DrillLab
开始StartNode.js, npm, node_modules and the lockfile
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.

0 / 148个做对过you got right
筛一下Filter theseFederation 考试Federation exam
课程Course全部All地基 · 项目与语言Foundations · project and languageReact 考试React examFederation 考试Federation exam面试八股Interview questionsCab BookingCab Booking
难度LevelL1 → L4 和上面四档同一个意思：给你的东西越来越少L1 → L4: the same idea as the four tiers above — less is handed to you全部难度All levelsL1L1L2L2L3L3L4L4
类型Kind全部类型All kinds认出来Spot it排顺序Order it填空Fill the blanks写整块Write a blockDebug LabDebug Lab从零重写Rebuild from scratch

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 47 个练习（共 148 个） · 第 2 / 4 页。Showing 47 of 148 · page 2 / 4.
来自From subgraph 是怎么跑起来的How a subgraph starts up · Federation 考试Federation exam
L1认出来Spot it本地怎么验证 federation 部分How to check the Federation part locally

仓库里没有 Router。你想确认自己的 User.orders在 federation 链路里能被正确调用。最直接的办法？

There is no Router in the repository. You want to confirm your User.orders is called correctly along the federation path. What is the most direct way?

先选一个选项Pick an option first
来自From entity、@key 与 __resolveReferenceentity, @key and __resolveReference · Federation 考试Federation exam
L1认出来Spot it@key 在声明什么What @key declares

type User @key(fields: "id") 最准确的含义是？

What does type User @key(fields: "id") mean, most precisely?

先选一个选项Pick an option first
来自From entity、@key 与 __resolveReferenceentity, @key and __resolveReference · Federation 考试Federation exam
L1认出来Spot itUser.orders 里的 user 参数上有什么What the user argument of User.orders carries

__resolveReference 返回 { id: user.id }。 那么 User.orders(user, ...) 里的 user上有哪些属性？

__resolveReference returns { id: user.id }. So which properties does user have inside User.orders(user, ...)?

先选一个选项Pick an option first
来自From entity、@key 与 __resolveReferenceentity, @key and __resolveReference · Federation 考试Federation exam
L2填空Fill the blanks补全 entity 声明与引用解析Fill in the entity declaration and the reference resolver

三个空。第一个是 directive，第二个是标记「这不是我的字段」， 第三个是引用解析要返回什么。

Three blanks. The first is a directive, the second marks a field as not belonging to this service, and the third is what the reference resolver returns.

GRAPHQLschema.graphql + orderResolvers.js3 个空3 blanks
1# schema.graphql
2type User (fields: "id") {
3 id: ID!
4 orders: [Order!]!
5}
6
7# orderResolvers.js
8# User: {
9# __resolveReference(user, { dataSources, loaders }) {
10# return { id: };
11# },
12# ...
13# }
把 3 个空都填上才能检查（还差 3 个）Fill all 3 blanks to check (3 to go)
来自From N+1 问题与 DataLoaderThe N+1 problem and DataLoader · Federation 考试Federation exam
L1认出来Spot itDataLoader 靠什么把 N 次合并成 1 次How DataLoader turns N calls into 1

下面哪一条最准确？

Which of these is most accurate?

先选一个选项Pick an option first
来自From N+1 问题与 DataLoaderThe N+1 problem and DataLoader · Federation 考试Federation exam
L1认出来Spot itbatch 函数里哪种写法是错的Which return value from a batch function is wrong

batch 函数收到 ids = ['a', 'b', 'c']， 其中 b 在数据库里不存在。下面哪种返回是错的?

The batch function receives ids = ['a', 'b', 'c'], and b does not exist in the database. Which of these return values is wrong?

先选一个选项Pick an option first
来自From N+1 问题与 DataLoaderThe N+1 problem and DataLoader · Federation 考试Federation exam
L2填空Fill the blanks修好 createOrderLoader 并写出 shippingInfoFix createOrderLoader and write shippingInfo

两个空。第一个要你填对数据源上真实存在的方法名， 第二个要你用 loader 而不是数据源。

Two blanks. The first wants the name of a method that really exists on the data source; the second wants you to go through the loader rather than the data source.

JSsrc/resolvers/orderResolvers.js2 个空2 blanks
1function createOrderLoader(orderDataSource) {
2 return new DataLoader(async orderIds => {
3 const orders = await Promise.all(
4 orderIds.map(id => orderDataSource.(id))
5 );
6 return orders;
7 });
8}
9
10// Order.shippingInfo —— 必须走 loader，否则 N+1 考点没答到
11async shippingInfo(parent, _, { dataSources, loaders, correlationId }) {
12 const shippingInfo = await loaders..load(parent.id);
13 return shippingInfo ?? null;
14}
把 2 个空都填上才能检查（还差 2 个）Fill all 2 blanks to check (2 to go)
来自From N+1 问题与 DataLoaderThe N+1 problem and DataLoader · Federation 考试Federation exam
L2Debug LabDebug LabDebug Lab · DataLoader 报 is not a functionDebug Lab · DataLoader reports is not a function

跑 npm test，其中一个 DataLoader 相关的测试挂了。 报错指向 loader 内部。

You run npm test and one of the DataLoader tests fails. The error points inside the loader.

