我有一个 serde_json::Value我希望它包含一个对象数组。我想从这些对象中提取 2 个值并在任何失败时返回错误。到目前为止，这是我的代码:
use std::collections::HashMap;
use anyhow::Result;
fn get_stock(response: serde_json::Value) -> Result<HashMap<String, u32>>{
response["products"]
.as_array()?.iter()
.map(|product| {
let product = product.as_object()?;
(
product["name"].as_str()?.to_owned(),
//as_u64 fails for some reason
product["stock"].as_str()?.parse::<u32>()?,
)
})
.collect()?
}
当我使用 .unwrap() 时这工作正常，但在将返回类型更改为 Result 之后并用 ? 替换 unwraps我收到以下编译错误:
error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
--> src/bin/products.rs:7:20
|
5 | / fn get_stock(response: serde_json::Value) -> Result<HashMap<String, u32>>{
6 | | response["products"]
7 | | .as_array()?.iter()
| | ^ use `.ok_or(...)?` to provide an error compatible with `Result<HashMap<std::string::String, u32>, anyhow::Error>`
8 | | .map(|product| {
... |
16 | | .collect()?
17 | | }
| |_- this function returns a `Result`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<HashMap<std::string::String, u32>, anyhow::Error>`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:9:46
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
10 | | (
11 | | product["name"].as_str()?.to_owned(),
... |
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:11:41
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
... |
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:13:42
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
12 | | //as_u64 fails for some reason
13 | | product["stock"].as_str()?.parse::<u32>()?,
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:13:58
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
12 | | //as_u64 fails for some reason
13 | | product["stock"].as_str()?.parse::<u32>()?,
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
miav@battlestation catbot % cargo run --bin products
Compiling catbot v0.1.0 (/Users/miav/Documents/Personal/Projects/programming/catbot)
error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
--> src/bin/products.rs:7:20
|
5 | / fn get_stock(response: serde_json::Value) -> Result<HashMap<String, u32>>{
6 | | response["products"]
7 | | .as_array()?.iter()
| | ^ use `.ok_or(...)?` to provide an error compatible with `Result<HashMap<std::string::String, u32>, anyhow::Error>`
8 | | .map(|product| {
... |
16 | | .collect()?
17 | | }
| |_- this function returns a `Result`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<HashMap<std::string::String, u32>, anyhow::Error>`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:9:46
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
10 | | (
11 | | product["name"].as_str()?.to_owned(),
... |
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:11:41
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
... |
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:13:42
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
12 | | //as_u64 fails for some reason
13 | | product["stock"].as_str()?.parse::<u32>()?,
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Option<Infallible>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
--> src/bin/products.rs:13:58
|
8 | .map(|product| {
| ______________-
9 | | let product = product.as_object()?;
10 | | (
11 | | product["name"].as_str()?.to_owned(),
12 | | //as_u64 fails for some reason
13 | | product["stock"].as_str()?.parse::<u32>()?,
| | ^ cannot use the `?` operator in a closure that returns `(std::string::String, u32)`
14 | | )
15 | | })
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `FromResidual<Result<Infallible, ParseIntError>>` is not implemented for `(std::string::String, u32)`
= note: required by `from_residual`
error: aborting due to 5 previous errors
我事先不知道JSON的确切结构，所以无法将其解析成结构体。我所知道的是，它很可能是一组具有 name 的对象。字符串字段和一个 stock整数字段，我想将其提取到 map 中。如果情况并非如此，那么我想返回一个错误。最简单的方法是什么？
更新: 在遵循 Lagerbaer 的建议并进行一些挖掘之后，我想出了以下解决方案。
use anyhow::{anyhow, Result};
use std::collections::HashMap;
fn get_stock(response: serde_json::Value) -> Result<HashMap<String, u32>> {
response
.get("products")
.ok_or(anyhow!("'products' not found"))?
.as_array()
.ok_or(anyhow!("'products' is not an array"))?
.iter()
.map(|product| -> Result<(String, u32)> {
let product = product.as_object().unwrap();
Ok((
product
.get("name")
.ok_or(anyhow!("'name' not found"))?
.as_str()
.ok_or(anyhow!("'name' is not a string"))?
.trim()
.to_owned(),
//as_u64 fails for some reason
product
.get("stock")
.ok_or(anyhow!("'stock' not found"))?
.as_str()
.ok_or(anyhow!("'stock' is not a string"))?
.parse::<u32>()?,
))
})
.collect()
}
二手 ok_or()到 map Option至 Result , 必须使用 anyhow!宏以使其与 anyhow 结果类型兼容。
事实证明 collect()实际上接受一个迭代器
Result<(String, u32)>产生一个Result<HashMap<String, u32>>具有我想要的确切行为，即返回第一个错误或完整的 HashMap (如果没有错误)。
最佳答案
所以这里有几个问题，编译器会尽力告诉你。
我会先引导您开始，然后我鼓励您尝试单独进行一段时间。
所以第一个错误显然是，as_array 返回一个 Option 而不是 Result，因此，您不能使用? 运算符。
幸运的是，编译器会告诉您该怎么做:Option 有一个您应该调用的方法ok_or。它会将 Option 转换为 Result。如果 Option 是 Some(value) 你会得到一个 Ok(value)，如果 Option是 None，您将得到您在 ok_or 参数中指定的任何错误。
另一个容易发现的错误是:您的函数返回一个 Result，因此返回值显然应该是一个 Result。因此最后一个 ? 应该被删除，因为那个 ? 会接受一个 Result 并将它变成“纯”值(如果结果是 Ok)。
然后剩下的就是弄清楚闭包应该返回什么。也许您可以在修正我上面解释的其他错误后尝试这样做。
关于json - 从 serde_json 中的非类型化 JSON 中提取数据时如何处理错误？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/69057008/