How can I read a timestamp with timezone (timestamptz) value from PostgreSQL in Rust?

Question

What's the right Rust data type to use for a timestamptz when using postgres version 0.17.0 with Rust 1.40.0?

I read the docs for Timestamp but have no idea what this means or how to implement it.

The readme for 0.17.0-alpha.1 has a table which says that timezone corresponds to Rust types time::Timespec or chrono::DateTime<Utc> but neither works for me.

When I try to use the stipulated features in my Cargo.toml using:

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

I get this error:

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

Here's some functional code and corresponding dependencies. I want to be able to read and print the timezone per row (commented out)

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(())
}

Uncommenting

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`

Uncommenting

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>`

Cargo.toml

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

This link says to use time = "0.1.14". latest version also fails https://crates.io/crates/postgres/0.17.0-alpha.1

0.17.0 is newer than 0.17.0-alpha.1; why would you continue using the alpha? — Shepmaster, Jan 16 '20 at 01:09
@Shepmaster i was only using 0.17.0-alpha.1 cos its docs have a "Type Correspondence" table and features info. thank you for your help/answers!! — stuart, Jan 16 '20 at 02:01

Shepmaster · Accepted Answer · 2021-01-17T17:51:38.233

Once you know what features are available, it's reasonably direct to see that you need to use the with-chrono-0_4 feature.

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

Thanks; this worked for me: [dependencies.postgres] version = "0.19.5" features = ["with-chrono-0_4", "with-time-0_3"] — Aaron West, Apr 09 '23 at 16:57

score 0 · Answer 2 · edited Jan 16 '20 at 01:12

Thanks to https://github.com/sfackler/rust-postgres/issues/211, this works using version 0.15.0 of the postgres crate, but I'd like a solution using version 0.17.0.

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);
    }
}

Output:

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"

How can I read a timestamp with timezone (timestamptz) value from PostgreSQL in Rust?

2 Answers2

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