Spring MVC / Jackson - weird superstition

I am having a weird problem with Jackson serialization - I have an object Role

that has a nested Permission entity

object, which in turn contains a nested object Metadata

. When these objects are retrieved from Spring MVC @RestController

as a list, Jackson serializes the collection Permission

to a JSON array. The problem is that sometimes the element placed in this array is just an identifier Permission

and not a serialized representation of the object.

Role.class:

@Entity
@Table(name = "t_db_roles")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class,     property = "id", scope = Role.class)
  public class Role implements GrantedAuthority {

  private final static Logger log = LoggerFactory.getLogger(Permission.class);

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

  @Column(name = "role", length = 50)
  private String name;

  @OneToMany(fetch = FetchType.EAGER)
  @JoinTable(name = "t_db_role_permissions",
        joinColumns = {@JoinColumn(name = "roleid", referencedColumnName = "auto_id")},
        inverseJoinColumns = {@JoinColumn(name = "permid", referencedColumnName = "auto_id")}
  )
  private Set<Permission> permissions;

  // getters and setters omitted

}

      

        
        
        
      

    

Permission.class:

@Entity
@Table(name = "t_db_permissions")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Permission.class)
public class Permission implements GrantedAuthority {

    private final static Logger log = LoggerFactory.getLogger(Permission.class);

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

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

    @OneToOne(mappedBy = "permission")
    private Metadata metadata;

}

      

        
        
        
      

    

Metadata.class

@Entity
@Table(name = "t_report_data")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Metadata.class)
public class Metadata {

    @Id
    @Column(name = "id", insertable = false, updatable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "file_name")
    private String fileName;

    @Column(name = "human_name")
    private String humanName;

    @Column(name = "links_to")
    @JsonIgnore
    private Integer linksTo;

    @Column(name = "is_subreport")
    @JsonIgnore
    private Boolean isSubreport;

    @OneToOne(cascade = javax.persistence.CascadeType.ALL, fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "permid")
    private Permission permission;
}

      

        
        
        
      

    

Controller:

@RestController
public class RoleRestController {

    private final static Logger log = LoggerFactory.getLogger(PermissionRestController.class);
    private RoleService roleService;
    private MetadataService metadataService;

    @Autowired
    public void setRoleService(RoleService service) {
        this.roleService = service;
    }

    @Autowired
    public void setMetadataService(ReportMetadataService service) { this.metadataService = service; }

    @RequestMapping(value = "/admin/roles/", method = RequestMethod.GET)
    public List<Role> getRoles() {
        return roleService.getRoles();
    }
}

      

        
        
        
      

    

I'm pretty sure the issue is with serialization - repeating the command List<Role>

in the console works as expected, but here's the JSON returned (note that the first element of the permissions array is an integer, not a JSON object):

{
    "id": 10,
    "name": "ROLE_TESTER",
    "permissions": [
        14,
        {
            "id": 7,
            "name": "ViewDailySettlementSummaryGL",
            "metadata": {
                "id": 41,
                "fileName": "acct_summary_gl.rptdesign",
                "humanName": "Daily Settlement Summary GL",
                "permission": 7
            },
            "authority": "ViewDailySettlementSummaryGL"
        },
        {
            "id": 6,
            "name": "ViewDailySettlementSummary",
            "metadata": {
                "id": 24,
                "fileName": "acct_summary_os.rptdesign",
                "humanName": "Daily Settlement Summary",
                "permission": 6
            },
            "authority": "ViewDailySettlementSummary"
        }
    ],
    "authority": "ROLE_TESTER"
}

      

        
        
        
      

    

I can work around this by handling the serialization Role

manually, but since SpringMVC / Jackson serialization works for other classes in the project, it looks like there must be an issue in those classes that I am missing. Any ideas?