休眠联接中的多对一联接

Question

I want to make join between Entry entity and Project entity. My goal is to search entries by assigned project id. I enter project id and i want to get all entries with this project assigned.

This is my method in DAO class

@Override
    public PageWrapper<Entry> getListOfEntries(EntrySC sc) {
        public PageWrapper<Entry> getListOfEntries(EntrySC sc) {
    CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
    CriteriaQuery<Entry> cq = cb.createQuery(Entry.class);
    Root<Entry> entry = cq.from(Entry.class);
    //Join<Entry,Project> join = cq.from(Entry.class).join(Entry_.project);

    cq.select(entry);

    PageWrapper<Entry> results = new PageWrapper<>();
    results.setResults(em.createQuery(cq).getResultList());
    results.setRows(em.createQuery(cq).getResultList().size());

    return results;
    }

And this is my Entry entity and Project entity

@Entity
@Table(name = "Entry")
@NamedQueries({
    @NamedQuery(name="Entry.findAll", query="SELECT e FROM Entry e ORDER BY e.date DESC"),
    @NamedQuery(name="Entry.findByID", query="SELECT e FROM Entry e WHERE e.id = :entryID"),
    @NamedQuery(name="Entry.findByUserID", query="SELECT e FROM Entry e WHERE e.user.id = :userID ORDER BY e.date DESC"),
    @NamedQuery(name="Entry.findByProjectID", query="SELECT e FROM Entry e WHERE e.project.id = :projectID")
})
public class Entry extends BaseEntityAudit {


    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "PROJECT_ID", nullable = false)
    @JsonIgnore
    private Project project;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "USER_ID", nullable = false)
    @JsonIgnore
    private User user;

    @Column(name = "COMMENT", nullable = true)
    private String comment;

    @Column(name = "HOURS", nullable = false)
    private BigDecimal hours;

    @Column(name = "DATE", nullable = false)
    @Temporal(javax.persistence.TemporalType.DATE)
    private Date date;


    public Entry(){}

    //setters and getters

}

@Entity
@Table(name="Project")
@NamedQueries({
    @NamedQuery(name="Project.findAll", query="SELECT p FROM Project p"),
    @NamedQuery(name="Project.findByID", query="SELECT p FROM Project p WHERE p.id = :projectID")
})
public class Project extends BaseEntityAudit {

    @Column(name="NAME", nullable=false)
    private String name;

    @Column(name="START_DATE", nullable=false)
    @Temporal(TemporalType.DATE)
    private Date startDate;

    @Column(name="DUE_DATE")
    @Temporal(TemporalType.DATE)
    private Date dueDate;

    @Column(name="COMMENT", nullable=true)
    private String comment;


    public Project(){

    }

    //setters and getters
}

The project class dont know about entries. Maybe this is the problem?

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Edit:

I created join base on documentation. But its not clear to me. Because if i uncomment this i will get null pointer exception. I also created metamodel class

@StaticMetamodel(Entry.class)
public class Entry_ {

    public static volatile SingularAttribute<Entry,Project> project;

    public static volatile SingularAttribute<Entry,User> user;

    public static volatile SingularAttribute<Entry, String> comment;

    public static volatile SingularAttribute<Entry,BigDecimal> hours;

    public static volatile SingularAttribute<Entry,Date> date;

}

Answer 1

Provided that you already defined the NamedQuery annotations, I suppose you intended to use them when querying. Here you can find the examples you need. Otherwise if you prefer to construct the query with CriteriaQuery you can adopt these examples.