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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练习Exercises
筛出 9 个练习（共 148 个）。Showing 9 of 148.来自From TODO 1 · User.ordersTODO 1 · User.orders · Federation 考试Federation exam
L3写整块Write a block不看答案，自己写出 User.ordersWrite User.orders yourself, without looking at the answer
按 TODO 的三条要求写完整实现。检查器会核对方法名、兜底、 错误处理和 correlation id。
Write the full implementation against the three requirements in the TODO. The checker looks at the method name, the fallback, the error handling and the correlation id.
要求Requirements
- 用 user.id 去取该用户的订单Use user.id to fetch that user's orders
- 调用数据源上真实存在的方法Call a method that really exists on the data source
- 绝不返回 null 或 undefined（schema 是 [Order!]!）Never return null or undefined (the schema says [Order!]!)
- 用 try/catch 包住，失败时抛 GraphQLErrorWrap it in try/catch and throw a GraphQLError on failure
- 错误的 extensions 里带 code 和 correlationIdPut code and correlationId in the error's extensions
- 已经是 GraphQLError 的错误要原样往上抛，不要重新包装Rethrow an error that is already a GraphQLError untouched, without rewrapping it
- 日志里带上 correlationIdInclude correlationId in the log line
This check is textual: it looks for the right constructs, it does not run your code
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.
看答案之前，先确认你已经自己动手写过一遍。看懂别人的答案和自己写出来，是两种能力。Before you open this, make sure you have written it yourself once. Following someone else's answer and producing your own are two different skills.
来自From TODO 3 & 4 · Query.order 与 Query.ordersTODO 3 & 4 · Query.order and Query.orders · Federation 考试Federation exam
L3写整块Write a block不看答案，自己写出两个 Query resolverWrite both Query resolvers yourself, without looking at the answer
两个函数一起写。注意它们的数据来源、兜底策略、 context 解构都不一样。
Write both functions together. They differ in where they read from, what they fall back to, and what they destructure out of context.
要求Requirements
- Query.order 用 orderLoader 取数据Query.order reads through orderLoader
- Query.order 找不到时抛带 ORDER_NOT_FOUND code 的 GraphQLErrorWhen Query.order finds nothing, it throws a GraphQLError carrying the ORDER_NOT_FOUND code
- Query.orders 用 orderDataSource.getOrdersByUserId 取数据Query.orders reads through orderDataSource.getOrdersByUserId
- Query.orders 校验 userId，非法时抛 INVALID_INPUTQuery.orders validates userId and throws INVALID_INPUT when it is not valid
- Query.orders 绝不返回 null（schema 是 [Order!]!）Query.orders never returns null (the schema says [Order!]!)
- 两个都用 try/catch，catch 里先放行已有的 GraphQLErrorBoth use try/catch, and the catch lets an existing GraphQLError through first
- 两个都在日志里带上 correlationIdBoth include correlationId in their log line
This check is textual: it looks for the right constructs, it does not run your code
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.
看答案之前，先确认你已经自己动手写过一遍。看懂别人的答案和自己写出来，是两种能力。Before you open this, make sure you have written it yourself once. Following someone else's answer and producing your own are two different skills.
来自From 三处埋雷：怎么系统地找出来The three planted bugs: how to find them systematically · Federation 考试Federation exam
L3Debug LabDebug LabDebug Lab · Cannot read properties of undefinedDebug Lab · Cannot read properties of undefined
Mutation.createOrder 的测试挂了。 报错说在读一个 undefined 的属性。自己分诊。
The Mutation.createOrder test fails. The error says something read a property of undefined. Diagnose it yourself.
