练习Practice
动手做Get your hands on it
练习跟着课文走 —— 每节课尾都有本课的练习。这一页是全部练习的总库，想集中刷题的时候来。 每个练习都写清了它来自哪一节，卡住了就回去看那一节。Practice follows the lessons — every lesson ends with the exercises for that lesson. This page is the whole library, for when you want to drill in one sitting. Each exercise names the lesson it came from, so you can go back when you stall.
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已筛到你正在学的《Federation 考试》。想看全部就点上面的「全部」。Filtered to Federation exam — the course you are on. Use “All” above to see everything.
练习Exercises
筛出 2 个练习（共 148 个）。Showing 2 of 148.来自From 从零重写：空目录到 10 个测试全过Rewrite it: from an empty directory to all 10 tests passing · Federation 考试Federation exam
L4从零重写Rebuild from scratch从零重建 Task 1 · Orders subgraphRebuild Task 1 · the Orders subgraph
空目录开始，搭出一个 Apollo Federation subgraph， 实现四个 resolver 加一个 mutation，让 10 个测试全过， 并且 _service 和 _entities 都能正常工作。不要打开源项目的 orderResolvers.js。
Starting from an empty directory, build an Apollo Federation subgraph. Write four resolvers plus one mutation, get all 10 tests passing, and make both _service and _entities work. Do not open orderResolvers.js from the source project.
需求（不给代码，自己实现）Requirements — no code given, implement it yourself
- 用 @apollo/server + @apollo/subgraph 起一个 subgraph，监听 4000Start a subgraph with @apollo/server + @apollo/subgraph, listening on 4000
- schema 从 .graphql 文件读入，用 buildSubgraphSchema 组装Read the schema from a .graphql file and assemble it with buildSubgraphSchema
- 每个请求构造 context：三个数据源、两个 DataLoader、一个 correlationIdBuild the context per request: three data sources, two DataLoaders, one correlationId
- correlationId 优先取请求头 x-correlation-id，没有就生成Take correlationId from the x-correlation-id request header, and generate one when it is absent
- 实现 User.__resolveReference：把 representation 变成本地对象Write User.__resolveReference: turn the representation into a local object
- 实现 User.orders：按 user.id 取订单，[Order!]! 所以绝不返回 nullWrite User.orders: read orders by user.id; the type is [Order!]!, so never return null
- 实现 Order.shippingInfo：必须走 DataLoader 防 N+1；可空，找不到返回 nullWrite Order.shippingInfo: it must go through the DataLoader to prevent N+1; it is nullable, so return null when nothing is found
- 实现 Query.order：走 DataLoader；找不到抛带 ORDER_NOT_FOUND 的 GraphQLErrorWrite Query.order: go through the DataLoader; when nothing is found, throw a GraphQLError carrying ORDER_NOT_FOUND
- 实现 Query.orders：校验 userId；[Order!]! 所以兜底 []Write Query.orders: validate userId; the type is [Order!]!, so fall back to []
- 实现 Mutation.createOrder：先查商品价格补全 items，再创建；校验失败抛 INVALID_INPUTWrite Mutation.createOrder: look up product prices to complete items first, then create; throw INVALID_INPUT when validation fails
- 两个 DataLoader 的 batch 函数：返回数组的长度与顺序必须和 keys 一一对应The batch function of both DataLoaders: the array it returns must match keys in both length and order
- 所有 resolver 都用 try/catch，catch 第一行放行已有的 GraphQLErrorWrap every resolver in try/catch, and let an existing GraphQLError pass through on the first line of catch
- 所有日志和错误 extensions 里带上 correlationIdCarry correlationId in every log line and in the extensions of every error
你需要自己建的文件Files you create yourself
package.json自己写：type: module、start / test script（test 要带 NODE_OPTIONS=--experimental-vm-modules）、依赖 @apollo/server @apollo/subgraph graphql graphql-tag dataloader，devDep jest @jest/globals，以及内嵌 jest 配置You write it: type: module, the start / test scripts (test needs NODE_OPTIONS=--experimental-vm-modules), the dependencies @apollo/server @apollo/subgraph graphql graphql-tag dataloader, the devDependencies jest @jest/globals, and an inline jest config
src/schema.graphql★ 抄源项目的（这是题目）：User entity + Order/OrderItem/ShippingInfo + enum + Query/Mutation + input★ Copy it from the source project (this is the question): the User entity + Order/OrderItem/ShippingInfo + enum + Query/Mutation + input
