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.
练习Exercises
筛出 50 个练习（共 148 个） · 第 3 / 5 页。Showing 50 of 148 · page 3 / 5.schema 写的是 orders(userId: ID!): [Order!]!。 user 999 没有任何订单。resolver 该返回什么？
The schema says orders(userId: ID!): [Order!]!. User 999 has no orders at all. What should the resolver return?
客户端调 createOrder(userId: "789", items: [{ productId: "prod-789", quantity: 2 }])。 如果 resolver 把 items 原样交给orderDataSource.createOrder，会怎样？
The client calls createOrder(userId: "789", items: [{ productId: "prod-789", quantity: 2 }]). What happens if the resolver hands items straight to orderDataSource.createOrder?
下面哪一条最准确地描述了 Federation 要解决的核心问题？
Which of these describes most accurately the core problem Federation sets out to solve?
下面哪些是这个 assessment 仓库里没有的？（多选）
Which of these are not in this exam repository? (Select all that apply.)
这题是多选。More than one answer is correct.
schema.graphql 里从头到尾没有出现_entities，但 Router 能查它。它从哪来？
_entities appears nowhere in schema.graphql, yet the Router can query it. Where does it come from?
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?
type User @key(fields: "id") 最准确的含义是？
What does type User @key(fields: "id") mean, most precisely?
__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, ...)?
下面哪一条最准确？
Which of these is most accurate?
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?
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?
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?