doing Sqlite3 and PostgreSQL with diesel at once

extern crate chrono;
extern crate diesel;

use super::flextimestamp::FlexTimestamp;
use super::flexuuid::FlexUuid;

use super::models;
use super::schema;
use diesel::pg::PgConnection;
use diesel::prelude::*;
use diesel::sqlite::SqliteConnection;
use dotenv::dotenv;
use std::env;

pub enum DbConnection {
    SqliteConn(SqliteConnection),
    PostgresConn(PgConnection),
}

pub fn db_get_conn() -> DbConnection {
    dotenv().ok();
    let database_url = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
    let ret = if database_url.starts_with("postgres://") {
        let conn = PgConnection::establish(&database_url).expect(&format!(
            "Error connecting to {} (using PostgreSQL)",
            database_url
        ));
        DbConnection::PostgresConn(conn)
    } else {
        let conn = SqliteConnection::establish(&database_url).expect(&format!(
            "Error connecting to {} (using Sqlite3)",
            database_url
        ));
        DbConnection::SqliteConn(conn)
    };
    ret
}

macro_rules! multidb_run {
    ($dbc: expr, $what: expr, $action: tt, $errmsg: expr) => {
        match $dbc {
            DbConnection::SqliteConn(sqlite_conn) => ($what).$action(sqlite_conn).expect($errmsg),
            DbConnection::PostgresConn(pg_conn) => ($what).$action(pg_conn).expect($errmsg),
        }
    };
}

macro_rules! define_db_insert {
    ($fnname: ident, $tblname: ident, $itemtype: ident) => {
        pub fn $fnname(dbc: &DbConnection, new_item: &models::$itemtype) -> usize {
            let new_item = crate::models::$itemtype {
                UpdatedAt: FlexTimestamp::now(),
                ..new_item.clone()
            };
            multidb_run!(
                dbc,
                diesel::insert_into(schema::$tblname::table).values(&new_item),
                execute,
                &format!("Error saving new {} - {:?}", stringify!($itemtype), new_item)
            )
        }
    };
}


define_db_insert!(db_insert_post, Posts, NewPost);
define_db_insert!(db_insert_comment, Comments, NewComment);