How to implement custom PostgreSQL range?

[zxcqirara]

I need to store RangeInclusive in postgresql database but it does not seem to be implemented fully. I decided to write my own implementation, here is my code:

#[derive(Debug, Serialize, Deserialize)]
pub struct MyRangeInclusive(RangeInclusive<u16>);

impl Into<RangeInclusive<u16>> for MyRangeInclusive {
	fn into(self) -> RangeInclusive<u16> {
		self.0
	}
}

impl ToSql<Range<Integer>, Pg> for MyRangeInclusive {
	fn to_sql<'b>(&'b self, out: &mut Output<'b, '_, Pg>) -> diesel::serialize::Result {
		let (start, end) = self.0.clone().into_inner();
		write!(out, "[{},{}]", start, end)?;

		Ok(IsNull::No)
	}
}

impl FromSql<Range<Integer>, Pg> for MyRangeInclusive {
	fn from_sql(bytes: <Pg as Backend>::RawValue<'_>) -> diesel::deserialize::Result<Self> {
		let range_str = std::str::from_utf8(bytes.as_bytes())?;

		let range_str = range_str.trim_matches(|c| c == '[' || c == ']');
		let mut parts = range_str.split(',');

		let start: u16 = parts.next().ok_or_else(|| "Invalid range format")?.parse()?;
		let end: u16 = parts.next().ok_or_else(|| "Invalid range format")?.parse()?;

		Ok(MyRangeInclusive(start..=end))
	}
}

but when I tried to use it in table model:

#[derive(Insertable)]
#[diesel(table_name = crate::path::to::schema)]
#[diesel(check_for_backend(diesel::pg::Pg))]
pub struct NewRow {
	pub range: MyRangeInclusive
}

it threw an error:

error[E0277]: the trait bound `MyRangeInclusive: diesel::Expression` is not satisfied
  --> src/database/model.rs:15:10
   |
15 | #[derive(Insertable)]
   |          ^^^^^^^^^^ the trait `diesel::Expression` is not implemented for `MyRangeInclusive`, which is required by `MyRangeInclusive: AsExpression<diesel::sql_types::Range<Integer>>`
   |
   = help: the following other types implement trait `diesel::Expression`:
             &'a T
             (T0, T1)
             (T0, T1, T2)
             (T0, T1, T2, T3)
             (T0, T1, T2, T3, T4)
             (T0, T1, T2, T3, T4, T5)
             (T0, T1, T2, T3, T4, T5, T6)
             (T0, T1, T2, T3, T4, T5, T6, T7)
           and 196 others
   = note: required for `MyRangeInclusive` to implement `AsExpression<diesel::sql_types::Range<Integer>>`
   = note: this error originates in the derive macro `Insertable` (in Nightly builds, run with -Z macro-backtrace for more info)

But documentation declares that if I have implemented ToSql then (logically) it should be implemented AsExpression

[weiznich]

To cite from the ToSql documentation:

Any types which implement this trait should also #[derive(AsExpression)].

That's not the case for your implementation. Adding this derive should fix your issue.
For loading data I suggest checking out the FromSql docs, they state a similar requirement.

[zxcqirara]

Oh, thank you, that maked it work

[zxcqirara]

It started to throw a new error:

the trait `diesel::deserialize::FromSqlRow<_, _>` is not implemented for `MyRow`, which is required by `SelectStatement<FromClause<table>, query_builder::select_clause::SelectClause<diesel::expression::select_by::SelectBy<MyRow, _>>>: diesel_async::methods::LoadQuery<'_, _, MyRow>

#[derive(Queryable, Selectable, Serialize, Deserialize)]
#[diesel(table_name = crate::path::to::schema)]
#[diesel(check_for_backend(diesel::pg::Pg))]
pub struct MyRow {
	pub id: i32,
	pub range: MyRangeInclusive
}

...

let test = my_table::table
	.select(MyRow::as_select())
	.load::<MyRow>(&mut conn)
	.await?;

[weiznich]

Let me cite my last answer again:

For loading data I suggest checking out the FromSql docs, they state a similar requirement.

[zxcqirara]

It is in my derives but nvm, I provided Pool, not PooledConnection, I think I fixed it