How deal with child entites with unique attributes in JPA+Hibernate+Spring? - spring

Question

Saving a many-to-one association only works the first time.
How save father with appended child if child entries already exist and prevent the "Unique index or primary key violated" error message ?
Note: that the name attribute is unique!
The main program.
// This works
Car car1 = new Car();
Car car2 = new Car();
Car car3 = new Car();
Model model1 = new Model();
Model model2 = new Model();
model1.setName("911");
model2.setName("Vito");
car1.setLicense("S-TU-123");
car2.setLicense("S-GH-124");
car3.setLicense("S-BN-123");
car1.setModel(model1);
car2.setModel(model2);
car3.setModel(model1);
carRepository.saveAll(Arrays.asList(car1, car2, car3));
//// wont work because of "Unique index or primary key violated"
Car car4 = new Car();
Model model4 = new Model();
car4.setModel(model4);
model4.setName("911"); // <== exists in database already
car4.setLicense("L-QQ-001");
carService.save(car4);
model code:
import javax.persistence.*;
import lombok.*;
#Entity
#Table(name = "cars")
#Getter
#Setter
#EqualsAndHashCode
#NoArgsConstructor
public class Car {
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column
private String license;
#EqualsAndHashCode.Exclude
#ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
#JoinColumn(name = "model_id", referencedColumnName = "id")
private Model model;
public void setModel(Model model) {
this.model = model;
model.getCars().add(this);
}
public void removeModel(Model model) {
this.model = model;
model.getCars().add(null);
}
}
car code:
import javax.persistence.*;
import lombok.*;
import java.util.HashSet;
import java.util.Set;
#Entity
#Table(name = "models")
#Getter
#Setter
#EqualsAndHashCode
#NoArgsConstructor
public class Model {
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(unique = true)
private String name;
#EqualsAndHashCode.Exclude
#OneToMany(mappedBy = "model", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<Car> cars = new HashSet<>();
public void setCars(Set<Car> cars) {
this.cars = cars;
for (Car car : cars) {
car.setModel(this);
}
}
}
car repository:
public interface CarRepository extends JpaRepository<Car, Long> {
}
model repository:
public interface ModelRepository extends JpaRepository<Model, Long> {
Optional<Model> findByLicense(String license);
}