Entity creates useless id field - json

Question

I have a CrudRepository with two entities.
Problem: The characteristic entity always creates an additional id field in the database but does not select the correct characteristic_id field to generate JSON.
machine entity
machine_id || name || description
characteristic entity
characteristic_id || machine_id || name || description || type || value
Question: Why does the characteristic entity always create an id field named id and does not use the definded filed characteristic_id?
JSON
How the entity manipulates the database layout:
Machine entity
#Entity
#Table(name = "maschine")
public class Machine {
private int machine_id;
private String name;
private String description;
private Set<Characteristic> characteristics;
#OneToMany(fetch = FetchType.EAGER, mappedBy = "machine", cascade = CascadeType.ALL)
public Set<Characteristic> getCharacteristics() {
return characteristics;
}
public void setCharacteristics(Set<Characteristic> characteristics){
this.characteristics = characteristics;
}
public Machine(){}
public Machine(String name, String description){
this.name = name;
this.description = description;
}
#Override
public String toString() {
return "Machine [id=" + machine_id + ", name=" + name + ", description=" + description + "]";
}
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="id")
public int getId() {
return machine_id;
}
public void setId(int machine_id) {
this.machine_id = machine_id;
}
#Column(name="name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#Column(name="description")
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}
Characteristic entity
#Entity
#Table(name = "characteristic")
public class Characteristic {
private int characteristic_id;
private String name;
private String description;
private int type;
private int value;
private Machine machine;
#ManyToOne
#JoinColumn(name="machine_id")
public Machine getMachine(){
return machine;
}
public void setMachine(Machine machine){
this.machine = machine;
}
public Characteristic() {}
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="id")
public int getCharacteristic_Id() {
return characteristic_id;
}
public void setCharacteristic_Id(int characteristic_id) {
this.characteristic_id = characteristic_id;
}
#Column(name="name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#Column(name="description")
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
#Column(name="type")
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
#Column(name="value")
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
#Override
public String toString() {
return "Characteristic [id=" + characteristic_id + ", name=" + name + ", description=" + description + ", type=" + type
+ ", value=" + value + "]";
}
}
My CrudRepository to interact with the database:
public interface MachineRepository extends CrudRepository<Machine, Integer>{
}
My Controller:
#RestController
public class HomeController {
private final MachineRepository machineRepository;
#Autowired
HomeController(MachineRepository machineRepository) {
this.machineRepository = machineRepository;
}
#RequestMapping(value = "/machine", method = RequestMethod.GET)
Collection<Machine> readMachines(){
return (Collection<Machine>) machineRepository.findAll();
}
}
This is all code I have written for the database operations..

Answer 1

Change to this code
#Id
#GeneratedValue
#Column(name="id", nullable = false)
public int getCharacteristic_id() {
return characteristic_id;
}

Answer 2

By default as you have not specified the column name in your configuration hibernate will use the name of the getter methode without "get" part as the column name in the table. Below is the configuration in your Characteristic Entity
#Id
#GeneratedValue
public int getId() {
return characteristic_id;
}
As you have not specified any explicit column name for the memeber characteristic_id , hibernate by default chooses Id (removing get from the getId() method) as the column name for the member. And hence it always creates a column named Id for you characteristics_id member .
In order to force hibernate to use characteristic_id as the column name , you can use #Column annotation and provide the column name as characteristics_id
apart from the #Id and #GeneratedValue you are using to mark the getter.
#Id
#GeneratedValue
#Column(name="characteristic_id")
public int getId() {
return characteristic_id;
}
or you can change the name of getter and setter as below
#Id
#GeneratedValue
public int getCharacterisitc_id() {
return characteristic_id;
}
public void setCharacterisitc_id(int characteristic_id) {
this.characteristic_id = characteristic_id;
}