Fetching fields with Mysql crate in Rust

rust-mysql.rs

#[macro_use]
use crate::mysql::*;
use crate::mysql::prelude::*;
use crate::errors::Error;

#[derive(Debug)]
pub struct ConnectorMysql {

}

#[derive(Debug)]
pub struct ConnectorPostgres {
  
}

#[derive(Debug)]
struct Connection {

}

pub trait Fetch<ReturnType> {
  fn call_db(&self) -> ReturnType;
}

#[derive(Debug)]
pub struct Data {
  host: String,
  user: String
}

impl Fetch<Vec<Data>> for ConnectorMysql
{
  fn call_db(&self) -> Vec<Data> {
    let url = "mysql://root:a@localhost:3306/";
    let pool = Pool::new(url).unwrap();
    let mut conn = pool.get_conn().unwrap();

    let mut stmt = conn.prep(r#"select host, user from mysql.user"#).unwrap();
    let result: Vec<Data> = conn.exec_iter(stmt, ()).map(|result| {
      result.map(|x| x.unwrap()).map(|row| {
        let (host, user) = mysql::from_row(row);
        Data {
          host,
          user
        }
      }).collect()
    }).unwrap();

    result
  }
} 

impl Fetch<String> for ConnectorPostgres
{
  fn call_db(&self) -> String {
    panic!("Err: {:#?}", Error::NotImplementedError)
  }
}

pub fn fetch<ConnectorType, ReturnType>(connector: &ConnectorType) -> ReturnType
where
  ConnectorType: Fetch<ReturnType>
{
  connector.call_db()
}