Question

我今天一直在关注Rust的Diesel ORM跟随this walk-through，我无法让Timestamp工作。

Cargo.toml

[dependencies]
diesel = { version = "0.6.2", features = ["chrono"] }
diesel_codegen = { version = "0.6.2", default-features = false, features = ["nightly", "postgres"] }
dotenv = "0.8.0"
dotenv_macros = "0.8.0"

models.rs

#[derive(Queryable)]

pub struct Author {
    pub id: i32,
    pub first_name: String,
    pub last_name: String,
    pub email: String
}

pub struct Post {
    pub id: i32,
    pub author: Author,
    pub title: String,
    pub body: String,
    pub published: bool,
    pub created: Timestamp,
    pub updated: Timestamp
}

（我读到有diesel::types::Timestamp类型）

lib.rs

#![feature(custom_derive, custom_attribute, plugin)]
#![plugin(diesel_codegen, dotenv_macros)]

#[macro_use]
extern crate diesel;
extern crate dotenv;

pub mod schema;
pub mod models;

use diesel::prelude::*;
use diesel::types::Timestamp;
use diesel::pg::PgConnection;
use dotenv::dotenv;
use std::env;

pub fn establish_connection() -> PgConnection {
    dotenv().ok();

    let database_url = env::var("DATABASE_URL").
        expect("DATABASE_URL must be set");
    PgConnection::establish(&database_url).
        expect(&format!("Error connecting to {}", database_url))
}

但这些是我尝试使用它时遇到的错误：

<diesel macros>:5:1: 5:71 note: in this expansion of table_body! (defined in <diesel macros>)
src/schema.rs:1:1: 1:40 note: in this expansion of table! (defined in <diesel macros>)
src/schema.rs:1:1: 1:40 note: in this expansion of infer_schema! (defined in src/lib.rs)
src/lib.rs:1:1: 1:1 help: run `rustc --explain E0412` to see a detailed explanation
src/lib.rs:1:1: 1:1 help: no candidates by the name of `Timestamptz` found in your project; maybe you misspelled the name or forgot to import an external crate?
src/lib.rs:1:1: 1:1 error: type name `Timestamptz` is undefined or not in scope [E0412]
src/lib.rs:1 #![feature(custom_derive, custom_attribute, plugin)]

...

<diesel macros>:38:1: 38:47 note: in this expansion of column! (defined in <diesel macros>)
<diesel macros>:5:1: 5:71 note: in this expansion of table_body! (defined in <diesel macros>)
src/schema.rs:1:1: 1:40 note: in this expansion of table! (defined in <diesel macros>)
src/schema.rs:1:1: 1:40 note: in this expansion of infer_schema! (defined in src/lib.rs)
src/lib.rs:1:1: 1:1 help: run `rustc --explain E0412` to see a detailed explanation
src/lib.rs:1:1: 1:1 help: no candidates by the name of `Timestamptz` found in your project; maybe you misspelled the name or forgot to import an external crate?
src/models.rs:16:18: 16:27 error: type name `Timestamp` is undefined or not in scope [E0412]
src/models.rs:16     pub created: Timestamp,
                              ^~~~~~~~~
src/models.rs:16:18: 16:27 help: run `rustc --explain E0412` to see a detailed explanation
src/models.rs:16:18: 16:27 help: you can import it into scope: `use diesel::types::Timestamp;`.
src/models.rs:17:18: 17:27 error: type name `Timestamp` is undefined or not in scope [E0412]
src/models.rs:17     pub updated: Timestamp
                              ^~~~~~~~~

看起来第一个错误Timestamptz是infer_schema不知道如何解释Postgresql类型的结果，该类型已经在表中。至于第二个，我想也许如果明确导入Timestamp类型，我可以用它创建一个Post结构。

有什么明显的事我在这里做错了吗？

顺便说一下，我对Rust来说很新，Diesel使用了相当多的代码生成，因此很容易迷失，但我认为这应该是一个简单易行的事情。

修改：

我使用timestamp with time zone创建表格，看起来像may not be supported yet：

CREATE TABLE post (
    ...
    created timestamp with time zone NOT NULL,
    updated timestamp with time zone
)

编辑2：

我将 models.rs 更改为如下所示，并删除了有关Timestamp未定义的错误。我也意识到我需要在每个结构上方#[derive(Queryable)]得到Timestamptz。以下编译正常，但以前的use diesel::types::Timestamp; #[derive(Queryable)] pub struct Author { pub id: i32, pub first_name: String, pub last_name: String, pub email: String } #[derive(Queryable)] pub struct Post { pub id: i32, pub author: Author, pub title: String, pub body: String, pub published: bool, pub created: Timestamp, pub updated: Timestamp }错误仍然存在：

/football/players/someplayer

Answer 1

diesel::sql_types中的所有类型都是表示架构的各种SQL数据类型的标记。它们永远不应该用在你自己的结构中。您需要的是一种实现diesel::deserialize::FromSql<diesel::sql_types::Timestamp, diesel::pg::Pg>的类型（文档：FromSql，Timestamp，Pg）。有两种类型可以实现这种特性。

第一个是std::time::SystemTime，它不需要额外的依赖关系，但不具备大量功能。

第二个是chrono::NaiveDateTime。这可能是你想要的类型。为了使用它，您需要将chrono添加到您的依赖项中，并更改Cargo.toml中的柴油线以包含计时功能，因此它看起来像{{1 }}

（从技术上来说，第三种类型是diesel::data_types::PgTimestamp，但这几乎肯定不是你想要的，因为该结构只是数据库中时间戳的文字表示，所以其他类型＃39; t不得不担心原始字节）

Answer 2

请检查ui的数据类型

＆＃34; src / models.rs:16：18：16：27帮助：您可以将其导入范围：use diesel::types::Timestamp;。 src / models.rs:17:18:17:27错误：类型名称Timestamp未定义或未在范围内[E0412] src / models.rs:17 pub更新：时间戳＆＃34;

也许时间戳不是定义单词。

使用Postgres的Rust柴油库中的时间戳

2 个答案: