如何防止模型映射器在springdatajpa中不映射延迟加载的集合？

Question

我正在使用Spring Boot、Spring Data JPA和mysql制作一个Restapi。我有用户和角色实体。用户可以有很多角色，角色可以有很多用户。我是ModelMapper依赖项，用于将实体转换为DTO。

我已将角色集合获取类型设置为惰性。但是ModelMapper正在用户实体上调用getRoles（）方法。如何停止它。

注意:用户和用户数据有相同的字段。

用户类别:

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

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String username;
private String password;
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(
        name = "user_roles",
        joinColumns = @JoinColumn(name = "user_id",referencedColumnName = "id"),
        inverseJoinColumns = @JoinColumn(name = "role_id",referencedColumnName = "id")
)
private Set<Role> roles;
}

角色类别:

@Entity
@Table(name = "roles")
public class Role  {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String roleName;
}

用户服务类：

@Service
@Transactional
public class UserService {

@Autowired
private ModelMapper mapper; 
@Autowired
private UserRepository userRepository;

public UserDTO find(Integer id){
   User user = userRepository.findById(id).get();
   return mapper.map(user,UserDTO.class);
}
}

Answer 1

您可以应用条件跳过操作。https://stackoverflow.com/a/38729404/2039546

ModelMapper modelMapper = new ModelMapper();
TypeMap<User, UserDTO> typeMap = modelMapper
        .createTypeMap(User.class, UserDTO.class);
// Create empty list condition for JPA.
Condition<Object, Object> emptyListCondition = mc ->
        (!(mc.getSource() instanceof PersistentCollection) 
                || ((PersistentCollection) mc.getSource())
                .wasInitialized());
// Add mappings.
typeMap.addMappings(mapper -> mapper
        .when(emptyListCondition)
        .map(User::getRoles, UserDTO::setRoles));

// Test.
UserDTO userDTO = modelMapper.map(user, UserDTO.class);

Answer 2

你必须声明一个跳过属性。

例：

TypeMap<Game, GameDTO> propertyMapper = this.mapper.createTypeMap(Game.class, GameDTO.class);
propertyMapper.addMappings(mapper -> mapper.skip(GameDTO::setId));

参考： https://www.baeldung.com/java-modelmapper