src/dataSources/orderDataSource.js★ 抄源项目的（这是题目）：三个 mock 数据源类。注意 OrderDataSource 只有 getOrder / getOrdersByUserId / createOrder★ Copy it from the source project (this is the question): three mock data source classes. Note that OrderDataSource has only getOrder / getOrdersByUserId / createOrder
src/index.js★ 自己写：读 schema、buildSubgraphSchema、ApolloServer + formatError、startStandaloneServer、每请求造 context★ You write it: read the schema, buildSubgraphSchema, ApolloServer + formatError, startStandaloneServer, and build the context per request
src/resolvers/orderResolvers.js★★ 自己写：两个 loader 工厂 + resolvers（User / Order / Query / Mutation）+ ErrorCodes★★ You write it: two loader factories + the resolvers (User / Order / Query / Mutation) + ErrorCodes
__tests__/resolvers.test.js★ 抄源项目的（这是判卷器）：10 个测试，beforeEach 里重建 dataSources 与 loaders★ Copy it from the source project (this is what grades you): 10 tests, with dataSources and loaders rebuilt in beforeEach
verify-schema.mjs★ 自己写：进程内查 _service、普通查询、_entities、mutation★ You write it: query _service in process, then a normal query, then _entities, then the mutation
写完后在本机这样验证Verify it locally like this
npm install
依赖装好，出现 node_modules 与 package-lock.jsonThe dependencies install, and node_modules and package-lock.json appear
npm start
打印 Subgraph ready at http://0.0.0.0:4000/It prints Subgraph ready at http://0.0.0.0:4000/
npm test
Tests: 10 passed, 10 total
node verify-schema.mjs
SDL 出得来且含 @key；orders + shippingInfo 有值；order-999 返回 ORDER_NOT_FOUND；_entities 能拿到 orders；createOrder 的 items[0].price 有值且 totalAmount > 0；空 items 返回 INVALID_INPUTThe SDL comes out and contains @key; orders + shippingInfo have values; order-999 returns ORDER_NOT_FOUND; _entities can read orders; items[0].price from createOrder has a value and totalAmount > 0; empty items returns INVALID_INPUT
提示Hints共 4 级，已看 0 级4 levels, 0 opened
先自己想两分钟。想不出来再点右上角 —— 提示是一级一级放的，不会一次给完。Think for two minutes first. Then use the button above — hints come one level at a time, never all at once.
这一关的意义就在于「没有答案也能写出来」。请确认你已经在本机建好文件、跑过验证命令，再打开参考答案对照。The whole point of this level is writing it with no answer in front of you. Create the files on your machine and run the verification commands first, then come back and compare.
来自From 从零重写：空目录到 10 个测试全过Rewrite it: from an empty directory to all 10 tests passing · Federation 考试Federation exam
L4从零重写Rebuild from scratch从零重建 Task 2 · Spring Boot 控制器Rebuild Task 2 · the Spring Boot controller
给你 OrderService 的方法签名和五个测试。 自己搭一个 Spring Boot 项目，写出六个端点。不要打开源项目的 OrderController.java。
You are given the method signatures of OrderService and five tests. Set up a Spring Boot project yourself and write six endpoints. Do not open OrderController.java from the source project.
需求（不给代码，自己实现）Requirements — no code given, implement it yourself
- Spring Boot 3.3 + Java 17，依赖 web / validation / actuator / testSpring Boot 3.3 + Java 17, with the web / validation / actuator / test dependencies
- 一个 @RestController，构造器注入 OrderServiceOne @RestController, with OrderService injected through the constructor
- GET /api/orders：？userId= 传了就按用户过滤，没传返回全部；200GET /api/orders: filter by user when ?userId= is given, return everything when it is not; 200
- GET /api/orders/{id}：200；找不到时由全局异常处理器给出 404（控制器不要 catch）GET /api/orders/{id}: 200; when nothing is found, the global exception handler answers 404 (do not catch it in the controller)
- GET /api/orders/user/{userId}：200GET /api/orders/user/{userId}: 200
- POST /api/orders：@Valid 校验请求体；成功返回 201 CreatedPOST /api/orders: validate the request body with @Valid; on success return 201 Created
- PATCH /api/orders/{id}/status：body 是 {"status":"..."}；转成 OrderStatus；缺失或非法值返回 400；成功 200PATCH /api/orders/{id}/status: the body is {"status":"..."}; convert it to OrderStatus; a missing or invalid value returns 400; on success 200
- DELETE /api/orders/{id}：204 No ContentDELETE /api/orders/{id}: 204 No Content
- 六个端点都用 SLF4J 打日志，并带上 MDC 里的 correlationIdAll six endpoints log through SLF4J and carry the correlationId from MDC
