Document how to use Vec<T: ToSql> with query_raw

[runfalk]

I've have some issues with a dynamically generated SQL statement and query_raw. My parameters are Vec<String>.

I tried different variations on how to pass it, and the only solution I found was:

use tokio_postgres::{NoTls, Error};
use tokio_postgres::types::ToSql;

#[tokio::main]
async fn main() -> Result<(), Error> {
    let (client, connection) = tokio_postgres::connect("<redacted>", NoTls).await?;

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

    // The explicit type declaration is very important, Box<String> will not work
    let params: Vec<Box<dyn ToSql>> = vec![Box::new("param".to_owned())];
    client
        .query_raw("SELECT $1::TEXT", params.iter().map(|x| x.as_ref()))
        .await?;
    Ok(())
}

Is there a better way?

[sfackler]

If you have a Vec<String>, you can do params.iter().map(|s| s as &dyn ToSql) I believe.

[runfalk]

Thank you! That seems way more reasonable.

For reference this is the new code:

use tokio_postgres::{NoTls, Error};
use tokio_postgres::types::ToSql;

#[tokio::main]
async fn main() -> Result<(), Error> {
    let (client, connection) = tokio_postgres::connect("<redacted>", NoTls).await?;

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

    let params: Vec<String> = vec!["param".to_owned()];
    client
        .query_raw("SELECT $1::TEXT", params.iter().map(|x| x as &dyn ToSql))
        .await?;
    Ok(())
}

Would you like a PR to add some information to the documentation?

[sfackler]

Sure!