如何在 Rust 中格式化传递给 mysql crate 的 Pool::new 的字符串

Question

我正在尝试执行板条mysql箱文档的基本示例的开头，但使用格式化字符串而不是完全硬编码的字符串：

use mysql::*;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    // These will be read from a config file
    let user = "root";
    let pw = "password";
    let host = "localhost";
    let port = 3307;
    let db = "db_name";

    let url = format!("mysql://{user}:{pw}@{host}:{port}/{db}");
    let pool = Pool::new(url)?; // Error at this line
    let mut conn = pool.get_conn()?;
    
    Ok(())
}

但是我收到这个错误：

error[E0277]: the trait bound `Opts: From<std::string::String>` is not satisfied
   --> src/main.rs:13:23
    |
13  |     let pool = Pool::new(url)?;
    |                --------- ^^^ the trait `From<std::string::String>` is not implemented for `Opts`
    |                |
    |                required by a bound introduced by this call

我是 Rust 新手，整个晚上都在寻找解决方案。format!为什么没有执行的输出From<String>？如何传递格式化字符串Pool::new而不是硬编码字符串？谢谢

Answer 1

我会构建一个OptsBuilder而不是连接字符串：

use mysql::*;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    // These will be read from a config file
    let user = "root";
    let pw = "password";
    let host = "localhost";
    let port = 3307;
    let db = "db_name";
    let opts = OptsBuilder::new()
        .user(Some(user))
        .pass(Some(pw))
        .ip_or_hostname(Some(host))
        .tcp_port(port)
        .db_name(Some(db));
    let pool = Pool::new(opts)?;
    let mut conn = pool.get_conn()?;

    Ok(())
}

但如果你真的想要，你可以将生成String的转换format!为 a &str，因为涉及泛型，最简单的方法是使用.as_str()：

    let url = format!("mysql://{user}:{pw}@{host}:{port}/{db}");
    let pool = Pool::new(url.as_str())?;