[英]Why is a trait not implemented for a type that clearly has it implemented?
I'm trying to use Diesel to query a MySQL database and display the results with a Handlebars template with Rocket .我正在尝试使用Diesel查询 MySQL 数据库并使用带有Rocket的 Handlebars 模板显示结果。
I have this in models.rs我在models.rs中有这个
#[derive(Queryable, Serialize)]
pub struct Post {
pub id: i32,
pub title: String,
pub text: String,
pub published: bool,
}
cargo run
outputs this: cargo run
输出:
--> src/main.rs:69:5
|
69 | Template::render("index", &results)
| ^^^^^^^^^^^^^^^^ the trait `serde::ser::Serialize` is not implemented for `tasty::models::Post`
|
= note: required because of the requirements on the impl of `serde::ser::Serialize` for `std::vec::Vec<tasty::models::Post>`
= note: required by `rocket_contrib::Template::render`
In my Cargo.toml, I have this:在我的 Cargo.toml 中,我有这个:
[dependencies]
chrono = "0.3.0"
rocket = "0.2.8"
rocket_codegen = "0.2.8"
serde = "1.0.8"
serde_derive = "1.0.8"
serde_json = "1.0.2"
mysql = "11.1.2"
diesel = { version = "0.13.0", features = ["mysql","chrono"] }
diesel_codegen = { version = "0.13.0", features = ["mysql"] }
dotenv = "0.10.0"
[dependencies.rocket_contrib]
version = "*"
default-features = false
features = ["handlebars_templates"]
I have read that Diesel does not support Serialize
at the moment, but I am not sure.我读过 Diesel 目前不支持
Serialize
,但我不确定。
The general problem is that the code has multiple versions of the crate, each providing a different version of the traits.一般的问题是代码有多个版本的板条箱,每个版本都提供不同版本的特征。 The fact that Rust allows this is a good thing , but the error messages around it are confusing .
Rust 允许这样做是一件好事,但它周围的错误消息令人困惑。
Your crate implements Serialize
from version A but the library is using version B in a public interface .您的板条箱从版本 A 实现
Serialize
,但该库在公共接口中使用版本 B。 These traits are not compatible, so when you pass your type implementing Serialize@A
to the function requiring Serialize@B
, the compiler stops you.这些特征不兼容,因此当您将实现
Serialize@A
的类型传递给需要Serialize@B
的函数时,编译器会阻止您。
While your example is about different traits, it's also possible for this to occur for types which have been re-exported from a crate.虽然您的示例是关于不同特征的,但对于从板条箱重新导出的类型也可能发生这种情况。
cargo tree
, available starting in Rust 1.44 is highly useful to verify this is your problem.从Rust 1.44开始提供的
cargo tree
对验证这是您的问题非常有用。 It shows all of your dependencies and their versions.它显示了您的所有依赖项及其版本。 It even has a
-d
flag to show duplicate dependencies!它甚至有一个
-d
标志来显示重复的依赖关系! That mode isn't shown here, but is highly useful.该模式未在此处显示,但非常有用。
The general solution is to manually restrict your version of Serde in your Cargo.toml to match the rest of the dependencies:一般的解决方案是手动限制 Cargo.toml 中的 Serde 版本以匹配其余依赖项:
serde = "0.9"
serde_derive = "0.9"
serde_json = "0.9"
This may not always be possible, in which case you may need to hound the crate owners to upgrade their dependencies.这可能并不总是可行的,在这种情况下,您可能需要追捕 crate 所有者以升级他们的依赖项。
[dependencies]
chrono = "0.3.0"
rocket = "0.2.8"
rocket_codegen = "0.2.8"
serde = "1.0.8"
serde_derive = "1.0.8"
serde_json = "1.0.2"
mysql = "11.1.2"
diesel = { version = "0.13.0", features = ["mysql","chrono"] }
diesel_codegen = { version = "0.13.0", features = ["mysql"] }
dotenv = "0.10.0"
[dependencies.rocket_contrib]
version = "*"
