I have two entities as following, when I try to add items to my car table it shows following error message;therefore, it does not allow me to have more than one car with 'Auto' transmission.
Error:
#1062 - Duplicate entry 'Auto' for key 'UK_bca5dfkfd4fjdhfh4ddirfhdhesr'
Entities:
Car
@Entity
public class Car implements java.io.Serializable {
@Id
@GeneratedValue
long id;
@Column(name="transmission", nullable = false)
String transmission;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
Set<CarFactory> factories;
...
}
Sample values for car table:
10 Auto
12 Auto
43 Manual
54 Manual
65 Normal
68 Standard
90 Normal
99 NoGear
CarFactory
@Entity
public class CarFactory implements java.io.Serializable {
@Id
@JoinColumn(name="transmission",referencedColumnName = "transmission")
@ManyToOne
Car car;
@Id
@JoinColumn(name="factory_id", referencedColumnName= "id")
@ManyToOne
Factory factory;
...
}
Expected values for CarFactory table
Auto Fac1
Auto Fac2
Manual Fac1
Auto Fac5
Standard Fac6
Normal Fac3
NoGear Fac1
Ive followed answer of this question as well but it did not work.
Long story short, I need to have a table with two foreign keys from other tables, with combined primary key. It should not force unique foreign key in participating tables.
A foreign key helps to define the relationship among tables . This unique key communicates one or more interrelationships in a relational database between two or more tables.
After you have finished adding tables and queries to the Relationships document tab, click Close. Drag a field (typically the primary key) from one table to the common field (the foreign key) in the other table. To drag multiple fields, press the CTRL key, click each field, and then drag them.
The problem here is that you are using a non primary key field as a foreign key which seems to be incorrect and your transmission
field, should be unique, this line is incorrect:
@JoinColumn(name="transmission",referencedColumnName = "transmission")
You have a Many-To-Many
mapping here which needs an @EmbeddedId property in the association table, and your code should be like this:
CarFactory class
@Entity
public class CarFactory {
private CarFactoryId carFactoryId = new CarFactoryId();
@EmbeddedId
public CarFactoryId getCarFactoryId() {
return carFactoryId;
}
public void setCarFactoryId(CarFactoryId carFactoryId) {
this.carFactoryId = carFactoryId;
}
Car car;
Factory factory;
//getters and setters for car and factory
}
CarFactoryId class
@Embeddable
public class CarFactoryId implements Serializable{
private static final long serialVersionUID = -7261887879839337877L;
private Car car;
private Factory factory;
@ManyToOne
public Car getCar() {
return car;
}
public void setCar(Car car) {
this.car = car;
}
@ManyToOne
public Factory getFactory() {
return factory;
}
public void setFactory(Factory factory) {
this.factory = factory;
}
public CarFactoryId(Car car, Factory factory) {
this.car = car;
this.factory = factory;
}
public CarFactoryId() {}
}
Car class
@Entity
public class Car {
@Id
@GeneratedValue
long id;
@Column(name="transmission", nullable = false)
String transmission;
private Set<CarFactory> carFactories = new HashSet<CarFactory>();
@OneToMany(mappedBy = "primaryKey.car",
cascade = CascadeType.ALL)
public Set<CarFactory> getCarFactories() {
return carFactories;
}
...
}
And the same thing for Factory
class, note that there are several ways to define an embedded id
or a composite id
, take a look at:
Note:
In my example I haven't used transmission
field in the composite id but you can use it, you can see the example below:
I emulated your use case and you can find the test on GitHub.
These are the mappings:
@Entity(name = "Car")
public static class Car implements Serializable {
@Id
@GeneratedValue
long id;
@Column(name="transmission", nullable = false)
String transmission;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
Set<CarFactory> factories;
}
@Entity(name = "Factory")
public static class Factory implements Serializable {
@Id
@GeneratedValue
long id;
}
@Entity(name = "CarFactory")
public static class CarFactory implements Serializable {
@Id
@ManyToOne
@JoinColumn(name = "transmission", referencedColumnName = "transmission")
Car car;
@ManyToOne
@Id
Factory factory;
public void setCar(Car car) {
this.car = car;
}
public void setFactory(Factory factory) {
this.factory = factory;
}
}
This is how you add some test data:
doInTransaction(session -> {
Car car = new Car();
car.transmission = "Auto";
Car car1 = new Car();
car1.transmission = "Manual";
Factory factory = new Factory();
session.persist(factory);
session.persist(car);
session.persist(car1);
CarFactory carFactory = new CarFactory();
carFactory.setCar(car);
carFactory.setFactory(factory);
CarFactory carFactory1 = new CarFactory();
carFactory1.setCar(car1);
carFactory1.setFactory(factory);
session.persist(carFactory);
session.persist(carFactory1);
});
And the test works just fine:
@Test
public void test() {
doInTransaction(session -> {
List<CarFactory> carFactoryList = session.createQuery("from CarFactory").list();
assertEquals(2, carFactoryList.size());
});
}
You get an exception because of the following unique constraint:
alter table Car add constraint UK_iufgc8so6uw3pnyih5s6lawiv unique (transmission)
This is the normal behaviour, since a FK must uniquely identify a PK row. Like you can't have more rows with the same PK, you can't have a FK identifier reference more than one row.
You mapping is the problem. You need to reference something else, not the transmision
. You need a unique Car identifier, like a VIN (Vehicle Identification Number), so your mapping becomes:
@Entity(name = "Car")
public static class Car implements Serializable {
@Id
@GeneratedValue
long id;
@Column(name="vin", nullable = false)
String vin;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
Set<CarFactory> factories;
}
@Entity(name = "CarFactory")
public static class CarFactory implements Serializable {
@Id
@ManyToOne
@JoinColumn(name = "vin", referencedColumnName = "vin")
Car car;
@ManyToOne
@Id
Factory factory;
public void setCar(Car car) {
this.car = car;
}
public void setFactory(Factory factory) {
this.factory = factory;
}
}
This way, the vin
is unique and the Child association can reference one and only one parent.
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