I'm about to design my rest API. I wonder how can I handle objects such as one below:
@Entity
public class Foo {
@ManyToMany
private Set<Bar> barSet;
@OneToMany
private Set<Zzz> zzzSet;
}
As you see object I want to expose to my rest API consists of other entity collections. I'm using Spring 4 and Jackson. Is it possible to return objects like one above - or do I have to create classes with primitive values only?
Yes, it is possible but you have to handle 2 problems :
1) at serialization, Jackson will call the getter Foo.getBarSet(). This will crash because by default, Hibernate returns lazy collections for @OneToMany and @ManyToMany relationships.
If you don't need them, annotate them with @JsonIgnore :
@Entity
public class Foo {
@JsonIgnore
@ManyToMany
private Set<Bar> barSet;
@JsonIgnore
@OneToMany
private Set<Zzz> zzzSet;
}
If you need them, you must tell hibernate to load them. For example, you can annotate @ManyToMany and @OneToMany with fetch = FetchType.EAGER (It is not the only solution btw) :
@Entity
public class Foo {
@ManyToMany(fetch = FetchType.EAGER)
private Set<Bar> barSet;
@OneToMany(fetch = FetchType.EAGER)
private Set<Zzz> zzzSet;
}
2) It can also cause some infinite loops :
Foo.getBarSet()Bar.getFoo()Foo.getBarSet()This can be handled with @JsonManagedReference and @JsonBackReference :
@Entity
public class Foo {
@JsonManagedReference
@OneToMany
private Set<Zzz> zzzSet;
And on the other side :
@Entity
public class Zzz {
@JsonBackReference
private Foo parent;
}
