I've 2 tables Employee & Vehicle, where one employee can have multiple vehicles.
Below is the mapping that I've defined:
Employee.java
#Entity(name = "emp_details")
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int empId;
#OneToMany(cascade = CascadeType.ALL, mappedBy="employee")
private List<Vehicle> vehicles = new ArrayList<>();
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public List<Vehicle> getVehicles() {
return vehicles;
}
public void setVehicles(List<Vehicle> vehicles) {
this.vehicles = vehicles;
}
}
Vehicle.java
#Entity
public class Vehicle {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int vehicleId;
#ManyToOne
#JoinColumn(name="empId")
private Employee employee;
private String name;
public Employee getEmployee() {
return employee;
}
public void setEmployee(Employee employee) {
this.employee = employee;
}
public int getVehicleId() {
return vehicleId;
}
public void setVehicleId(int vehicleId) {
this.vehicleId = vehicleId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Main class
public class HibernateTest {
public static void main(String[] args) {
Employee emp = new Employee();
Vehicle vehicle = new Vehicle();
vehicle.setName("Honda");
emp.getVehicles().add(vehicle);
SessionFactory sFactory = new Configuration().configure().buildSessionFactory();
Session session = sFactory.openSession();
session.beginTransaction();
session.save(emp);
session.getTransaction().commit();
session.close();
StandardServiceRegistryBuilder.destroy(sFactory.getSessionFactoryOptions().getServiceRegistry());
}
}
But when I execute this, Vehicle.employee_id is empty. I was expecting that my foreign key will be inserted there.
What am I missing?
Thank You
You need to show us the code that persists your entities, but my guess is that you are not setting the employee to the vehicle.
You need to manage both sides of bidirectional entity relationship. Your code should look something like this
employee.getVehicles().add(vehicle);
vehicle.setEmployee(employee);
session.save(employee);
UPDATE:
In this case, Vehicle is the owning side of the relation because the foreign key is in its database table. You just added the new vehicle to the employee's list of vehicles. When you save the employee, there's nothing to change in Employees database, and the save operation cascades to Vehicle. Vehicle does not have its employee set, it is null, so it puts null in empId column
Bottom line, you have to make sure both sides of bidirectional relationship are wired up correctly.
If you have a bidirectional relationship you have to
set the relation on both sides.
That means you have to set the employee for your vehicle also.
You can do this by calling
vehicle.setEmployee(emp);
and then store or update your entity (if it's not attached to session already).
Usually to set a bidirectional relationship you provide special methods in your entities.
public class Vehicle {
...
public void setEmployee(Employee employee) {
this.employee = employee;
employee.addVehicle(this)
}
...
}
public class Employee {
...
public void addVehicle(Vehicle v) {
if(!vehicles.contains(v)) {
vehicles.add(v);
}
if(!this.equals(v.getEmployee()) {
v.setEmployee(this);
}
}
...
}
In your Employee entity class, you haven't used #Column annotation on empId. In Vehicle class you are referencing Employee using #JoinColumn(name="employee_id"),so column employee_id must exist in emp_details table. So you need to modify your Employee class to something with
#Id
#GeneratedValue
#Column(name="employee_id")
private int empId;
I think need to edit your code. you miss the entity jpa rule. you can some search jpa entity. you read description for you. link : enter link description here
(Modified your Employee.java)
#Entity(name = "employee")
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int idx;
#OneToMany(cascade = {CascadeType.ALL}, mappedBy = "employee")
private List<Vehicle> vehicle = new ArrayList<>();
...
}
(Modified your Vehicle.java)
#Entity
public class Vehicle {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int idx;
#ManyToOne
#JoinColumn(name="employee_id")
private Employee employee;
...
