How to create a model, in Spring, from json where the foreign key is referenced as a long attribute?

Question

One Group has many Users:

Group

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonManagedReference;

import javax.persistence.*;
import java.util.Collection;
import java.util.List;

@Entity
@Table(name = "GROUPS")
public class Group {

    @Id
    @Column(name = "ID")
    private Long ID;

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

    //@JsonManagedReference
    @OneToMany(mappedBy = "group"
            //, fetch = FetchType.EAGER
            //, cascade = CascadeType.ALL
    )
    private List<Users> itsUser;

    //getters and setters are omitted for clarity
}

Users

import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonManagedReference;
import com.fasterxml.jackson.annotation.JsonProperty;

import javax.persistence.*;
import static javax.persistence.GenerationType.SEQUENCE;

@Entity
@Table(name = "USERS")
@SequenceGenerator(name = "SEQUENCE_USER_ID",     //my own name in java (unique)
        sequenceName = "GENERATOR_SEQUENCE_USERS",     //in database
        initialValue = 1,
        allocationSize = 1)
public class Users {

    @JsonProperty(value = "id") //these play a role when both reading or writing
    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy=SEQUENCE, generator="SEQUENCE_USER_ID")
    private Long ID;

    @JsonProperty(value = "name")
    @Column(name="NAME")
    private String NAME;

    @JsonProperty(value = "username")
    @Column(name="USERNAME")
    private String USERNAME;

    @JsonProperty(value = "password")
    @Column(name="PASSWORD")
    private String PASSWORD;

    @JsonProperty(value = "email")
    @Column(name="EMAIL")
    private String EMAIL;

    @JsonProperty(value = "picture")    //Now it works with both mypic and picture as json keys
    @Column(name="PICTURE")
    private String PICTURE;

    //@Column(name="GROUP_ID")  //we already have a ManyToOne for this, we cannot repeat it
    @JsonProperty(value = "groups_id")
      //to ignore it in jpa (http://stackoverflow.com/questions/1281952/jpa-fastest-way-to-ignore-a-field-during-persistence)
    private Long itsGroupId;

    @Transient
    public Long getItsGroupId() {
        if(itsGroupId == null) {
            this.itsGroupId = group.getID();
        } else {
            //nop
        }
        return itsGroupId;
    }

    public void setItsGroupId(Long itsGroupId) {
        this.itsGroupId = itsGroupId;
    }

    //@JsonIgnore
    //@JsonProperty(value = "groups_id")
    //@JsonBackReference
    @ManyToOne(optional = false, targetEntity = Group.class)
    @JoinColumn(
            name = "GROUP_ID",  //column name
            referencedColumnName = "ID"   //reference name
    )
    private Group group;

   //getters and setters are omitted for clarity
}

We are using Spring with Spring-data and Jackson to do things automagically but we cannot configure the magic:

We are trying to stick on the following constraints at the same time:

1) Keep the ability to have a reference to the groupId and the ManyToOne relationship group.
This is easy to be achieved by putting @Transient annotation at the groupId because @Column is not allowed since we have already declared the @ManyToOne annotation. You also have to implement the getGroupId method accordingly.

2) Return a json of Users class that contains the groups_id.
This can be implemented by setting the @JsonProperty annotation.

3) Create a user class, and also save it in the database, by a json. The json contains groups_id which has as a value an integer for the foreign key.
This does not work because by setting it @Transient above, then the system refuses to save in the database something that is transient or at least this is how we interpret this exception:

HTTP Status 500 - Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: not-null property references a null or transient value: com.pligor.mvctest.models.Users.group; nested exception is org.hibernate.PropertyValueException: not-null property references a null or transient value: com.pligor.mvctest.models.Users.group

score 1 · Accepted Answer · answered Oct 22 '15 at 12:47

1

On the backend do something like this:

Group group = groupRepository.findById(userResource.getGroupId());
if (group != null) {
   User user = new User(userResource);
   user.setGroup(group);
   userRepository.save();
}

The idea behind this is that you need to fetch the group from the DB, to be able to link it with the newly created User

answered Oct 22 '15 at 12:47

WeMakeSoftware

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we thought that the original configuration was the issue, but we guess there is no other alternative. thank you – George Pligoropoulos Oct 22 '15 at 13:00
Actually you can make it ever simpler than that avoiding a call to the db by creating a Group instance that has only set its ID and all the other fields are null. If you `user.setGroup(group)` and then save it still works but thanks for the answer – George Pligoropoulos Oct 22 '15 at 13:02
we are leaving answering open for a little bit more to allow others provide more elegant solutions if there are any. – George Pligoropoulos Oct 22 '15 at 13:02
1

if you create a new group with only ID field defined you may accidentally delete information about the group (if you save it explicitly, or if your flushMode is set to AUTO) – WeMakeSoftware Oct 22 '15 at 13:04

How to create a model, in Spring, from json where the foreign key is referenced as a long attribute?

Group

Users

1 Answers1