如何在 Rust 中从 PostgreSQL 读取带有时区（timestamptz）值的时间戳？

Question

timestamptz当使用 postgres 版本 0.17.0 和 Rust 1.40.0 时，正确的 Rust 数据类型是什么？

我阅读了文档，Timestamp但不知道这意味着什么或如何实现它。

0.17.0-alpha.1 的自述文件有一个表，其中表示timezone对应于 Rust 类型 time::Timespec或，chrono::DateTime<Utc>但两者都不适合我。

当我尝试使用 Cargo.toml 中规定的功能时：

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

我收到此错误：

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

---

这是一些功能代码和相应的依赖项。我希望能够读取并打印每行的时区（注释掉）

主程序.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(())
}

取消注释

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

the package `mypackage` depends on `postgres`, with features: `with-time, with-chrono` but `postgres` does not have these features.

取消注释

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

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"

此链接说要使用time = "0.1.14". 最新版本也失败 https://crates.io/crates/postgres/0.17.0-alpha.1

Answer 1

一旦您知道哪些功能可用，就可以相当直接地看出您需要使用该with-chrono-0_4功能。

use chrono::{DateTime, Utc}; // 0.4.10
use postgres::{Client, Error, NoTls}; // 0.17.0, features = ["with-chrono-0_4"]

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

    client.simple_query(
        r#"
        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: DateTime<Utc> = row.get(1);
        dbg!(name, timestamp);
    }

    Ok(())
}

[src/main.rs:20] name = "bob"
[src/main.rs:20] timestamp = 2020-01-16T01:21:58.755804Z