Question

I am trying to get the following type of mapping to work

Table event has the following columns:
id (PK)
prodgroup
errandtype

table errandtype : errandtype

table prodgroup: prodgroup

I have corresponding JPA classes

@Entity
@Table(name="event")
public class MyEvent {
    @Id
    int id;

    // what mapping should go here?
    Prodgroup prodgroup;

    // what mapping should go here?
    ErrandType errandtype;
} 

@Entity
public class Prodgroup {
    @Id
    private String prodgroup;
}

@Entity
public class ErrandType {
    @Id
    private String errandtype;
}

Ok so questions are marked as comments in the code but I’ll try to be explicit anyway.

In the above example I want my Prodgroup and ErrandType fields in the MyEvent class to be set to corresponding Prodgroup and Errandtype instances

I have tried @OneToOne relationships with @joincolumns and with mappedby attribute, but I just can’t get it working and I’ve lost all sense of logical approach. My grasp of JPA entity mapping is clearly weak.

So can anyone bring some clarity?

Answer 1

It should be:

@Entity
@Table(name="event")
public class MyEvent {
    @Id
    int id;

    // what mapping should go here?
    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "prodgroup_id", insertable = true, updatable = true)
    Prodgroup prodgroup;

    // what mapping should go here?
    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "errandtype_id", insertable = true, updatable = true)
    ErrandType errandtype;
} 

@Entity
public class Prodgroup {
    @Id
    private String prodgroup;
}

@Entity
public class ErrandType {
    @Id
    private String errandtype;
}

FetchType Eager means the object will be always loaded (would be “Lazy” by default if not specified).
CascadeType.ALL means mearge/persist/remove will be also done to linked tables.

Sebastian