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GraphQL入门总体创建教程

2022-11-13 14:10

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简介

因为目前做的项目查询提供的接口都使用GraphQL替代典型的REST API，所以有必要去对它进行了解和源码的阅读。本篇主要大致了解下GraphQL。

一种用于API的查询语言，让你的请求数据不多不少。前端按需获取，后端动态返回（不需要的数据不会返回甚至不会查库），对比起典型的REST API将更加灵活，后端代码提供可选能力。如果增加新的字段应用不想处理这部分数据可以不用区分版本。

后端确定哪些接口行为是被允许的，前端按需获取数据，让你的请求数据不多不少。

详细的介绍可以参考官方首页配合动图更加清晰。

简单示例

最好使用Spring Initializr去创建一个新的项目，不会产生一些冲突。

maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.graphql-java.tutorial</groupId>
    <artifactId>book-details</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>book-details</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.graphql-java/graphql-java -->
        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java</artifactId>
            <version>11.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.graphql-java/graphql-java-spring-boot-starter-webmvc -->
        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java-spring-boot-starter-webmvc</artifactId>
            <version>1.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>26.0-jre</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    <repositories>
        <repository>
            <id>central</id>
            <name>aliyun maven</name>
            <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
            <layout>default</layout>
            <!-- 是否开启发布版构件下载 -->
            <releases>
                <enabled>true</enabled>
            </releases>
            <!-- 是否开启快照版构件下载 -->
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>
</project>

Schema

在class="lazy" data-src/main/resources中创建schema.graphqls文件：

type Query {
    bookById(id: ID): Book
}
type Book {
    id: ID
    name: String
    pageCount: Int
    author: Author
}
type Author {
    id: ID
    firstName: String
    lastName: String
}

可以看到定义了一个bookById查询，用于根据id查询书籍，书籍中包含id、name、pageCount、author属性，其中author是一个复合类型所以定义了type Author。

上面显示的用于描述schema的特定于域的语言称为schema定义语言或SDL。更多细节可以在这里找到。

解析schema并关联对应的fetchers

一旦我们有了这个文件，我们需要通过读取文件并解析它并且添加代码来为它获取数据使它“栩栩如生”。

package com.graphqljava.tutorial.bookdetails;
import com.google.common.base.Charsets;
import com.google.common.io.Resources;
import graphql.GraphQL;
import graphql.schema.GraphQLSchema;
import graphql.schema.idl.RuntimeWiring;
import graphql.schema.idl.SchemaGenerator;
import graphql.schema.idl.SchemaParser;
import graphql.schema.idl.TypeDefinitionRegistry;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
import java.io.IOException;
import java.net.URL;
import static graphql.schema.idl.TypeRuntimeWiring.newTypeWiring;
@Component
public class GraphQLProvider {
    private GraphQL graphQL;
    
    @Bean
    public GraphQL graphQL() {
        return graphQL;
    }
    @PostConstruct
    public void init() throws IOException {
        //使用Resources读取graphqls文件
        URL url = Resources.getResource("schema.graphqls");
        //拿到graphqls文件内容
        String sdl = Resources.toString(url, Charsets.UTF_8);
        GraphQLSchema graphQLSchema = buildSchema(sdl);
        this.graphQL = GraphQL.newGraphQL(graphQLSchema).build();
    }
    @Autowired
    GraphQLDataFetchers graphQLDataFetchers;
    
    private GraphQLSchema buildSchema(String sdl) {
        TypeDefinitionRegistry typeRegistry = new SchemaParser().parse(sdl);
        RuntimeWiring runtimeWiring = buildWiring();
        SchemaGenerator schemaGenerator = new SchemaGenerator();
        return schemaGenerator.makeExecutableSchema(typeRegistry, runtimeWiring);
    }
    
    private RuntimeWiring buildWiring() {
        return RuntimeWiring.newRuntimeWiring()
                .type(newTypeWiring("Query")
                        .dataFetcher("bookById", graphQLDataFetchers.getBookByIdDataFetcher()))
                .type(newTypeWiring("Book")
                        .dataFetcher("author", graphQLDataFetchers.getAuthorDataFetcher()))
                .build();
    }
}

package com.graphqljava.tutorial.bookdetails;
import com.google.common.collect.ImmutableMap;
import graphql.schema.DataFetcher;
import org.springframework.stereotype.Component;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
@Component
public class GraphQLDataFetchers {
    
    private static List<Map<String, String>> books = Arrays.asList(
            ImmutableMap.of("id", "book-1",
                    "name", "Harry Potter and the Philosopher's Stone",
                    "pageCount", "223",
                    "authorId", "author-1"),
            ImmutableMap.of("id", "book-2",
                    "name", "Moby Dick",
                    "pageCount", "635",
                    "authorId", "author-2"),
            ImmutableMap.of("id", "book-3",
                    "name", "Interview with the vampire",
                    "pageCount", "371",
                    "authorId", "author-3")
    );
    
    private static List<Map<String, String>> authors = Arrays.asList(
            ImmutableMap.of("id", "author-1",
                    "firstName", "Joanne",
                    "lastName", "Rowling"),
            ImmutableMap.of("id", "author-2",
                    "firstName", "Herman",
                    "lastName", "Melville"),
            ImmutableMap.of("id", "author-3",
                    "firstName", "Anne",
                    "lastName", "Rice")
    );
    
    public DataFetcher getBookByIdDataFetcher() {
        return dataFetchingEnvironment -> {
            // 获得查询筛选参数
            String bookId = dataFetchingEnvironment.getArgument("id");
            return books
                    .stream()
                    .filter(book -> book.get("id").equals(bookId))
                    .findFirst()
                    .orElse(null);
        };
    }
    
    public DataFetcher getAuthorDataFetcher() {
        return dataFetchingEnvironment -> {
            //获得上级对象
            Map<String, String> book = dataFetchingEnvironment.getSource();
            //根据上级对象找到关联id（相当于外键）
            String authorId = book.get("authorId");
            return authors
                    .stream()
                    .filter(author -> author.get("id").equals(authorId))
                    .findFirst()
                    .orElse(null);
        };
    }
}

DataFetchers

对于GraphQL Java服务器来说，最重要的概念可能是DataFetcher：DataFetcher在执行查询时获取一个字段的数据。

GraphQL Java在执行查询时，会为查询中遇到的每个字段调用相应的DataFetcher。DataFetcher是函数接口，函数具有一个参数为DataFetchingEnvironment类型。

public interface DataFetcher<T> {
T get(DataFetchingEnvironment dataFetchingEnvironment) throws Exception;
}

Default DataFetchers

如上我们实现了两个DataFetchers。如上所述，如果你不指定一个，PropertyDataFetcher则是被默认使用。比如上面的例子中Book.id，Book.name，Book.pageCount,Author.id，Author.firstName和Author.lastName都有一个PropertyDataFetcher与之关联。

PropertyDataFetcher尝试以多种方式查找Java对象的属性。如果是java.util.Map，简单的通过key查找。这对我们来说非常好，因为book和author Maps的keys与schema中指定的字段相同。