Modelling nested entities

Question

Being new to hibernate/jpa i am facing difficulty on how to model the nested entities correctly, my requirment, user -> have many roles -> each role have many permissions

Each permission for a role needs to be persisted as separate row in table. And, need to have separate tables for users and theirs roles; again each role of a user need to be persisted as a separate row in table. I wrote the below; but this is not allowing me to create new users with already defined roles...

@Entity
@Table(name = "users")
public class User implements Serializable {

    @Id
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(name = "UUID",strategy = "org.hibernate.id.UUIDGenerator")
    public UUID id;

    @Column(name = "username")
    public String name;

    @Column(name = "password")
    public String password;

    @OneToMany(cascade = CascadeType.ALL, mappedBy="user")
    @LazyCollection(LazyCollectionOption.FALSE)
    public List<UserRole> roles;
}

@Entity
@Table(name = "user_roles")
public class UserRole implements Serializable {

    @Id
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(name = "UUID",strategy = "org.hibernate.id.UUIDGenerator" )
    public UUID id;

    @ManyToOne
    @JoinColumn(name="username", nullable=false, referencedColumnName = "username")
    public User user;

    @Column(name = "role_name")
    public String roleName;

    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})
    @JoinColumn(name = "role_name", referencedColumnName = "role_name")
    public List<RolePermission> permissions;

}

@Entity
@Table(name = "roles_permissions")
public class RolePermission implements Serializable {

    @Id
    @Column(name = "role_name")
    public String roleName;

    @Id
    @Column(name = "permission")
    public String permission;
}

Get the below error,

2019-03-06 21:25:22.643 ERROR 48896 --- [nio-8090-exec-3] o.h.engine.jdbc.spi.SqlExceptionHelper : ERROR: duplicate key value violates unique constraint "uk_40fvvy071dnqy9tywk6ei7f5r" Detail: Key (role_name)=(owner) already exists.

karts karts · Accepted Answer · 2019-03-10T08:04:04

Got it working after correctly modelling UserRole, below is my new entity class for UserRole,

@Entity
@Table(name = "user_roles")
public class UserRole implements Serializable {

    @Id
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(
            name = "UUID",
            strategy = "org.hibernate.id.UUIDGenerator"
    )
    public UUID id;

    @ManyToOne
    @JoinColumn(name="username", nullable=false, referencedColumnName = "username")
    public User user;

    @Column(name = "role_name")
    public String roleName;

    @ManyToMany
    @JoinTable(name = "roles_permissions",joinColumns = @JoinColumn(name = "role_name"))
    public List<RolePermission> permissions;

}

Modelling nested entities

1 Answers