}
You only need to cascade onetoMany from Employee Entity
Related
I'm trying to see whether a Cab is assigned to any Employee so I can fetch that Employee Id and simply to set cab as null, but #OneToMany mapping, simply returning a list of Employees & by this I'm not getting any method like a cab.getEmp() to fetch employee details
Employee.java
#Data
#Entity
#Table(name = "employee")
public class Employee {
#Id
private Integer id;
private String username;
private String password;
private String role;
private String dropLocation;
#ManyToOne(
cascade = CascadeType.ALL,
fetch = FetchType.EAGER
)
#JoinColumn(
name = "empCab",
referencedColumnName = "cabId"
)
public Cab cab;
}
Cab.java
#Data
#Entity
#Table(name = "cab")
public class Cab {
#Id
private Integer cabId;
private Integer cabNumber;
private String cabShift;
#OneToMany(
cascade = CascadeType.ALL,
fetch = FetchType.EAGER,
mappedBy= "cab"
)
private List<Employee> emp = new ArrayList<>();
}
Controller
#GetMapping("deleteCab")
public ModelAndView deleteCab(#RequestParam("id") Integer id, ModelAndView mvc){
Cab cab = cabRepo.findById(id).orElse(null);
if(cab!=null){
List<Employee> emp = cab.getEmp();
if(!cab.getEmp().isEmpty()){
//e1.setCab(null);
//empRepo.save(e1);
mvc.addObject("msg", "Cab deleted & an employee cab detail also got changed");
mvc.setViewName(NOTHING_JSP);
} else {
cabRepo.deleteById(id);
mvc.addObject("msg", "Cab removed from the database");
mvc.setViewName(NOTHING_JSP);
}
}
}
In your code, Cab is perent class and Employee is child class and your goal is to remove the child class dependency with parent class. For that, You have to extract the Employee from Cab and remove the relationship with Cab using employee.setCab(null).
#GetMapping("/deleteCab")
#ResponseBody
public ModelAndView deleteCab(#RequestParam("id") Integer id, ModelAndView mvc){
Cab cab = cabRepo.findById(id).orElse(null);
if(cab != null){
// Extract employee from cab
for(Employee emp: cab.getEmp())
{
// Remove the relationship with cab
emp.setCab(null);
}
cabRepo.save(cab);
mvc.addObject("msg", "Cab deleted & an employee cab detail also got changed");
mvc.setViewName(NOTHING_JSP);
} else {
cabRepo.deleteById(id);
mvc.addObject("msg", "Cab removed from the database");
mvc.setViewName(NOTHING_JSP);
}
return mvc;
}
I have two classes, CarRentalCompany
#Entity
public class CarRentalCompany {
private static Logger logger = Logger.getLogger(CarRentalCompany.class.getName());
#Id
private String name;
#OneToMany(cascade = CascadeType.ALL)
private List<Car> cars;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<CarType> carTypes = new ArrayList<>(); //TODO: kan betere datastructuur zijn
/***************
* CONSTRUCTOR *
***************/
public CarRentalCompany()
{
// DEFAULT CONSTRUCTOR
}
public CarRentalCompany(String name, List<Car> cars) {
logger.log(Level.INFO, "<{0}> Car Rental Company {0} starting up...", name);
setName(name);
this.cars = cars;
for(Car car:cars)
carTypes.add(car.getType());
}
...
}
and CarType
#Entity
public class CarType {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
private String name;
private int nbOfSeats;
private boolean smokingAllowed;
private double rentalPricePerDay;
//trunk space in liters
private float trunkSpace;
/***************
* CONSTRUCTOR *
***************/
public CarType()
{
}
public CarType(String name, int nbOfSeats, float trunkSpace, double rentalPricePerDay, boolean smokingAllowed) {
this.name = name;
this.nbOfSeats = nbOfSeats;
this.trunkSpace = trunkSpace;
this.rentalPricePerDay = rentalPricePerDay;
this.smokingAllowed = smokingAllowed;
}
When running the application, it throws the following exception:
NucleusFatalUserException: Attempt to assign child with key
"CarType(6614661952700416)" to parent with key
"CarRentalCompany("Hertz")". Parent keys are immutable
What do I need to do to get the key of the CarType right?
You are not persisting your CarRentalCompany entity before adding CarType entity. See a
similar thread here. The persist operation must be used only for new entities. An entity is new when it has never been associated with a database row, meaning that there is no table record in the database to match the entity in question.
I am unsuccessfuly trying to create bridge table that would resolve two #ManyToMany relations. However this table have to contain additional field. For example:
Course: -course_id - pk
Student: -student_id -pk
Bridge: -(course_id, student_id) - pk
-additional_field
My student class looks like this:
#Entity
public class Student extends Model {
#Id
#OneToMany
public List<Bridge> student_id;
}
Course class is basicaly the same.
