@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToMany(
            cascade = {CascadeType.PERSIST, CascadeType.MERGE},
            fetch = FetchType.EAGER)
    @JoinTable(
            name = "user_role",
            joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles;

    // other fields, constructors, getters/setters
}

@Entity
public class Role {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToMany(mappedBy = "roles")
    private Set<User> users;

    // other fields, constructors, getters/setters
}

@Entity
public class Order {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne(optional = false)
    @JoinColumn(name = "user_id")
    private User submitter;
    @ManyToOne(optional = false)
    @JoinColumn(name = "user_id")
    private User approver;

    // other fields, constructors, getters/setters
}

@Entity
public class Order {

    // id, submitter, approver fields, see in previous snippet

    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL)
    private Set<OrderItem> items;

    // other fields, constructors, getters/setters
}

@Entity
public class OrderItem {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "order_item_id")
    private Order order;

    // other fields, constructors, getters/setters
}

@Entity
public class Order {

    // fields from previous snippets

    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL)
    private Set<OrderAttachment> attachments;

    // other fields, constructors, getters/setters
}

@Entity
public class OrderAttachment {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String fileName;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "order_attachment_id")
    private Order order;

    @Lob
    @Basic(fetch = FetchType.LAZY)
    private byte[] file;
}