How to delete parent without deleting children in one to many relationship

I am trying to delete a Patient entity without deleting the associated OutboundMessage entities as i want to keep them in the database for reporting/historical purposes. This is the relevant code :

Patient entity

@OneToMany (mappedBy="patient", fetch = FetchType.EAGER,orphanRemoval = false)
public Set<OutboundMessage> getOutboundMessages() 
{
    return outboundMessages;
}

OutboundMessage entity

@ManyToOne (fetch=FetchType.EAGER)
@JoinColumn(name = "id_patient")
public Patient getPatient() 
{
    return patient;
}

When i set a cascade type on the Patient side the records are deleted which is not what i want. When trying as shown in the code above (without the cascade type) I get the following exception :

The DELETE statement conflicted with the REFERENCE constraint "FKqjpga9w6wp3qk26ox9pg252d9". The conflict occurred in database "MDHIS", table "dbo.tblOutboundMessage", column 'id_patient'.

What settings does the owning entity need to allow deletion without cascading to children entities and without cleaning orphaned records?

Thanks!

Solution

You need to allow null values in your foreign key column (@JoinColumn) as follows:

@ManyToOne (fetch=FetchType.EAGER)
@JoinColumn(name = "id_patient", nullable = true)
public Patient getPatient() {
    return patient;
}

Then in your DAO you need to set null values for all the OutboundMessage related to the Patient you're about to delete and only then delete it, as follows:

public void deletePatient(int patientId) {
    Session currentSession = sessionFactory.getCurrentSession();

    // get patient with primary key
    Patient patient = currentSession.get(Patient.class, patientId);  
    Set<OutboundMessage> messages = patient.getOutboundMessages();

    //set patient id null
    for(OutboundMessage message : messages) {
        message.setPatient(null);
    }

    //delete the patient
    currentSession.remove(patient);
}