反应式 GraphQL答案

【问题标题】：Reactive GraphQL反应式 GraphQL
【发布时间】：2020-09-18 21:36:49
【问题描述】：

尝试实现响应式 graphql 并遇到一些问题。

pom 依赖，

<dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphql-kickstart-spring-boot-starter-webflux</artifactId>
            <version>7.0.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.graphql-java-kickstart/graphql-kickstart-spring-boot-starter-tools -->
        <dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphql-kickstart-spring-boot-starter-tools</artifactId>
            <version>7.0.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.graphql-java-kickstart/graphiql-spring-boot-starter -->
        <dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphiql-spring-boot-starter</artifactId>
            <version>7.0.1</version>
        </dependency>

架构：-

type Query {

  store(storeId: Int!): Store!

  stores: [Store!]!
}

type Store {
  storeId: Int!
  name: String!
  address: String!
  city: String!
  zip: String!
}

解析器：-

@Component
public class StoreQuery implements GraphQLQueryResolver {

    @Autowired
    private final StoreDao dao;

    public Store store(int storeId) {
        return dao.findById(storeId);
    }

    public List<Store> stores() {
        return dao.findAll();
    }

}

这里，如果我返回 Flux 或 Mono，会出现以下错误。

 "class": "org.springframework.beans.factory.BeanCreationException",
              "msg": "Error creating bean with name 'schemaParser' defined in class path resource [graphql/kickstart/tools/boot/GraphQLJavaToolsAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [graphql.kickstart.tools.SchemaParser]: Factory method 'schemaParser' threw exception; nested exception is java.lang.ClassCastException: class graphql.kickstart.tools.ParameterizedTypeImpl cannot be cast to class java.lang.Class (graphql.kickstart.tools.ParameterizedTypeImpl is in unnamed module of loader 'app'; java.lang.Class is in module java.base of loader 'bootstrap')",


  "class": "java.lang.ClassCastException",
                  "msg": "class graphql.kickstart.tools.ParameterizedTypeImpl cannot be cast to class java.lang.Class (graphql.kickstart.tools.ParameterizedTypeImpl is in unnamed module of loader 'app'; java.lang.Class is in module java.base of loader 'bootstrap')",

所以，尝试以 List 的形式返回。

但是使用阻塞调用将 Flux 转换为 List 也会引发错误，

public List<Store> findAll() {
        return Flux.from(storeCollection.find()).collectList().block();
    }

这里，得到下面的错误。

Exception while fetching data (/stores) : block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-kqueue-2

使用 graphiql 进行测试。

http://localhost:8089/graphiql

【问题讨论】：

您的问题解决了吗？如果可以，请您与 webflux 分享一些 graphql 的参考文档。

标签： graphql graphql-java

【解决方案1】：

正如错误提示，您不能在非阻塞 webflux 中使用阻塞操作。

public Flux<Store> findAll() {
    return Flux.fromIterable(storeCollection.find());
    or
    return Flux.fromStream(storeCollection.find());
}

【讨论】：

【解决方案2】：

您不能在非阻塞 webflux 中使用阻塞操作。如果你使用 kickstart v.7.0.1 你应该返回 CompletableFuture

public CompletableFuture<List<Store>> findAll() {
    return Flux.fromIterable(dao.findAll())
            .collectList()
            .toFuture();
}

【讨论】：