Rust: sqlite3 のデータを読む (Read)

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

[package]
name = "sqlite3_read"
version = "0.1.0"
edition = "2018"

[dependencies]
rusqlite = "*"

// --------------------------------------------------------------------
/*
    sqlite3_read/src/main.rs

                    Jul/23/2020
*/
// --------------------------------------------------------------------
use std::env;
use rusqlite::{params, Connection, Result};

#[derive(Debug)]
struct City {
    id: String,
    name: String,
    population: i32,
    date_mod: String,
}

fn main() -> Result<()> {
    eprintln!("*** start ***");

    let args: Vec<_> = env::args().collect();

    let file_sqlite3 = &args[1];

    eprintln!("{}",file_sqlite3);

    let conn = Connection::open(file_sqlite3).unwrap();

    let mut stmt = conn.prepare("SELECT id, name, population, date_mod FROM cities")?;
    let city_iter = stmt.query_map(params![], |row| {
        Ok(City {
            id: row.get(0)?,
            name: row.get(1)?,
            population: row.get(2)?,
            date_mod: row.get(3)?,
        })
    })?;

    for city in city_iter {
        println!("{:?}", city.unwrap());
    }

    eprintln!("*** end ***");

    Ok(())
}

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

$ cargo run /var/tmp/sqlite3/cities.db
    Finished dev [unoptimized + debuginfo] target(s) in 0.50s
     Running `target/debug/sqlite3_read /var/tmp/sqlite3/cities.db`
*** start ***
/var/tmp/sqlite3/cities.db
City { id: "t0711", name: "郡山", population: 38415, date_mod: "1956-5-15" }
City { id: "t0712", name: "会津若松", population: 57926, date_mod: "1956-6-8" }
City { id: "t0713", name: "白河", population: 98123, date_mod: "1956-8-17" }
City { id: "t0714", name: "福島", population: 63259, date_mod: "1956-1-21" }
City { id: "t0715", name: "喜多方", population: 21748, date_mod: "1956-9-12" }
City { id: "t0716", name: "二本松", population: 51924, date_mod: "1956-7-5" }
City { id: "t0717", name: "いわき", population: 97125, date_mod: "1956-9-12" }
City { id: "t0718", name: "相馬", population: 63219, date_mod: "1956-3-22" }
City { id: "t0719", name: "須賀川", population: 25781, date_mod: "1956-11-30" }
*** end ***