Null values are inserted in the foreign key fields with Hibernate

Question

I have a Question Entity and Tag entity with getter, setter methods and a OneToMany relationship from question to tag and a OneToOne relationship from question to user

public class Question {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;

    @Column(name="title")
    private String title;

    @Column(name="body")
    private String body;

    @Temporal(TemporalType.DATE)
    @Column(name="date_created")
    private Date date_created;

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="user_id")
    private User user;

    @OneToMany(cascade=CascadeType.ALL)
    @JoinColumn(name="tag_id")
    private Tag tag;

    @Column(name="answer_count")
    private int answer_count;

    @Column(name="view_count")
    private int view_count;

    public Question() {

}

Tag entity

public class Tag {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;

    @Column(name="name")
    private String name;

    @Column(name="username")
    private String username;

    @Temporal(TemporalType.DATE)
    @Column(name="date_created")
    private Date date_created;

    public Tag() {

}

When I try to insert a question using Postman with the following details:

{
    "title": "stefanyyyxx",
    "body": "stefandoyee44",
    "date_created": "2019-02-27",
    "user_id" : 1,
    "tag_id": 1,
    "answer_count": 0,
    "view_count": 0
}

QuestionRepository.java:

@Override
public void save(Question theQuestion) {

    // get the current hibernate session
    Session currentSession = entityManager.unwrap(Session.class);

    // save employee
    currentSession.saveOrUpdate(theQuestion);
}

Null values are being inserted for user_id and tag_id though I used JoinColumn() .

MySQL:

Answer 1

As @Karol Dowbecki Suggested,

convert the JSON to DTO object and use that DTO to get the User , Tag Entities from their respective repositories .

Finally create the Question entity object and store it.

Question Entity

@Entity
@Table(name = "question")
public class Question {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "title")
    private String title;

    @Column(name = "body")
    private String body;

    @Temporal(TemporalType.DATE)
    @Column(name = "date_created")
    private Date dateCreated;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "user_id")
    private User user;

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "tag_id")
    private Set<Tag> tag;

    @Column(name = "answer_count")
    private int answerCount;

    @Column(name = "view_count")
    private int viewCount;

}

User Entity

@Entity
@Table(name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

}

Tag Entity

@Entity
@Table(name = "tag")
public class Tag {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "username")
    private String username;

    @Temporal(TemporalType.DATE)
    @Column(name = "date_created")
    private Date dateCreated;

}

DTO Class

public class QuestionDTO {

    private Long id;

    private String title;

    private String body;

    private Date dateCreated;

    private Long user;

    private Long tag;

    private int answerCount;

    private int viewCount;
}

Test Class

@Service
public class TestService {

    @Autowired
    private QuestionRepository questionRepository;

    @Autowired
    private UserRepository userRepository;

    @Autowired
    private TagRepository tagRepository;

    public void addQuestion(QuestionDTO dto) {
        Tag tag = null;
        User user = null;
        Question question = null;

        Set<Tag> tags = null;

        tag = tagRepository.findById(dto.getTag());

        tags = new HashSet<>();
        tags.add(tag);

        user = userRepository.findById(dto.getUser());

        question = new Question();
        question.setTag(tags);
        question.setUser(user);
        question.setId(dto.getId());
        question.setBody(dto.getBody());
        question.setTitle(dto.getTitle());
        question.setViewCount(dto.getViewCount());
        question.setAnswerCount(dto.getAnswerCount());
        question.setDateCreated(dto.getDateCreated());

        questionRepository.save(question);

    }
}

NOTE : The relation between Question and Tag are in OneToMany you have to use Collection type.

Answer 2

You have a mismatch between JSON and @Entity structure. JSON contains numeric identifiers while the @Entity contains actual objects representing relationships. You most likely should introduce a separate DTO class to map this JSON while in @Repository you should load User and Tag objects based on their id or create new ones. You already have CascadeType.ALL so Hibernate will cascade the persist operation.

Generally the controller layer should be separate from repository layer unless you are doing something very, very simple. This helps to evolve the service without changing the API contract eg adding new columns for auditing changes. By exposing the @Entity as DTO you make your life harder down the road.

Answer 3

You should add referencedColumnName in your Child Entity Foreign Key Column

referencedColumnName="your primaray key column name"

EDIT:

referencedColumnName

• The name of the column referenced by this foreign key column.
• When used with entity relationship mappings other than the cases described here, the referenced column is in the table of the target entity.
• When used with a unidirectional OneToMany foreign key mapping, the referenced column is in the table of the source entity.
• When used inside a JoinTable annotation, the referenced key column is in the entity table of the owning entity, or inverse entity if the join is part of the inverse join definition.
• When used in a CollectionTable mapping, the referenced column is in the table of the entity containing the collection.
• Default (only applies if single join column is being used): The same name as the primary key column of the referenced table.

Asset is Parent Entity and AssetDetails is Child Entity Here I have taken OneToOne Relationship

Asset.java

@Entity
@Table(name="asset")
public class Asset {

    @Id
    @GeneratedValue
    @Column(name="assetid")
    private BigInteger assetid;

    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "asset")
    @JsonBackReference
    private AssetDetails assetDetails;

     public AssetDetails getAssetDetails() {
        return assetDetails;
    }

    public void setAssetDetails(AssetDetails assetDetails) {
        this.assetDetails = assetDetails;
        assetDetails.setAsset(this);
    }

    public Asset(your fields, AssetDetails assetDetails) {
        super();
        // your fields
        this.assetDetails = assetDetails;
        this.assetDetails.setAsset(this);
    }

    public Asset() {
        super();
    }

    public BigInteger getAssetid() {
        return assetid;
    }

    public void setAssetid(BigInteger assetid) {
        this.assetid = assetid;
    }
}

AssetDetails.java

@Entity
@Table(name="assetDetails")
public class AssetDetails {

    @Id
    @GeneratedValue
    private BigInteger assetdetailid;

    @JoinColumn(name = "assetid",nullable = false, updatable = false,referencedColumnName="assetid")
    @OneToOne(cascade=CascadeType.ALL)
    @JsonManagedReference
    private Asset asset;

    public Asset getAsset() {
        return asset;
    }

    public void setAsset(Asset asset) {
        this.asset = asset;
    }

    public AssetDetails(your fields,Asset asset) {
        super();
        //your fields
        this.asset = asset;
    }   
}