我想将从@requestbody获得的数据插入mariadb数据库。目前我可以存储数据没有外键没有任何问题，但现在我需要存储外键，我不知道如何做到这一点。
我的实体现在是这样的：
超类：

package webtoolbackend.Model.Superclass;

import webtoolbackend.Model.Reference.Reference_Category;

import javax.persistence.*;

@MappedSuperclass
public abstract class Category {
private long category_ID;
private String title;
private String description;

public Category() {

}

public Category(long category_ID, String title, String description) {
    this.category_ID = category_ID;
    this.title = title;
    this.description = description;
}

public Category(String title, String description) {
    this.title = title;
    this.description = description;
}

@Id
@Column(name ="Category_ID")
@GeneratedValue(strategy = GenerationType.IDENTITY)
public long getCategory_ID() {
    return category_ID;
}

public void setCategory_ID(long category_ID) {
    this.category_ID = category_ID;
}

@Column(name ="Title")
public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

@Column(name ="Description")
public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}
}

类别：

package webtoolbackend.Model.DE;

import webtoolbackend.Model.Reference.Reference_Category;
import webtoolbackend.Model.Superclass.Category;

import javax.persistence.*;
import java.util.Set;

@Entity
@Table(name="Category_DE")
public class Category_DE extends Category {
private Sector_DE sector_de;
private Set<Question_DE> questions_de;
private Set<Reference_Category> reference_categories;
private long sector_id;

public Category_DE() {
    super();
}

public Category_DE(long category_ID, String title, String description) {
    super(category_ID, title, description);
}
public Category_DE(String title, String description, Sector_DE sector_de) {
    super(title, description);
    this.sector_de = sector_de;
}

public Category_DE(String title, String description, long sector_id) {
    super(title, description);
    this.sector_id = sector_id;
}

@ManyToOne
@JoinColumn(name="Sector_IDFS")
public Sector_DE getSector_de(){
    return sector_de;
}

public void setSector_de(Sector_DE sector_de) {
    this.sector_de = sector_de;
}

@OneToMany(mappedBy="category_de", cascade=CascadeType.ALL)
public Set<Question_DE> getQuestions_de() {
    return questions_de;
}

public void setQuestions_de(Set<Question_DE> questions_de) {
    this.questions_de = questions_de;
}

@OneToMany(mappedBy="category_de", cascade = CascadeType.ALL)
public Set<Reference_Category> getReference_categories() {
    return reference_categories;
}

public void setReference_categories(Set<Reference_Category> reference_categories) {
    this.reference_categories = reference_categories;
}
}

我的控制器：

@CrossOrigin(origins = "*")
@RestController
@RequestMapping("/api")
public class Category_Controller {
@Autowired
Category_Repository category_repository;

@PostMapping("/category-de")
public ResponseEntity<Category> createCategory(@RequestBody Category_DE category_de) {
    try{
        Category_DE savedCategory = category_repository
                .save(new Category_DE(category_de.getTitle(), category_de.getDescription(), category_de.getSector_de()));
        return new ResponseEntity<>(savedCategory, HttpStatus.CREATED);
    }
    catch (Exception e){
        return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}
}

来自requestbody的我的json:

{
"title": "test",
"description": "testDesc",
"sector_de": {
    "sector_id": 1,
    "title": "test"
}
}