Using Option<T> with Diesel's Insertable trait

Question

I have the following model:

use diesel::prelude::*;

use crate::schema::category;

#[derive(Debug, Identifiable, Queryable)]
#[table_name = "category"]
pub struct Category {
    pub id: i64,
    pub name: String,
    pub description: String,
    pub parent_id: Option<i64>,
}

#[derive(Debug, Insertable)]
#[table_name = "category"]
pub struct NewCategory<'a> {
    pub name: &'a str,
    pub description: &'a str,
    pub parent_id: &'a Option<i64>,
}

and schema.rs:

table! {
    category (id) {
        id -> Integer,
        name -> Text,
        description -> Text,
        parent_id -> Nullable<Integer>,
    }
}

However, when I try to compile this code, I get the following errors:

error[E0277]: the trait bound `std::option::Option<i64>: diesel::Expression` is not satisfied
  --> src/models/categories.rs:15:17
   |
15 | #[derive(Debug, Insertable)]
   |                 ^^^^^^^^^^ the trait `diesel::Expression` is not implemented for `std::option::Option<i64>`
   |
   = note: required because of the requirements on the impl of `diesel::Expression` for `&std::option::Option<i64>`

error[E0277]: the trait bound `std::option::Option<i64>: diesel::Expression` is not satisfied
  --> src/models/categories.rs:15:17
   |
15 | #[derive(Debug, Insertable)]
   |                 ^^^^^^^^^^ the trait `diesel::Expression` is not implemented for `std::option::Option<i64>`
   |
   = note: required because of the requirements on the impl of `diesel::Expression` for `&'a std::option::Option<i64>`

What do I need to get this to work? I've looked around, but the only similar issue that I've found is when someone had more than 16 columns in their table, which is not the case here.

Answer 1

Modify pub parent_id: &'a Option<i64> to place the &'a inside of the Option: pub parent_id: Option<&'a i64>.