● Order Resolvers › Mutation.createOrder resolver › should create a new order successfully
GraphQLError: Failed to create order
91 | } catch (error) {
92 | console.error(`[${correlationId}] Error creating order:`, error.message);
> 93 | throw new GraphQLError('Failed to create order', {
# 往上翻，console.error 打出的原始错误是：
console.error
[test-correlation-id] Error creating order: Cannot read properties of
undefined (reading 'createOrder')● Order Resolvers › Mutation.createOrder resolver › should create a new order successfully
GraphQLError: Failed to create order
91 | } catch (error) {
92 | console.error(`[${correlationId}] Error creating order:`, error.message);
> 93 | throw new GraphQLError('Failed to create order', {
# Scroll up: the raw error that console.error printed is
console.error
[test-correlation-id] Error creating order: Cannot read properties of
undefined (reading 'createOrder')
1const order = await dataSources.orderAPI.createOrder({ userId, items });
2
3// 参考：index.js 里 context 的 return
4// return {
5// dataSources: { orderDataSource, inventoryDataSource, shippingDataSource },
6// loaders: { shippingInfoLoader, orderLoader },
7// correlationId
8// };
1const order = await dataSources.orderAPI.createOrder({ userId, items });
2
3// For reference: what the context function in index.js returns
4// return {
5// dataSources: { orderDataSource, inventoryDataSource, shippingDataSource },
6// loaders: { shippingInfoLoader, orderLoader },
7// correlationId
8// };
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 三处埋雷：怎么系统地找出来The three planted bugs: how to find them systematically · Federation 考试Federation exam
L3Debug LabDebug LabDebug Lab · 错误码不对（不报错的那种 bug）Debug Lab · The wrong error code (the kind of bug that throws nothing)
代码跑得通，没有异常。但测试说错误码不对。 这是三处埋雷里最值得理解的一处。
The code runs and raises no exception, but the test says the error code is wrong. Of the three planted bugs, this is the one most worth understanding.
● Order Resolvers › Error handling › should return structured error for validation failures
expect(received).toBe(expected) // Object.is equality
Expected: "INVALID_INPUT"
Received: "SERVICE_ERROR"
# 测试代码：
# const input = { userId: '789', items: [] }; ← 空 items，应该被校验拦下
# try {
# await resolvers.Mutation.createOrder({}, input, context);
# throw new Error('Should have thrown an error');
# } catch (error) {
# expect(error.extensions.code).toBe('INVALID_INPUT');
# }● Order Resolvers › Error handling › should return structured error for validation failures
expect(received).toBe(expected) // Object.is equality
Expected: "INVALID_INPUT"
Received: "SERVICE_ERROR"
# The test code:
# const input = { userId: '789', items: [] }; ← empty items, validation should stop it
# try {
# await resolvers.Mutation.createOrder({}, input, context);
# throw new Error('Should have thrown an error');
# } catch (error) {
# expect(error.extensions.code).toBe('INVALID_INPUT');
# }
1try {
2 if (!userId || !items || items.length === 0) {
3 throw new GraphQLError('Invalid order input', {
4 extensions: { code: ErrorCodes.INVALID_INPUT, correlationId }
5 });
6 }
7 const order = await dataSources.orderDataSource.createOrder(userId, pricedItems);
8 return order;
9} catch (error) {
10 console.error(`[${correlationId}] Error creating order:`, error.message);
11 throw new GraphQLError('Failed to create order', {
12 extensions: { code: ErrorCodes.SERVICE_ERROR, correlationId }
13 });
14}
1try {
2 if (!userId || !items || items.length === 0) {
3 throw new GraphQLError('Invalid order input', {
4 extensions: { code: ErrorCodes.INVALID_INPUT, correlationId }
5 });
6 }
7 const order = await dataSources.orderDataSource.createOrder(userId, pricedItems);
8 return order;
9} catch (error) {
10 console.error(`[${correlationId}] Error creating order:`, error.message);
11 throw new GraphQLError('Failed to create order', {
12 extensions: { code: ErrorCodes.SERVICE_ERROR, correlationId }
13 });
14}
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 六个端点：状态码就是这道题的全部Six endpoints: the status codes are the whole task · Federation 考试Federation exam
L3写整块Write a block不看答案，自己写出全部六个端点Write all six endpoints yourself, without looking at the answer
六个端点一起写。业务逻辑全部调 orderService， 你负责选对状态码、处理可选参数、转 enum、打日志。
Write all six endpoints. Every piece of business logic goes through orderService; your job is picking the right status codes, handling the optional parameter, converting the enum, and logging.
