Hibernate - insert data with one to many relationship

I am trying to insert data into a Patient table, which has a many-to-one relationship with Site. Site has a one-to-many relationship with Patient.

However, I get a org.postgresql.util.PSQLException: ERROR: insert or update on table "patients" violates foreign key constraint "fk_427e3ubwhw8n7a4id3mmrmjgj" Detail: Key (patient_id)=(31) is not present in table "sites".

I have tried to create a set of patients, add my patient to this set, create a site object, then use this object to set the patients. I am not sure which part of this is going wrong.

 Session session = this.getFactory().openSession(); Transaction transaction = null; try{ transaction = session.beginTransaction(); Date parsedDob = Date.valueOf(dob); Date parsedDateReg = Date.valueOf(dateReg); Site site = new Site(); site.setSiteId(1); IPatient p = new Patient(); p.setFirstName(firstName); p.setLastName(lastName); p.setDob(parsedDob); p.setDateRegistered(parsedDateReg); p.setSite(site); Set<IPatient> patientSet = new HashSet<IPatient>(); patientSet.add(p); site.setPatients(patientSet); session.save(site); session.save(p); transaction.commit(); }catch(Exception e){ e.printStackTrace(); } 

My Patient.hbm.xml file is:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.example.model"> <class name="Patient" table="patients"> <id name="patientId" column="patient_id"> <generator class="sequence" /> </id> <version name="version" column="version" /> <property name="firstName" column="first_name" /> <property name="lastName" column="last_name" /> <property name="dob" column="dob" /> <property name="gender" column="gender" /> <property name="dateRegistered" column="date_registered" /> <many-to-one name="site" class="com.example.model.Site" not-null="true" /> <set name="visits" cascade="all"> <key column="visit_id" /> <one-to-many class="Visit" /> </set> </class> 

My Site.hmx.xml is:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.example.model"> <class name="Site" table="sites"> <id name="siteId" column="site_id"> <generator class="sequence" /> </id> <version name="version" column="version" /> <property name="name" column="name" /> <set name="patients" cascade="all"> <key column="patient_id" /> <one-to-many class="Patient" /> </set> </class> 

My Patient.java

public class Patient implements IPatient{ private Integer version; private Integer patientId; private Set<IVisit> visits; private Site site; private String firstName; private String lastName; private Date dob; private Gender gender; private Date dateRegistered; public Patient(){ } } 

My Site.java

public class Site { private Integer siteId; private Integer version; private Set<IPatient> patients; private String name; public Site(){ } }