Bridge table looks like this:
#Entity
public class Bridge extends Model{
#EmbeddedId
public compound_key student_course;
public String additional_field;
#Embeddable
public class compound_key{
#ManyToOne
public Student student_id;
#ManyToOne
public Student course_id;
}
}
Thank you for help.
I have found the following solution. This is a solution without a composite key in Bridge. I added normal #Id field in Bridge class and relations to Student and Course are normal relations.
This solution contains an additional 'id' field in the 'bridge' table in the database.
Here is the code:
Student.java:
#Entity
public class Student extends Model {
#Id
public Integer id;
#OneToMany(mappedBy="student")
public List<Bridge> bridges;
public static Finder<Integer,Student> find = new Finder<Integer,Student>(
Integer.class, Student.class
);
}
Course.java:
#Entity
public class Course extends Model {
#Id
public Integer id;
#OneToMany(mappedBy="course")
public List<Bridge> bridges;
public static Finder<Integer,Course> find = new Finder<Integer,Course>(
Integer.class, Course.class
);
}
Bridge.java:
#Entity
public class Bridge extends Model {
#Id
public Integer id;
#ManyToOne public Student student;
#ManyToOne public Course course;
public String additional_field;
public static Finder<Integer,Bridge> find = new Finder<Integer,Bridge>(
Integer.class, Bridge.class
);
}
EDIT
After many attempts I have found solution with composite key in Bridge class. Classes Student and Course are the same as in previous solution.
Bridge.java changed to following:
#Entity
public class Bridge extends Model {
Bridge() {
bridgeId = new BridgeId();
}
#EmbeddedId
protected BridgeId bridgeId;
#ManyToOne
#JoinColumn(name = "student_id", insertable = false, updatable = false)
private Student student;
#ManyToOne
#JoinColumn(name="course_id", insertable = false, updatable = false)
private Course course;
public String additional_field;
public Student getStudent() {
return student;
}
public void setStudent(Student aStudent) {
student=aStudent;
bridgeId.student_id = aStudent.id;
}
public Course getCourse() {
return course;
}
public void setCourse(Course aCourse){
course=aCourse;
bridgeId.course_id = aCourse.id;
}
}
And there is additional BridgeId.java:
#Embeddable
public class BridgeId implements Serializable
{
public Integer student_id;
public Integer course_id;
public int hashCode() {
return student_id + course_id;
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
BridgeId b = (BridgeId)obj;
if(b==null)
return false;
if (b.student_id == student_id && b.course_id == course_id) {
return true;
}
return false;
}
}
What is more important in this code is:
Fields of embedded id are mapped to the same columns as ManyToOne relations.
Value to 'student_id' and 'course_id' columns are inserted from embedded id and not from relations. This is because relations have attributes 'insertable' and 'updatable' set to false.
I had to add getters and setters to 'student' and 'course' fields. In setters I am updating fields of embedded key.
Above solution has several workarounds. But I wasn't ableto find easier and cleaner one.
I am trying to set up a ManyToMany Relationship in JPA with additional columns in the join table.
I followed the example and testcode from here:
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany
If I run the code I get the following exception:
Caused by: org.hibernate.AnnotationException: package.ProjectAssociationId has no persistent id property
at org.hibernate.cfg.AnnotationBinder.bindIdClass(AnnotationBinder.java:2507)
at org.hibernate.cfg.AnnotationBinder.mapAsIdClass(AnnotationBinder.java:845)
at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:671)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processAnnotatedClassesQueue(Configuration.java:3466)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processMetadata(Configuration.java:3420)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1348)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1747)
at org.hibernate.ejb.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:96)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:913)
... 51 more
I tried to add different annotations to the ProjectAssociationId, but did not get it to work. Do I need any kind of ID in ProjectAssociationId? I don't think so because this is not actually persisted. But about what is hibernate complaining then about exaclty?
This is the code:
#Entity
public class Employee {
#Id
private long id;
...
#OneToMany(mappedBy="employee")
private List<ProjectAssociation> projects;
...
}
#Entity
public class Project {
#Id
private long id;
...
#OneToMany(mappedBy="project")
private List<ProjectAssociation> employees;
...
// Add an employee to the project.