要求Requirements
- 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, otherwise return everything; 200
- GET /api/orders/{id}：200；不要 try/catch，让 404 由全局处理器给出GET /api/orders/{id}: 200; no try/catch, let the global handler produce the 404
- GET /api/orders/user/{userId}：200GET /api/orders/user/{userId}: 200
- POST /api/orders：201 CreatedPOST /api/orders: 201 Created
- PATCH /api/orders/{id}/status：把 body 里的字符串转成 OrderStatus；缺失或非法值返回 400；成功 200PATCH /api/orders/{id}/status: convert the string in the body into an OrderStatus; return 400 when it is missing or invalid; 200 on success
- DELETE /api/orders/{id}：204 No ContentDELETE /api/orders/{id}: 204 No Content
- 六个端点都用 logger.info 打日志，并带上 MDC 里的 correlationIdAll six endpoints log with logger.info and include the correlationId from the MDC
This check is textual: it looks for the right constructs, it does not run your code
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.
看答案之前，先确认你已经自己动手写过一遍。看懂别人的答案和自己写出来，是两种能力。Before you open this, make sure you have written it yourself once. Following someone else's answer and producing your own are two different skills.
来自From 六个端点：状态码就是这道题的全部Six endpoints: the status codes are the whole task · Federation 考试Federation exam
L3Debug LabDebug LabDebug Lab · 查一个不存在的订单，返回了 200Debug Lab · Asking for an order that does not exist returns 200
五个测试全过。但手动 curl 一个不存在的 id， 得到 200 和一个空 body。期望是 404 加一段 JSON。
All five tests pass. But curl an id that does not exist by hand and you get a 200 with an empty body. It should be a 404 with a piece of JSON.
$ curl -i -s localhost:8080/api/orders/999
HTTP/1.1 200
Content-Length: 0
# 期望：
# HTTP/1.1 404
# { "timestamp": "...", "status": 404, "message": "Order not found with id: 999" }
# mvn test：Tests run: 5, Failures: 0 ← 测试全过！$ curl -i -s localhost:8080/api/orders/999
HTTP/1.1 200
Content-Length: 0
# Expected:
# HTTP/1.1 404
# { "timestamp": "...", "status": 404, "message": "Order not found with id: 999" }
# mvn test: Tests run: 5, Failures: 0 ← every test passes!
1@GetMapping("/api/orders/{id}")
2public ResponseEntity<Order> getOrderById(@PathVariable Long id) {
3 logger.info("GET /api/orders/{} correlationId={}", id, correlationId());
4 try {
5 return ResponseEntity.ok(orderService.getOrderById(id));
6 } catch (EntityNotFoundException ex) {
7 return null;
8 }
9}
1@GetMapping("/api/orders/{id}")
2public ResponseEntity<Order> getOrderById(@PathVariable Long id) {
3 logger.info("GET /api/orders/{} correlationId={}", id, correlationId());
4 try {
5 return ResponseEntity.ok(orderService.getOrderById(id));
6 } catch (EntityNotFoundException ex) {
7 return null;
8 }
9}
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 两道书面题：延迟传播与生产配置The two written questions: how delay spreads, and production configuration · Federation 考试Federation exam
L3写整块Write a block写出 actuator 那一条的修正配置Write the corrected configuration for the actuator lineDrillLab 自出Written by DrillLab
针对 management.endpoints.web.exposure.include=*， 写出修正后的配置。至少要做到：白名单、管理端口分离、 health 不泄漏细节、支持 k8s 探针。
Write the corrected configuration for management.endpoints.web.exposure.include=*. At a minimum: an allow list, management on its own port, a health endpoint that leaks no detail, and support for Kubernetes probes.
要求Requirements
- 用白名单列出需要的端点，不用 *List the endpoints you need in an allow list; do not use *
- management.server.port 设成与业务端口不同的值Set management.server.port to something other than the business port
- health 端点不显示详情The health endpoint shows no details
- 开启 health probes（liveness / readiness）Turn on the health probes (liveness and readiness)
This check is textual: it looks for the right constructs, it does not run your code
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.
看答案之前，先确认你已经自己动手写过一遍。看懂别人的答案和自己写出来，是两种能力。Before you open this, make sure you have written it yourself once. Following someone else's answer and producing your own are two different skills.
