sure a Session is explicitly or implicitly (via Annotation, for example) created.

"No session" error usually means you're trying to call Hibernate behavior (i.e. Initialize, or just access a lazy variable) but there's NO Transaction/Session resources started up for it to operate within.

Usually when this happened to me in the past it was because it was plain java code that either hadn't set up Hibernate appropriately (hence, no Session existed to bolt on to) or I had set up Hibernate, but the code found a path in such a way that it never hit a @Transactional annotation, and therefore no Session was set up.

Upvotes: 2

Simon Martinelli
Simon Martinelli

Reputation: 36133

There are various options:

  1. Call a method on the mapped relation
  2. Fetch Join in JPQL
  3. Fetch Join in Criteria API
  4. Named Entity Graph
  5. Dynamic Entity Graph

For details please read: https://thorben-janssen.com/5-ways-to-initialize-lazy-relations-and-when-to-use-them/

Upvotes: 1

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