Rust: Redis のデータを更新 (Update)

$ tree -L 2
.
├── Cargo.lock
├── Cargo.toml
├── src
│   └── main.rs
└── target
    └── debug

[package]
name = "redis_update"
version = "0.1.0"
edition = "2018"

#

[dependencies.redis]
version = "*"

[dependencies]
tokio = { version = "0.2", features = ["full"] }
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"
chrono = "0.4"

// --------------------------------------------------------------------
/*
    redis_update/src/main.rs

                    Jul/22/2020
*/
// --------------------------------------------------------------------
use std::env;
extern crate redis;
use redis::{Commands};
use chrono::{Local, Date};
use serde_json::json;

// --------------------------------------------------------------------
fn main() -> Result<(), Box<dyn std::error::Error>>  {
    eprintln! ("*** 開始 ***");

    let args: Vec<_> = env::args().collect();
    let key_in = &args[1];
    let population_in = &args[2];
    println! ("{}\t{}",key_in,population_in);

    let client = redis::Client::open("redis://localhost/").expect("url error");
    let mut conn = client.get_connection().expect("connect error");

    let res = conn.get(key_in.to_string());

    let answer: String = res.unwrap();

    let json: serde_json::Value = serde_json::from_str(&answer)?;

    let obj = json.as_object().unwrap();

    println! ("{}",obj["name"].to_string());
    println! ("{}",obj["population"].to_string());
    println! ("{}",obj["date_mod"].to_string());

    let date_mod: Date<Local> = Local::today();
    println!("{}", date_mod);

    let pp_in : i32 = population_in.parse().unwrap();
    let obj_new = json!({
        "name": obj["name"],
        "population": pp_in,
        "date_mod": date_mod.to_string()
        });

    let json_str = obj_new.to_string();
    println!("{}",json_str);

    let _: ()  = conn.set(key_in.to_string(), json_str).unwrap();

    eprintln! ("*** 終了 ***");

    Ok(())
}

// --------------------------------------------------------------------

cargo build

cargo run t1857 5128900