Spring

@Entity
@Table(name = "projects")
@EntityListeners(AuditingEntityListener.class)
@JsonIgnoreProperties(value = {"createdAt", "updatedAt"}, allowGetters = true)
public class Project {

    @Id
    @GeneratedValue
    private Long id;

    @NotBlank
    private String name;

    @ManyToMany(fetch = FetchType.LAZY,
            cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "projects",
            joinColumns = {@JoinColumn(name = "project_id")},
            inverseJoinColumns = {@JoinColumn(name = "user_id")})
    private Set<User> users;

    @Column(nullable = false, updatable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @CreatedDate
    private Date createdAt;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @LastModifiedDate
    private Date updatedAt;
}

@Entity
@Table(name = "users")
@EntityListeners(AuditingEntityListener.class)
@JsonIgnoreProperties(value = {"createdAt", "updatedAt"}, allowGetters = true)
public class User {

    @Id
    @GeneratedValue
    private Long id;

    @NotBlank
    private String name;

    @NotBlank
    private String email;

    @ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, mappedBy = "users")
    private Set<Project> projects;

    @ManyToMany(fetch = FetchType.LAZY,
            cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "users",
            joinColumns = {@JoinColumn(name = "user_id")},
            inverseJoinColumns = {@JoinColumn(name = "device_id")})
    private Set<Device> devices;

    @Column(nullable = false, updatable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @CreatedDate
    private Date createdAt;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @LastModifiedDate
    private Date updatedAt;
}

@Entity
@Table(name = "devices")
@EntityListeners(AuditingEntityListener.class)
@JsonIgnoreProperties(value = {"createdAt", "updatedAt"}, allowGetters = true)
public class Device {

    @Id
    @GeneratedValue
    private Long id;

    @Column(unique = true)
    private String uuid;

    @ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, mappedBy = "devices")
    private Set<User> users;

    @Column(nullable = false, updatable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @CreatedDate
    private Date createdAt;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    @LastModifiedDate
    private Date updatedAt;
}