如何在Rust中读取PostgreSQL时区？

Question

tldr：Rust如何从PostgreSQL读取timestamp with timezone（timestamptz）值？

**使用最新的当前板条箱：postgres = "0.17.0" **

aka使用哪种正确的Rust数据类型？

这里有一些我一直在浏览的文档/示例，这些文档/示例对我不起作用：

无用链接1

https://docs.rs/postgres/0.17.0/postgres/types/enum.Timestamp.html

我是生锈的新手，不知道这意味着什么或如何实现

无用链接2

https://crates.io/crates/postgres/0.17.0-alpha.1

这里的表说postgres类型timezone对应于rust类型：time::Timespec或chrono::DateTime<Utc>。没人为我工作。另外，当我尝试使用features中规定的Cargo.toml时，出现此错误：

软件包mypackage取决于postgres，具有以下特征：with-time, with-chrono但postgres不具有这些特征。

使用：

[dependencies]
postgres = {version="0.17.0-alpha.1", features=["with-chrono", "with-time"]}

无用链接3

https://github.com/sfackler/rust-postgres/issues/211

此可能会工作（更新：它有效，请参见我的答案），但我想使用当前的postgres = "0.17.0"条板箱解决方案

---

这里是一些功能代码和相应的依赖关系。我希望能够读取和打印每行的时区（注释掉）

main.rs

use postgres::{Client, Error, NoTls};
extern crate chrono;
use chrono::{DateTime, Local, NaiveDateTime, TimeZone, Utc};
extern crate time;
use time::Timespec;

pub fn main() -> Result<(), Error> {
    let mut client = Client::connect("host=localhost user=postgres", NoTls)?;

    client.simple_query(
        "
        CREATE TABLE mytable (
            name        text NOT NULL,
            timestamp   timestamptz NOT NULL)",
    )?;

    client.execute("INSERT INTO mytable VALUES ('bob', now());", &[])?;

    for row in client.query("SELECT * FROM mytable", &[])? {
        let name: &str = row.get(0);
        // let timestamp: chrono::DateTime<Utc> = row.get(1);   //doesnt work
        // let timestamp: Timespec = row.get(1);  //doesnt work
        println!("name: {}", name);
        // println!("timestamp: {}", timestamp);
    }

    Ok(())
}

Cargo.toml

...
[dependencies]
postgres = "0.17.0"
chrono = "0.4.10"
time = "0.1.14"

此链接表示使用time = "0.1.14"。最新版本也失败https://crates.io/crates/postgres/0.17.0-alpha.1

锈版本：

> rustc --version
rustc 1.40.0 (73528e339 2019-12-16)

谢谢您的阅读/考虑！任何帮助将不胜感激

---

每条注释掉的尝试行的错误消息：

1

let timestamp: Timespec = row.get(1);  //doesnt work

->

error[E0277]: the trait bound `time::Timespec: postgres_types::FromSql<'_>` is not satisfied  
--> src/main.rs:30:39  | 30 | 
let timestamp: Timespec = row.get(1);   //doesnt work     
                              ^^^ the trait `postgres_types::FromSql<'_>` is not implemented for `time::Timespec`

2

let timestamp: chrono::DateTime<Utc> = row.get(1);   //doesnt work

->

error[E0277]: the trait bound `chrono::DateTime<chrono::Utc>: postgres_types::FromSql<'_>` is not satisfied
--> src/main.rs:29:52 29 |         
let timestamp: chrono::DateTime<Utc> = row.get(1);   //doesnt work
                                           ^^^ the trait `postgres_types::FromSql<'_>` is not implemented for `chrono::DateTime<chrono::Utc>`

Answer 1

作为一个令人沮丧的临时解决方案，它可以使用较旧的版本postgres = "0.15.0"使用

main.rs

extern crate postgres;
use postgres::{Connection, TlsMode};

extern crate chrono;
use chrono::{DateTime, Local, NaiveDateTime, TimeZone, Utc};

fn main() {
    let conn = Connection::connect("postgresql://postgres@localhost:5432", TlsMode::None).unwrap();

    conn.execute(
        "CREATE TABLE person (
             name            VARCHAR NOT NULL,
             timestamp       timestamptz
        )",
        &[],).unwrap();

    conn.execute("INSERT INTO person VALUES ('bob', now());", &[]).unwrap();

    for row in &conn.query("SELECT * FROM person", &[]).unwrap() {
        let name: String = row.get(0);
        let timestamp: chrono::DateTime<Utc> = row.get(1);
        println!("name: {}", name);
        println!("timestamp: {}", timestamp);
    }
}

输出：

name: bob
timestamp: 2020-01-15 23:56:05.411304 UTC

Cargo.toml

...
[dependencies]
postgres = { version = "0.15", features = ["with-chrono"] }
chrono = "0.4.10"
time = "0.1.14"

感谢https://github.com/sfackler/rust-postgres/issues/211