Rust dieselでString以外の型のModel定義

model.rs

use super::merchants::Merchant;
use crate::schema::charge_logs;
use chrono::NaiveDateTime;
use diesel::{
  deserialize::{self, FromSql},
  expression::Expression,
  pg::Pg,
  serialize::{self, Output, ToSql},
  sql_types::Bpchar,
  AsExpression, Associations, Identifiable, Insertable, Queryable,
};
use std::io::Write;

#[derive(Debug, PartialEq, FromSqlRow, AsExpression)]
pub enum CurrencyCode {
  USD,
  Unsupported(String),
}

impl Expression for CurrencyCode {
  type SqlType = Bpchar;
}

impl ToSql<Bpchar, Pg> for CurrencyCode {
  fn to_sql<W: Write>(&self, out: &mut Output<W, Pg>) -> serialize::Result {
    let t = match *self {
      CurrencyCode::USD => "usd",
      CurrencyCode::Unsupported(_) => "---",
    };
    <&str as ToSql<Bpchar, Pg>>::to_sql(&t, out)
  }
}

impl FromSql<Bpchar, Pg> for CurrencyCode {
  fn from_sql(bytes: Option<&[u8]>) -> deserialize::Result<Self> {
    match (<String as FromSql<Bpchar, Pg>>::from_sql(bytes)?).as_ref() {
      "usd" => Ok(CurrencyCode::USD),
      x => Ok(CurrencyCode::Unsupported(x.to_owned())),
    }
  }
}

#[derive(Queryable, Insertable, Identifiable, Associations, Debug)]
#[belongs_to(Merchant, foreign_key = "charge_id")]
#[primary_key(created_at)]
#[table_name = "charge_logs"]
pub struct ChargeLog {
  pub created_at: NaiveDateTime,
  pub amount: i32,
  pub currency_code: CurrencyCode,
  pub charge_id: String,
}