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
代码语言：yaml复制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
代码语言：java复制@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
代码语言：java复制public interface ActorMapper extends BaseMapper<Actor> {}
public interface FilmActorMapper extends BaseMapper<FilmActor> {}
public interface FilmMapper extends BaseMapper<Film> {}DAO
代码语言：java复制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
代码语言：java复制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
代码语言：java复制@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
