在数据库上插入实体+外键的正确方法（使用：Mysql，JPA）

Question

I have a question about the right way to make insertion of my entity + foreign key on database(MySQL, JPA). Before asking my question I tried solutions that I found, and I spent days to resolve the problem by myself. I believe I have something wrong :

What I need to do is :

1. I have already data (informations) exists in Site table
2. I have to make the insertion of new sequence in Sequence table
3. I have to make the insertion of new sequence in Sequence table, and association of FK site's (site exists and no need to inserting it again)

The main problem is :

1. When I insert in Sequence Table I have Sequence with FK of Site inserted correctly
2. BUT! The problem is I have also Site insertion in database, so redundant insertion of Site evry time I insert Sequence datas

I just need one insertion of Sequence with association (FK of Site).

Below what's happen on my console :

@Override
        public Site findSiteByName(String Name_Site) {
            List sites = entityManager.createQuery("SELECT s FROM Site s").getResultList();
            for (Site item : sites) {
                if (item.getNom_Site().equals(Name_Site)) {
                    return item;
                }
            }
    
            return null;
        }

Jpa Repository : I first get Site object by name

\n\n    @Override \n        public Site findSiteByName(String Name_Site) {\n            List sites = entityManager.createQuery("SELECT s FROM Site s").getResultList(); \n            for (Site item : sites) {\n                if (item.getNom_Site().equals(Name_Site)) {\n                    return item;\n                } \n            } \n    \n            return null;\n        } \n\n

Jpa method to insert Sequence on data base

@Entity
@Table(name = "Sequences")
public class Sequence {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "Id_Sequence", unique = true, nullable = false)
private long Id_Sequence;
private Date ....;
private Date ....;
private String ....;
private String ....;
private String ....;
private int ....;
private int ....;
private double ....;
private double ....;
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Set<TraceSequence> traceSequences = new HashSet<>();
@ManyToOne(cascade = CascadeType.ALL)
private Site site;

public constructor...

public set..
public get..

My Rest controller :

\n
@GET @Path("/addSeq") @Produces(MediaType.APPLICATION_JSON) @Consumes(MediaType.APPLICATION_JSON) public Sequence addSeq(@Context final UriInfo uriInfo) { Site site = siteService.findSiteByName("Name_Site"); Sequence sequence = sequenceFactory.CreateSequence(new Date(), new Date(), "", "", "", 4, 6, 10, 12); sequence.setSite(site); site.getSequences().add(sequence); sequenceservice.saveSequence(sequence); return null; }
\n

My principal classes are :

\n
@Entity @Table(name = "Sequences") public class Sequence { @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "Id_Sequence", unique = true, nullable = false) private long Id_Sequence; private Date ....; private Date ....; private String ....; private String ....; private String ....; private int ....; private int ....; private double ....; private double ....; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) private Set<TraceSequence> traceSequences = new HashSet<>(); @ManyToOne(cascade = CascadeType.ALL) private Site site; public constructor... public set.. public get..
\n

\n   \n
@Entity \n@Table(name = "Sites") \npublic class Site {
\n
@Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "Id_Site", unique = true, nullable = false) private long Id_Site; private String ...; private boolean ...; private long ...; private Date ...; private Date ...; private String ...; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) private Set<Sequence> sequences = new HashSet<>(); @ManyToOne private ... ...; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) private Set<...> ... = new HashSet<>(); @ManyToOne private ... ...; public constructor... public set.. public get..
\n

Answer 1

Could you try to remove the cascade = CascadeType.ALL in all of the relations? I think the main problem is that CascadeType.PERSIST is cascaded to the child elements. You may have a look here JPA with JTA: Persist entity and merge cascaded child entities

Another thing I would propose is to reduce your table count from 3 to 2. Since you are using a OneToMany -relation, which doesn't need a mapping table like you have now. To achieve this a mappedBy-clause is used within the OneToMany-annotation and an additional JoinColumn-annotation on the ManyToOne site.

@Entity
@Table(name = "Sites")
public class Site {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "Id_Site", unique = true, nullable = false)
    private long Id_Site;
    private String ...;
    private boolean ...;
    private long ...; 
    private Date ...;
    private Date ...;
    private String ...;

    @OneToMany(mappedBy="site", fetch = FetchType.EAGER)
    private Set<Sequence> sequences = new HashSet<>();


@Entity
@Table(name = "Sequences")
public class Sequence {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "Id_Sequence", unique = true, nullable = false)
    private long Id_Sequence;
    private Date ....;
    private Date ....;
    private String ....;
    private String ....;
    private String ....;
    private int ....;
    private int ....;
    private double ....;
    private double ....;

    @OneToMany(fetch = FetchType.EAGER)
    private Set<Sequence> traceSequences = new HashSet<>();

    @ManyToOne(cascade = CascadeType.MERGE)
    @JoinColumn(name = "site_Id_Site", nullable = false)
    private Site site;

EDITED I tried with:

public interface SequenceRepository extends JpaRepository<Sequence, Long> {

}

and

Site site = siteRepository.findOne(1L);

Sequence seq = new Sequence();
seq.setSite(site);
site.getSequences().add(seq);

sequenceRepository.save(seq);

brings

Hibernate: select site0_.id_site...
Hibernate: insert into sequences (site_id_site) values (?)

In classpath I do have spring-data-rest-webmvc-2.5.6.RELEASE.jar .