带有 Postgres 的 Rust 柴油机库中的时间戳

Question

我一直在查看 Rust 的 Diesel ORM today by following along on this walk-through，但无法使 Timestamp 正常工作。

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
}

（我读到有一个 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))
}

但这些是我在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 是由于 infer_schema 不知道如何解释已经在 table 中的 Postgresql 类型。至于第二个，我想也许如果显式导入 Timestamp 类型，我可以用它创建一个 Post 结构。

有什么明显的地方我做错了吗？

顺便说一句，我对 Rust 很陌生，Diesel 使用了相当多的代码生成，所以很容易迷路，但我认为这应该是一件很容易完成的事情。

编辑：

我用 timestamp with time zone 创建了 table，它看起来像 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，并消除了关于 Timestamp 未定义的错误。我还意识到我需要 #[derive(Queryable)] 在每个要派生的结构之上。以下编译正常，但之前 Timestamptz 的错误仍然存在：

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
}

Answer 1

请检查 ui

中的数据类型

"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 未定义或不在范围内 [E0412] src/models.rs:17 发布更新：时间戳“

可能时间戳不是定义词。

Answer 2

diesel::sql_types are markers to represent various SQL datatypes for your schema. They should never be used in your own structs. What you need is a type which implements diesel::deserialize::FromSql<diesel::sql_types::Timestamp, diesel::pg::Pg> (docs: FromSql, Timestamp, Pg 中的所有类型）。有两种类型实现了该特征。

第一个是 std::time::SystemTime，它不需要额外的依赖项，但没有很多功能。

第二个是 chrono::NaiveDateTime. This is probably the type you want. In order to use it, you'll need to add chrono 到您的依赖项，并更改 Cargo.toml 中的柴油线以包含计时功能，因此它看起来像 diesel = { version = "0.7.0", features = ["postgres", "chrono"] }

（从技术上讲，还有第三种类型，即 diesel::data_types::PgTimestamp 但这几乎肯定不是您想要的，因为该结构只是数据库中时间戳的字面表示，因此其他类型不必担心关于原始字节）

带有 Postgres 的 Rust 柴油机库中的时间戳

Timestamp in Rust's Diesel Library with Postgres

postgresql

rust

rust-diesel