第 1 步 · 先看现象和代码，别急着改Step 1 · read the symptom and the code before you touch anything
● Order Resolvers › DataLoader functionality › should batch multiple order requests TypeError: orderDataSource.getOrderById is not a function 29 | 30 | const orders = await Promise.all( > 31 | orderIds.map(id => orderDataSource.getOrderById(id)) | ^ 32 | ); 33 | 34 | return orders; at src/resolvers/orderResolvers.js:31:42 at Array.map (<anonymous>) at DataLoader._batchLoadFn (src/resolvers/orderResolvers.js:31:16)
JavaScriptsrc/resolvers/orderResolvers.js示意Illustrative
1function createOrderLoader(orderDataSource) {
2 return new DataLoader(async orderIds => {
3 const orders = await Promise.all(
4 orderIds.map(id => orderDataSource.getOrderById(id))
5 );
6 return orders;
7 });
8}
9
10// 参考：OrderDataSource 上真实存在的方法
11// class OrderDataSource {
12// async getOrder(id) { ... }
13// async getOrdersByUserId(userId) { ... }
14// async createOrder(userId, items) { ... }
15// }
1function createOrderLoader(orderDataSource) {
2 return new DataLoader(async orderIds => {
3 const orders = await Promise.all(
4 orderIds.map(id => orderDataSource.getOrderById(id))
5 );
6 return orders;
7 });
8}
9
10// For reference: the methods OrderDataSource really has
11// class OrderDataSource {
12// async getOrder(id) { ... }
13// async getOrdersByUserId(userId) { ... }
14// async createOrder(userId, items) { ... }
15// }
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 先读题：四个 TODO、三处埋雷、十个测试Read the task first: four TODOs, three planted bugs, ten tests · Federation 考试Federation exam
L1认出来Spot it为什么基线里有 4 个测试是通过的Why 4 tests already pass at the baseline

四个 TODO 全都只写了 return [] 或return null，为什么还有 4 个测试通过？

All four TODOs contain nothing but return [] or return null. So why do 4 tests still pass?

先选一个选项Pick an option first
来自From 先读题：四个 TODO、三处埋雷、十个测试Read the task first: four TODOs, three planted bugs, ten tests · Federation 考试Federation exam
L1认出来Spot it埋雷 1 该在哪个文件修Which file should planted bug 1 be fixed in

createOrderLoader 调了不存在的orderDataSource.getOrderById(id)。 正确的修法是？

createOrderLoader calls orderDataSource.getOrderById(id), which does not exist. What is the right fix?

先选一个选项Pick an option first
来自From 先读题：四个 TODO、三处埋雷、十个测试Read the task first: four TODOs, three planted bugs, ten tests · Federation 考试Federation exam
L1排顺序Order it把 Task 1 的推进顺序排对Put the steps of Task 1 in the right order

拿到 node-subgraph，最合理的动作顺序？

You have just opened node-subgraph. What is the most sensible order to work in?

1逐个实现四个 TODOImplement the four TODOs one by one
2读 schema.graphql，记下四个返回类型的可空性Read schema.graphql and note the nullability of the four return types
3npm install，然后 npm test 拿到 6 failed / 4 passed 的基线npm install, then npm test to get the 6 failed / 4 passed baseline
4npm test 转绿，再写个 verify 脚本查 _service 和 _entitiesOnce npm test is green, write a verify script that checks _service and _entities
5读 index.js 和 dataSources，抄下 context 键名与方法名Read index.js and the dataSources, and copy out the context keys and method names
6修三处埋雷Fix the three planted bugs
来自From TODO 1 · User.ordersTODO 1 · User.orders · Federation 考试Federation exam
L2填空Fill the blanks补全 User.ordersFill in User.orders

四个空。第 2 个是数据源上的真实方法名， 第 4 个是那行最容易漏的防御。

Four blanks. The second is the method name that really exists on the data source; the fourth is the guard people most often forget.

JSsrc/resolvers/orderResolvers.js4 个空4 blanks
1async orders(user, _, { dataSources, loaders, correlationId }) {
2 try {
3 console.log(`[${correlationId}] Resolving User.orders for userId: ${user.}`);
4
5 const orders = await dataSources.orderDataSource.(user.id);
6
7 return orders [];
8 } catch (error) {
9 if (error GraphQLError) throw error;
10
11 console.error(`[${correlationId}] Error:`, error.message);
12 throw new GraphQLError('Failed to fetch orders for user', {
13 extensions: { code: ErrorCodes.SERVICE_ERROR, correlationId }
14 });
15 }
16}
把 4 个空都填上才能检查（还差 4 个）Fill all 4 blanks to check (4 to go)