我在使用JPA从mssql的关系表中获取数据时遇到问题

Question

I have a problem fetching data from relational tables with JPA. I believe that my problem is my use of annotations. Im kinda new to this and would love some guidance.

I've had some problem with this before and now that im on vacation I really want to learn Picture entity

@Entity
        @Table(name = "Picture")
        public class Picture {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id")
        @NotNull
        private int id;

        @Column(name = "path")
        @NotNull

        private String path;
        @ManyToOne
        @JoinColumn(name = "portfolio_id", nullable = false)
        private Portfolio portfolio;

and getters, setters.

Portfolio entity

        @Entity
        @Table(name = "Portfolio")
        public class Portfolio {

        @Id
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        @Column(name = "id")
        @NotNull
        private int id;

        @Column(name = "Address")
        @NotNull
        private String address;

        @Column(name = "Description")
        @NotNull
        private String description;

        @Column(name = "Service")
        @NotNull
        private String service;

        @OneToMany(mappedBy = "portfolio")
        private Set<Picture> pictures;

In Portfolio Table I have this object

id        address                 description         service
2         Köpenhamnsvägen 33B     some desc           Full-Staging

and in Picture table i Have this object

id        path                 portfolio_id
1         https://bild.se                 2

When I do a simple get request that fires repository.findAll I get this output:

It's like 5000 rows of this nested object. How come?

Best regards!

Answer 1

It is because you have a bidirectional mapping, so it comes to a recursion. To solve this, just try to add @XmlTransient (JAX-B) or @JsonbTransient/@JsonIgnore (Jackson) to one of the fields. This will make it 'invisible' in the JSON represantation of your backend/RESTful server.

@ManyToOne
@JoinColumn(name = "portfolio_id", nullable = false)
@XmlTransient/@JsonbTransient/@JsonIgnore (try all 3 annotations, since I dont know what implemantation of JAX-RS you are using
private Portfolio portfolio;

or you could do it for the Set:

@OneToMany(mappedBy = "portfolio")
@XmlTransient/@JsonbTransient/@JsonIgnore //again: try them out, I don't know your implementation
private Set<Picture> pictures;

However doing it for both at the same time is not a good idea, since you won't see anything in the request as a result.