Enum with integer in DB

room_agent.rs

use uuid::Uuid;

use models::{Agent, Room};
use schema::room_agent;

#[derive(Associations, Queryable, Debug)]
#[table_name = "room_agent"]
#[belongs_to(Agent)]
#[belongs_to(Room)]
pub struct RoomAgent {
    pub id: Uuid,
    pub agent_id: Uuid,
    pub room_id: Uuid,
    pub state: State,
}

#[derive(Insertable, Debug)]
#[table_name = "room_agent"]
pub struct NewRoomAgent {
    pub agent_id: Uuid,
    pub room_id: Uuid,
    pub state: State,
}

impl NewRoomAgent {
    pub fn new(agent_id: Uuid, room_id: Uuid) -> NewRoomAgent {
        NewRoomAgent {
            agent_id,
            room_id,
            state: State::Pending,
        }
    }
}

#[derive(AsExpression, FromSqlRow, Copy, Clone, Debug)]
#[sql_type = "Int4"]
#[repr(u32)]
pub enum State {
    Pending = 0,
    Active = 1,
}

use diesel::deserialize::{self, FromSql};
use diesel::pg::Pg;
use diesel::sql_types::{Int4, Integer};

impl FromSql<Integer, Pg> for State {
    fn from_sql(bytes: Option<&[u8]>) -> deserialize::Result<Self> {
        match <i32 as FromSql<Integer, Pg>>::from_sql(bytes)? {
            0 => Ok(State::Pending),
            1 => Ok(State::Active),
            n => Err(format!("unknown kind: {}", n).into()),
        }
    }
}

use diesel::serialize::{self, Output, ToSql};
use std::io::Write;

impl ToSql<Integer, Pg> for State {
    fn to_sql<W: Write>(&self, out: &mut Output<W, Pg>) -> serialize::Result {
        let x = *self as i32;
        ToSql::<Int4, Pg>::to_sql(&x, out)
    }
}