Hibernate: bi-directional mapping OneToMany does not work

Question

I have three classes as following:

import java.sql.Timestamp;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import javax.persistence.Transient;

import org.hibernate.annotations.Type;


@Entity

public class EventTO {

...
private List<EventAssignedResourceTO> eventAssignedResourceTOList;


/**
 * @return the eventAssignedResourceTOList
 */
@OneToMany(fetch = FetchType.LAZY,cascade=CascadeType.ALL)
@JoinColumn(name = "EAR_EVN_ID")
public List<EventAssignedResourceTO> getEventAssignedResourceTOList() {
    return eventAssignedResourceTOList;
}

/**
 * @param eventAssignedResourceTOList
 *            the eventAssignedResourceTOList to set
 */
public void setEventAssignedResourceTOList(List<EventAssignedResourceTO>   eventAssignedResourceTOList) {
    this.eventAssignedResourceTOList = eventAssignedResourceTOList;
}

public void setPrivate(boolean aPrivate) {
    setPrivateEvent(aPrivate);
}

}

The second class:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import javax.persistence.Transient;


@Entity
public class EventAssignedResourceTO  {

private EventTO eventTO;
private EventResourceTO eventResourceTO;
private int resourceCount;


/**
 * @return the eventTO
 */
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "EAR_EVN_ID", updatable = false, insertable=false, nullable = false)
public EventTO getEventTO() {
    return eventTO;
}

/**
 * @param eventTO
 *            the eventTO to set
 */
public void setEventTO(EventTO eventTO) {
    this.eventTO = eventTO;
}


/**
 * @return the eventResourceId
 */
@Transient
public Long getEventResourceId() {
    return eventResourceId;
}

/**
 * @param eventResourceId
 *            the eventResourceId to set
 */
public void setEventResourceId(Long eventResourceId) {
    this.eventResourceId = eventResourceId;
}

/**
 * @return the resourceCount
 */
@Column(name = "EAR_COUNT")
public int getResourceCount() {
    return resourceCount;
}

/**
 * @param resourceCount
 *            the resourceCount to set
 */
public void setResourceCount(int resourceCount) {
    this.resourceCount = resourceCount;
}

/**
 * @return the eventResourceTO
 */
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "EAR_ERS_ID")
public EventResourceTO getEventResourceTO() {
    return eventResourceTO;
}

/**
 * @param eventResourceTO
 *            the eventResourceTO to set
 */
public void setEventResourceTO(EventResourceTO eventResourceTO) {
    this.eventResourceTO = eventResourceTO;
}
}

The third class:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

import org.hibernate.annotations.Type;


@Entity
public class EventResourceTO {
private String name;
private int count;
private boolean active;

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq")
@Column(name = "ERS_ID")
public Long getId() {
    return super.getId();
}

/**
 * @return the name
 */
@Column(name="ERS_NAME")
public String getName() {
    return name;
}

/**
 * @param name
 *            the name to set
 */
public void setName(String name) {
    this.name = name;
}

/**
 * @return the count
 */
@Column(name="ERS_COUNT")
public int getCount() {
    return count;
}

/**
 * @param count
 *            the count to set
 */
public void setCount(int count) {
    this.count = count;
}

/**
 * @return the active
 */
@Type(type="yes_no")
@Column(name="ERS_IS_ACTIVE")
public boolean isActive() {
    return active;
}

/**
 * @param active
 *            the active to set
 */
public void setActive(boolean active) {
    this.active = active;
}

}

I have followed the official hibernate documentation here: http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html_single/#collections-bidirectional

and this example here: http://viralpatel.net/blogs/hibernate-one-to-many-annotation-tutorial/

The problem is that while inserting the EventTO in DB I get a constraint violation on the eventId because hibernate cannot set the id of newly created event in the eventTO in EventAssignedResourceTO and the id is null .

So I decided to remove the updatable and insertable tag in the JoinColumn annotation in the EventAssignedResourceTO.

Now the insert works properly but when I want to delete an Event, hibernate deletes the AssignedResourceTO first then the event and at the end I don't know why it tries to update the record of AssignedResourceTO in its table. Here it tries to set the id of eventTO to NULL and I get constraint violation. the same also occurs for update.

I'm really confused since what is written in the official documentation does not work and I was unable to find any solution on the web.

any idea??

Cheers

Answer 1

You don't need @JoinColumn(name = "EAR_EVN_ID") in EventTO class. Instead add mappedBy to the association. So:

@OneToMany(mappedBy = "eventTO", fetch = FetchType.LAZY,cascade=CascadeType.ALL)
public List<EventAssignedResourceTO> getEventAssignedResourceTOList() {
    return eventAssignedResourceTOList;
}

Also fetch is by default LAZY for @OneToMany associations, you can remove that too.

Answer 2

for bidirectional mapping use JoinColumn annotation only at Parent and use mappedBy property in child .and for removing recurrence between parent and child entity use these annotations.

@OneToMany(
            mappedBy = "queue_group",fetch = FetchType.LAZY,
            cascade = CascadeType.ALL
        )
    @JsonManagedReference
    private Set<Queue> queues;

 @ManyToOne(cascade=CascadeType.ALL)
        @JoinColumn(name = "qid")
       // @JsonIgnore
        @JsonBackReference
        private Queue_group queue_group;