How to use sqlx::Type with more complex scalar types?

[thomaseizinger]

Reposting #1493.

---

I have a Rust type that consists of multiple fields, in particular it looks like this:

pub struct BitMexPriceEventId {
    /// The timestamp this price event refers to.
    timestamp: OffsetDateTime,
    digits: usize,
}

This type has a Display and FromStr implementation and hence can represent itself as a single scalar value. I would like to store this value in the database using its string representation AND use this type directly within SQL queries (which means sqlx needs to know how to handle it).

What is the best way of supporting this? Perhaps this would work?

#[derive(sqlx::Type)]
#[sqlx(display_fromstr)] // name subject to bike-shedding
pub struct BitMexPriceEventId {
    /// The timestamp this price event refers to.
    timestamp: OffsetDateTime,
    digits: usize,
}

[thomaseizinger]

Found a way that works:

macro_rules! impl_sqlx_type_display_from_str {
    ($ty:ty) => {
        impl sqlx::Type<sqlx::Sqlite> for $ty {
            fn type_info() -> sqlx::sqlite::SqliteTypeInfo {
                String::type_info()
            }
        }

        impl<'q> sqlx::Encode<'q, sqlx::Sqlite> for $ty {
            fn encode_by_ref(
                &self,
                args: &mut Vec<sqlx::sqlite::SqliteArgumentValue<'q>>,
            ) -> sqlx::encode::IsNull {
                self.to_string().encode_by_ref(args)
            }
        }

        impl<'r> sqlx::Decode<'r, sqlx::Sqlite> for $ty {
            fn decode(
                value: sqlx::sqlite::SqliteValueRef<'r>,
            ) -> Result<Self, sqlx::error::BoxDynError> {
                let string = String::decode(value)?;
                let value = string.parse()?;

                Ok(value)
            }
        }
    };
}