GraphQL实践5——Netflix Dgs Graphql懒加载

F嘉阳 • 2023-01-02 • 云技术社区 • 283 阅读

问题背景

在graphql中，需要查询的字段由调用方传递，如果此时存在关联表才能获取的字段，但前端不需要该字段的时候，默认查询所有字段会带来较大开销

例如

type Actor {
    actorId: Int!
    firstName: String!
    lastName: String!
    lastUpdate: String
}

type Film {
    filmId: Int!
    title: String!
    description: String
    actors: [Actor]
}

type Query {
    filmList: [Film]
}

解决方案——懒加载

DGS框架中支持配置调用方传递了指定字段才读取对应的数据

配置懒加载

增加实体定义，模拟嵌套实体

Mybatis Plus配置

扫描配置

@Configuration
@MapperScan("top.fjy8018.graphsqldemo.mapper")
public class MybatisPlusConfig {
}

实体

表结构还是使用sakila样例数据库的表

@Data
public class Actor implements Serializable {

    @Serial
    private static final long serialVersionUID = 1L;

    /**
     * 联系人ID
     */
    @TableId(type = IdType.AUTO)
    private Integer actorId;

    private String firstName;

    private String lastName;

    private Date lastUpdate;

}

@Data
public class Film implements Serializable {

   @Serial
   private static final long serialVersionUID = 1L;

   /**
    * 联系人ID
    */
   @TableId(type = IdType.AUTO)
   private Integer filmId;

   private String title;

   private String description;

   private Integer releaseYear;

   private Integer languageId;

   private Integer originalLanguageId;

   private Integer rentalDuration;

   private BigDecimal rentalRate;

   private Integer length;

   private BigDecimal replacementCost;

   private String rating;

   private String specialFeatures;

   private Date lastUpdate;
}

@Data
public class FilmActor implements Serializable {

   @Serial
   private static final long serialVersionUID = 1L;

   /**
    * 联系人ID
    */
   @TableId(type = IdType.AUTO)
   private Integer actorId;

   private Integer filmId;

   private Date lastUpdate;
}

Mapper

public interface ActorMapper extends BaseMapper<Actor> {}
public interface FilmActorMapper extends BaseMapper<FilmActor> {}
public interface FilmMapper extends BaseMapper<Film> {}

DAO

public interface ActorRepository extends IService<Actor> {
}
public interface FilmActorRepository extends IService<FilmActor> {
   List<FilmActor> listByFilmId(@Size.List({@Size(min = 1, message = "至少要有一个元素")}) List<Integer> filmIds);
}
public interface FilmRepository extends IService<Film> {
}
@Validated
@Repository
@RequiredArgsConstructor
public class ActorRepositoryImpl extends ServiceImpl<ActorMapper, Actor> implements ActorRepository {
}
@Validated
@Repository
@RequiredArgsConstructor
public class FilmActorRepositoryImpl extends ServiceImpl<FilmActorMapper, FilmActor> implements FilmActorRepository {
   @Override
   public List<FilmActor> listByFilmId(List<Integer> filmIds) {
      return lambdaQuery().in(FilmActor::getFilmId, filmIds).list();
   }
}
@Validated
@Repository
@RequiredArgsConstructor
public class FilmRepositoryImpl extends ServiceImpl<FilmMapper, Film> implements FilmRepository {
}

Service

多表查询聚合逻辑

public interface ActorService {
   List<Actor> listByFilmId(Integer filmId);
}

@Slf4j
@Service
@RequiredArgsConstructor
public class ActorServiceImpl implements ActorService {

   private final ActorRepository actorRepository;

   private final FilmActorRepository filmActorRepository;

   @Override
   public List<Actor> listByFilmId(Integer filmId) {
      List<FilmActor> filmActors = filmActorRepository.listByFilmId(List.of(filmId));
      if (CollectionUtils.isEmpty(filmActors)) {
         return Collections.emptyList();
      }
      List<Integer> actorIds = filmActors.stream().map(FilmActor::getActorId).toList();
      return actorRepository.listByIds(actorIds);
   }
}

Graphql 查询解析器

@DgsComponent
@RequiredArgsConstructor
public class FilmDataFetcher {

   private final FilmRepository filmRepository;

   private final ActorService actorService;

   @DgsQuery
   public Collection<Film> filmList() {
      return filmRepository.list();
   }

   @DgsData(parentType = "Film")
   public List<Actor> actors(DgsDataFetchingEnvironment dfe) {
      Film film = dfe.getSource();
      return actorService.listByFilmId(film.getFilmId());
   }

   @DgsQuery
   public Film findOneFilm(@InputArgument Integer id) {
      return filmRepository.getById(id);
   }
}

增加DgsDataFetchingEnvironment入参，DGS会自动获取请求上下文参数

此处定义即为传入了actors参数才执行该方法获取对应的Actor集合，实现懒加载

测试

访问http://localhost:8080/graphiql即可看到在线查询页面

不访问Actor

image-20221027222611945.png

此时可以看到日志输出，没有查询Actor表

image-20221027222636357.png

访问Actor

image-20221027222705715.png

此时DSG会执行N+1查询Actor表，性能损耗非常大

image-20221027222731234.png

总结

对于表关联，开销较大字段，都可以使用DSG懒加载实现性能优化，但此时还是存在N+1查询性能问题，将在后面使用DataLoader优化

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GraphQL实践5——Netflix Dgs Graphql懒加载
在graphql中，需要查询的字段由调用方传递，如果此时存在关联表才能获取的字段，但前端不需要该字段的时候，默认查询所有字段会带来较大开销
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