来自From Debug Lab · Federation 十种典型故障Debug Lab · ten common Federation failures · Federation 考试Federation exam
L3Debug LabDebug Lab故障 1 · resolver 写了，字段还是 nullFault 1 · the resolver is written, the field is still null
你确信写了 shippingInfo 的实现， 测试也不报错，但查询返回的 shippingInfo 是null。控制台里连你加的 log 都没打印。
You are sure you wrote an implementation for shippingInfo, and no test reports anything, but the query returns shippingInfo as null. Not even the log line you added prints on the console.
# 没有任何报错。
$ node verify-schema.mjs
Query.orders + shippingInfo: {"orders":[
{"id":"order-456","status":"SHIPPED","shippingInfo":null},
{"id":"order-457","status":"DELIVERED","shippingInfo":null}]}
errors: []
# 你在 resolver 第一行加的 console.log('>>> shippingInfo called')
# 一次都没打印。# No error at all.
$ node verify-schema.mjs
Query.orders + shippingInfo: {"orders":[
{"id":"order-456","status":"SHIPPED","shippingInfo":null},
{"id":"order-457","status":"DELIVERED","shippingInfo":null}]}
errors: []
# The console.log('>>> shippingInfo called') you added as the resolver's first line
# never printed, not once.
1export const resolvers = {
2 Order: {
3 async shipping(parent, _, { loaders }) { // ← 名字
4 console.log('>>> shippingInfo called');
5 return loaders.shippingInfoLoader.load(parent.id);
6 }
7 },
8 ...
9};
10
11// 参考 schema.graphql：
12// type Order {
13// ...
14// shippingInfo: ShippingInfo
15// }
1export const resolvers = {
2 Order: {
3 async shipping(parent, _, { loaders }) { // ← the name
4 console.log('>>> shippingInfo called');
5 return loaders.shippingInfoLoader.load(parent.id);
6 }
7 },
8 ...
9};
10
11// For reference, schema.graphql says:
12// type Order {
13// ...
14// shippingInfo: ShippingInfo
15// }
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From Debug Lab · Federation 十种典型故障Debug Lab · ten common Federation failures · Federation 考试Federation exam
L3Debug LabDebug Lab故障 3 · A 拿到了 B 的数据Fault 3 · A receives B's data
查两个订单的物流，返回的数据对上了错的订单。 没有任何报错。这是 DataLoader 最阴险的一类误用。
You query the shipping info for two orders and the data comes back attached to the wrong order. Nothing reports an error. This is the hardest kind of DataLoader misuse to notice.
# 没有任何报错。
# 查询：{ orders(userId:"123") { id shippingInfo { trackingNumber } } }
#
# 期望：
# order-456 -> TRACK123456
# order-457 -> TRACK123457
#
# 实际：
# order-456 -> TRACK123457 ← 串了！
# order-457 -> null
# 日志：[DataLoader] Batching 2 shipping info requests ← 合并是生效的# No error at all.
# Query: { orders(userId:"123") { id shippingInfo { trackingNumber } } }
#
# Expected:
# order-456 -> TRACK123456
# order-457 -> TRACK123457
#
# Actual:
# order-456 -> TRACK123457 ← got the other one's number!
# order-457 -> null
# Log: [DataLoader] Batching 2 shipping info requests ← the batching does work
1function createShippingInfoLoader(shippingDataSource) {
2 return new DataLoader(async orderIds => {
3 console.log(`[DataLoader] Batching ${orderIds.length} shipping info requests`);
4
5 const all = await Promise.all(
6 orderIds.map(id => shippingDataSource.getShippingInfo(id))
7 );
8
9 // 「过滤掉没有物流信息的」—— 看起来很合理
10 return all.filter(info => info !== null);
11 });
12}
1function createShippingInfoLoader(shippingDataSource) {
2 return new DataLoader(async orderIds => {
3 console.log(`[DataLoader] Batching ${orderIds.length} shipping info requests`);
4
5 const all = await Promise.all(
6 orderIds.map(id => shippingDataSource.getShippingInfo(id))
7 );
8
9 // "drop the ones with no shipping info" — this looks reasonable
10 return all.filter(info => info !== null);
11 });
12}
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this