- 自己写一个 CorrelationIdFilter：读 X-Correlation-ID 头，没有就生成 UUID，放进 MDC，finally 里清理Write your own CorrelationIdFilter: read the X-Correlation-ID header, generate a UUID when it is absent, put it in MDC, and clear it in finally
- 自己写 GlobalExceptionHandler：EntityNotFoundException → 404，MethodArgumentNotValidException → 400Write your own GlobalExceptionHandler: EntityNotFoundException → 404, MethodArgumentNotValidException → 400
你需要自己建的文件Files you create yourself
pom.xmlparent 用 spring-boot-starter-parent 3.3.2，java.version 17，四个依赖 + spring-boot-maven-pluginThe parent is spring-boot-starter-parent 3.3.2, java.version is 17, four dependencies + spring-boot-maven-plugin
src/main/resources/application.propertiesserver.port=8080 就够（顺便按书面题的结论收紧 actuator）server.port=8080 is enough (and tighten actuator while you are here, following the written question)
src/main/java/.../OrderServiceApplication.java@SpringBootApplication + main
src/main/java/.../model/Order.java、OrderItem.java、OrderStatus.java★ 抄源项目的（这是题目）★ Copy it from the source project (this is the question)
src/main/java/.../dto/CreateOrderRequest.java、OrderItemRequest.java★ 抄源项目的：带 @NotBlank / @NotEmpty / @Min / @Valid★ Copy it from the source project: it carries @NotBlank / @NotEmpty / @Min / @Valid
src/main/java/.../repository/OrderRepository.java、InMemoryOrderRepository.java★ 抄源项目的：接口 + 内存实现（含一条种子数据）★ Copy it from the source project: the interface + an in-memory implementation (with one seed record)
src/main/java/.../service/OrderService.java★ 抄源项目的（这是题目）：六个方法，三个会抛 EntityNotFoundException★ Copy it from the source project (this is the question): six methods, three of which throw EntityNotFoundException
src/main/java/.../exception/EntityNotFoundException.java、GlobalExceptionHandler.java★ 自己写：两个 @ExceptionHandler★ You write it: two @ExceptionHandler methods
src/main/java/.../config/CorrelationIdFilter.java★ 自己写：OncePerRequestFilter + MDC★ You write it: OncePerRequestFilter + MDC
src/main/java/.../controller/OrderController.java★★ 自己写：六个端点★★ You write it: six endpoints
src/test/java/.../OrderControllerTest.java★ 抄源项目的（这是判卷器）：@WebMvcTest + @MockBean + 五个测试★ Copy it from the source project (this is what grades you): @WebMvcTest + @MockBean + five tests
写完后在本机这样验证Verify it locally like this
mvn test
Tests run: 5, Failures: 0, Errors: 0 — BUILD SUCCESS
mvn spring-boot:run
服务起在 8080，日志里能看到 Started OrderServiceApplicationThe service starts on 8080, and the log shows Started OrderServiceApplication
curl -i -s localhost:8080/api/orders/999
404 + {"timestamp":...,"status":404,"message":"Order not found with id: 999"}
curl -i -s -X POST localhost:8080/api/orders -H 'Content-Type: application/json' -d '{"userId":"123","items":[{"productId":"prod-789","quantity":2}]}'
201 Created + 订单 JSON（totalAmount 应为 299.98）201 Created + the order JSON (totalAmount should be 299.98)
curl -i -s -X POST localhost:8080/api/orders -H 'Content-Type: application/json' -d '{"userId":"","items":[]}'
400 Bad Request（Bean Validation 生效）400 Bad Request (Bean Validation is working)
curl -i -s -X PATCH localhost:8080/api/orders/1/status -H 'Content-Type: application/json' -d '{"status":"FLYING"}'
400 Bad Request（不是 500）400 Bad Request (not 500)
curl -i -s -X DELETE localhost:8080/api/orders/1
204 No Content，body 为空204 No Content, with an empty body
curl -i -s -H 'X-Correlation-ID: my-trace-1' localhost:8080/api/orders
响应头里有同一个 X-Correlation-ID；服务端日志里也是它The response header carries the same X-Correlation-ID, and so does the server log
提示Hints共 4 级，已看 0 级4 levels, 0 opened
先自己想两分钟。想不出来再点右上角 —— 提示是一级一级放的，不会一次给完。Think for two minutes first. Then use the button above — hints come one level at a time, never all at once.
这一关的意义就在于「没有答案也能写出来」。请确认你已经在本机建好文件、跑过验证命令，再打开参考答案对照。The whole point of this level is writing it with no answer in front of you. Create the files on your machine and run the verification commands first, then come back and compare.