default-features = false
features = ["handlebars_templates"]
rocket_contrib 0.2.8 depends on Serde 0.9, but you have pulled in Serde 1.0. Rocket_contrib 0.2.8 依赖于 Serde 0.9,但你已经引入了 Serde 1.0。 This abridged snippet from
cargo tree
shows the problem: cargo tree
的这个删减片段显示了问题:
reproduction v0.1.0 (file:///private/tmp/reproduction)
├── rocket_contrib v0.2.8
│ ├── handlebars v0.25.3
│ │ └── serde_json v0.9.10
│ │ └── serde v0.9.15
│ ├── serde v0.9.15 (*)
│ └── serde_json v0.9.10 (*)
├── serde v1.0.8 (*)
├── serde_derive v1.0.8
│ ├── serde_derive_internals v0.15.1
└── serde_json v1.0.2 (*)
The upcoming version 0.3 of Rocket should allow using Serde 1.0.即将发布的 Rocket 0.3 版本应该允许使用 Serde 1.0。
[dependencies]
bodyparser = "0.5"
bson = "0.8"
iron = "0.5"
jwt = "0.4"
mongodb = "0.3"
router = "0.5"
rust-crypto = "0.2"
serde = "1.0"
serde_derive = "1.0"
serde_json = "1.0"
time = "0.1"
bodyparser 0.5 depends on Serde 0.8, MongoDB has pulled in 0.9, but the crate and BSON have pulled in Serde 1.0. bodyparser 0.5 依赖于 Serde 0.8,MongoDB 引入了 0.9,但是 crate 和 BSON 引入了 Serde 1.0。 This abridged snippet from
cargo tree
shows the problem: cargo tree
的这个删减片段显示了问题:
reproduction v0.1.0 (file:///private/tmp/reproduction)
├── bodyparser v0.5.0
│ ├── serde v0.8.23
│ └── serde_json v0.8.6
│ └── serde v0.8.23 (*)
├── bson v0.8.0
│ ├── serde v1.0.8
│ ├── serde_json v1.0.2
│ │ └── serde v1.0.8 (*)
├── mongodb v0.3.0
│ ├── textnonce v0.6.0
│ │ ├── serde v0.9.15
│ │ └── serde_derive v0.9.15
├── serde v1.0.8 (*)
├── serde_derive v1.0.8
├── serde_json v1.0.2 (*)
Bodyparser 0.7.0 should support Serde 1.0. Bodyparser 0.7.0应该支持 Serde 1.0。 The state of textnonce is less clear, but that dependency might be a private one, so it might not matter in this case.
textnonce 的状态不太清楚,但这种依赖可能是私有的,因此在这种情况下可能无关紧要。
chrono = "0.4.0"
diesel = { version = "0.13.0", features = [ "chrono", "sqlite" ] }
diesel_codegen = { version = "0.13.0", features = [ "sqlite" ] }
dotenv = "0.9.0"
The current version of Chrono is 0.4.0, but Diesel only knows how to serialize Chrono 0.3.0.目前 Chrono 的版本是 0.4.0,但 Diesel 只知道如何序列化 Chrono 0.3.0。
reproduction v0.1.0 (file:///private/tmp/reproduction)
├── chrono v0.4.0
├── diesel v0.13.0
│ ├── chrono v0.3.0
[dependencies]
blowfish = "0.2.1"
block-cipher-trait = "0.3.0"
reproduction v0.1.0 (file:///private/tmp/reproduction)
├── block-cipher-trait v0.3.0
│── blowfish v0.2.1
├── block-cipher-trait v0.2.0
[dependencies]
piston_window = "0.74.0"
conrod = { version = "0.56.0", features = ["piston"] }
repro v0.1.0 (file:///private/tmp/repro)
├── conrod v0.56.0
│ ├── piston2d-graphics v0.23.0
└── piston_window v0.74.0
├── piston2d-graphics v0.24.0 (*)
[dependencies]
actix-web = "0.6.10"
futures = "0.2.1"
repro v0.1.0 (file:///private/tmp/repro)
├── actix-web v0.6.12
│ ├── actix v0.5.8
│ │ ├── futures v0.1.21
└── futures v0.2.1
RFC 1977 proposes to introduce the notion of public and private dependencies to Cargo. RFC 1977提议将公共和私有依赖的概念引入 Cargo。 If you use a crate that in turn publicly exposes another crate's types, Cargo would ensure that you use a single unified version for the crate with the common types.
如果您使用的 crate 反过来又公开公开了另一个 crate 的类型,Cargo 将确保您为具有通用类型的 crate 使用单个统一版本。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.