Split a table of customers into CSVs by state

main.rs

use tokio_postgres::{NoTls, Client};

type Whoops = Box<dyn std::error::Error>;

const BR_STATES: [&str; 27] = ["AC","AL","AP","AM","BA","CE","DF","ES","GO","MA","MT","MS","MG","PA","PB","PR","PE","PI","RJ","RN","RS","RO","RR","SC","SP","SE","TO"];

async fn query_state(client: &Client, state: &str) -> Result<String, Whoops> {
    let rows = client
        .query("select distinct email from customer where state = $1::TEXT and email <> ''", &[&state])
        .await?;

    let mut wtr = csv::Writer::from_path(format!("var/{}.csv", state))?;
    wtr.write_record(&["email"]);

    rows.iter().for_each(|row| {
       let email: &str = row.get(0);
       wtr.write_record(&[email.to_lowercase()]);
    });

    Ok(format!("{} => {}", state, rows.len()))
}

#[tokio::main]
async fn main() -> Result<(), Whoops> {
    let pgsql_url = std::env::var("PGSQL_URL").unwrap();
    let (client, conn) = tokio_postgres::connect(pgsql_url.as_str(), NoTls).await?;

    tokio::spawn(async move {
        if let Err(e) = conn.await {
            eprintln!("{}", e);
        }
    });

    let results = BR_STATES
        .iter()
        .map(|state| query_state(&client, state));

    let results = futures::future::join_all(results).await;

    println!("{:?}", results);

    Ok(())
}