问题背景
上一篇文章提到，使用List查询每次都返回全量数据，而实际场景更多使用分页查询，graphql-java提供Connection实现游标分页，在Dgs也有对应功能扩展Relay Pagination
集成Relay Pagination
新增依赖
代码语言：txt复制 <dependency>
<groupId>com.netflix.graphql.dgs</groupId>
<artifactId>graphql-dgs-pagination</artifactId>
</dependency>Mybatis Plus 配置分页插件
代码语言：txt复制@Configuration
@MapperScan("top.fjy8018.graphsqldemo.mapper")
public class MybatisPlusConfig {
/**
* 分页插件配置
*
* @return
*/
@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
PaginationInnerInterceptor pageConfig = new PaginationInnerInterceptor(DbType.MYSQL);
interceptor.addInnerInterceptor(pageConfig);
return interceptor;
}
}Relay Pagination配置
代码语言：txt复制type Query {
actorList: [Actor]
findOneActor(id : Int!): Actor
filmList(current: Int!,size: Int!): FilmConnection
findOneFilm(id : Int!): Film
}
type Actor {
actorId: Int!
firstName: String!
lastName: String!
lastUpdate: String
}
type Film @connection {
filmId: Int!
title: String!
description: String
releaseYear: Int
languageId: Int!
originalLanguageId: Int
rentalDuration: Int
rentalRate: Float
length: Int
replacementCost: Float
rating: String
specialFeatures: String
lastUpdate: String
actors: [Actor]
}@connection和XXXConection已经由graphql-java底层框架自动生成，无需手动定义
类型转换器
代码语言：txt复制public interface ConnectionAssembler {
/**
* mybatis plus分页对象转为Connection
*
* @param page 分页对象
* @param <T> 泛型
* @return Connection
*/
static <T> Connection<T> convert(IPage<T> page) {
AtomicInteger index = new AtomicInteger();
List<Edge<T>> defaultEdges = Stream.ofNullable(page.getRecords())
.flatMap(Collection::stream)
.map(e -> (Edge<T>) new DefaultEdge<>(e, new DefaultConnectionCursor(String.valueOf(index.incrementAndGet()))))
.toList();
return new DefaultConnection<>(defaultEdges,
new DefaultPageInfo(new DefaultConnectionCursor(String.valueOf(page.getCurrent())),
new DefaultConnectionCursor(String.valueOf(page.getPages())),
page.getCurrent() > 1,
page.getCurrent() < page.getPages()));
}
}Graphql解析配置
代码语言：txt复制 @DgsQuery
public Connection<Film> filmList(@InputArgument("current") Integer current,
@InputArgument("size") Integer size,
DgsDataFetchingEnvironment dfe) {
IPage<Film> page = new PageDTO<>(current, size);
IPage<Film> pageResult = filmRepository.page(page);
return ConnectionAssembler.convert(pageResult);
}将List查询改为返回Connection即可
测试
访问http://localhost:8080/graphiql即可看到在线查询页面
image-20221027224826034.png查看查询数量，确认是按照分页查询
image-20221027224859609.png总结
到此，DSG核心功能尝试基本完成，基本实现常用的Rest功能，同时集成方便，而且官方文档清晰，但目前开源社区还没有太多的基于DSG的系统集成样例，还需要在实践中评估摸索。
thoughtworks也从2016年开始关注graphql，目前给出的建议也是“评估”，可以进行小规模尝试并在合适的时候推广
We've seen many successful GraphQL implementations on our projects. We've seen some interesting patterns of use too, including GraphQL for server-side resource aggregation. That said, we've concerns about misuse of this framework and some of the problems that can occur. Examples include performance gotchas around N 1 queries and lots of boilerplate code needed when adding new models, leading to complexity. There are workarounds to these gotchas such as query caching. Even though it's not a silver bullet, we still think it's worth assessing as part of your architecture.