// Create an association object for the relationship and set its data.
public void addEmployee(Employee employee, boolean teamLead) {
ProjectAssociation association = new ProjectAssociation();
association.setEmployee(employee);
association.setProject(this);
association.setEmployeeId(employee.getId());
association.setProjectId(this.getId());
association.setIsTeamLead(teamLead);
this.employees.add(association);
// Also add the association object to the employee.
employee.getProjects().add(association);
}
}
#Entity
#Table(name="PROJ_EMP")
#IdClass(ProjectAssociationId.class)
public class ProjectAssociation {
#Id
private long employeeId;
#Id
private long projectId;
#Column(name="IS_PROJECT_LEAD")
private boolean isProjectLead;
#ManyToOne
#PrimaryKeyJoinColumn(name="EMPLOYEEID", referencedColumnName="ID")
private Employee employee;
#ManyToOne
#PrimaryKeyJoinColumn(name="PROJECTID", referencedColumnName="ID")
private Project project;
...
}
public class ProjectAssociationId implements Serializable {
private long employeeId;
private long projectId;
...
public int hashCode() {
return (int)(employeeId + projectId);
}
public boolean equals(Object object) {
if (object instanceof ProjectAssociationId) {
ProjectAssociationId otherId = (ProjectAssociationId) object;
return (otherId.employeeId == this.employeeId) && (otherId.projectId == this.projectId);
}
return false;
}
}
I created two entities for the tables HOBBY and STUDENT, but I have difficulties to retrieve the information I need from the Join Table.
This is the schema:
STUDENT STUDENT_HOBBY HOBBY
-------- ----------- --------
id ------------------ student_id
name hobby_id ---------- id
lastname hobby_name
--------- ---------- --------
where
Student to student_hobby = one to many
Hobby to student_hobby = one to many
(that means a student may have many hobbies and a hobby can belong to more than one student)
This is the Student entity class:
#Entity
#Table(name="STUDENT")
public class Student {
#OneToMany
#JoinTable(name="student_hobbies", joinColumns=#JoinColumn(name="student_id"),
inverseJoinColumns=#JoinColumn(name="hobby_id"))
private Collection<Hobby> hobbies;
#Id
#Column(name="ID")
#GeneratedValue
private Integer id;
#Column(name="NAME")
private String name;
#Column(name="LASTNAME")
private String lastName;
// Getters and setters here
}
This is the Hobby entity class:
#Entity
#Table(name="HOBBY")
public class Hobby {
#OneToMany
#JoinTable(name="student_hobbies", joinColumns=#JoinColumn(name="hobby_id"),
inverseJoinColumns=#JoinColumn(name="student_id"))
private Collection<Student> students;
#Id
#Column(name="ID")
#GeneratedValue
private Integer id;
#Column(name="HOBBY_NAME")
private String hobby_name;
// Getters and setters here
}
Now I would like to implement the following DAO, but I don't know exactly how to do:
public interface MyDAO {
public void addHobbyForStudent(int student_id, int hobby_id);
public void RemoveHobbyForStudent(int student_id, int hobby_id);
}
Should I create an other entity class for the Join Table? Could someone give me some indication on the way to follow?
You can create an entity class for the join table, but you don't need to and you probably shouldn't. This will just create more code to maintain. You should create an entity for the join table if there is data in the join table you need to query. EG: if there was a start_time or something in the join table and you wanted to be able to see the start_time.
You should be using the #ManyToMany annotation when you're avoiding a join table entity. The documentation I linked to gives some good examples of how to do this:
Example 1:
// In Customer class:
#ManyToMany
#JoinTable(name="CUST_PHONES")
public Set<PhoneNumber> getPhones() { return phones; }
// In PhoneNumber class:
#ManyToMany(mappedBy="phones")
public Set<Customer> getCustomers() { return customers; }
Example 2:
// In Customer class:
#ManyToMany(targetEntity=com.example.PhoneNumber.class)
public Set getPhones() { return phones; }
// In PhoneNumber class:
#ManyToMany(targetEntity=com.example.Customer.class, mappedBy="phones")
public Set getCustomers() { return customers; }
Example 3:
// In Customer class:
#ManyToMany
#JoinTable(name="CUST_PHONE",
joinColumns=
#JoinColumn(name="CUST_ID", referencedColumnName="ID"),
inverseJoinColumns=
#JoinColumn(name="PHONE_ID", referencedColumnName="ID")
)
public Set<PhoneNumber> getPhones() { return phones; }
// In PhoneNumberClass:
#ManyToMany(mappedBy="phones")
public Set<Customer> getCustomers() { return customers; }