Calling Your Own UDFs

use better_duck_core::duckdb_scalar;
use better_duck_diesel::DuckDbConnection;
use diesel::expression::functions::define_sql_function;
use diesel::prelude::*;
use diesel::sql_types::Integer;

#[duckdb_scalar(name = "add_one")]
fn add_one_impl(x: i32) -> i32 { x + 1 }

define_sql_function! { fn add_one(x: Integer) -> Integer; }

let mut conn = DuckDbConnection::establish(":memory:")?;
add_one_impl::register(conn.inner_mut())?;  // register on the core connection via inner_mut()

let out: Vec<i32> = nums::table.select(add_one(nums::id)).order(nums::id).load(&mut conn)?;