I managed to work around this by implemeting an error type enum FooError with a variant like Foo(String) that I then implement From diesel::result::Error` for --

impl From<diesel::result::Error> for FooError {
    fn from(error: diesel::result::Error) -> Self {
        FooError::Foo(error.to_string())
    }
}

I then can use this error type as the error value in my transaction - Can anyone tell me why this From<diesel::result::Error> needs to be implemented for this transaction method error? I guess I need help better understand handling errors in general

@Aceeri This should do the trick without renaming the database column:

table! {
    posts {
        id -> Integer,
        /// This column is named `mytype` but references the table `type` column.
        #[sql_name = "type"]
        mytype -> Text,
    }
}

(Literally copied from the documentation of the table! macro)

I'm trying to implement FromSql<Text, DB> for a custom type, but I'm having trouble resolving this compiler error:

error[E0271]: type mismatch resolving `<DB as diesel::backend::Backend>::RawValue == [u8]`
   --> src/game/mod.rs:289:17
    |
289 |         let s = <String as FromSql<Text, DB>>::from_sql(bytes)?;
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected associated type, found slice
    |
    = note: expected type `<DB as diesel::backend::Backend>::RawValue`
               found type `[u8]`
    = note: required because of the requirements on the impl of `diesel::deserialize::FromSql<diesel::sql_types::Text, DB>` for `*const str`
    = note: required because of the requirements on the impl of `diesel::deserialize::FromSql<diesel::sql_types::Text, DB>` for `std::string::String`
    = note: required by `diesel::deserialize::FromSql::from_sql`

for reference, the full trait implementation:

impl<DB> FromSql<Text, DB> for Hand
where
    DB: Backend,
{
    fn from_sql(bytes: Option<&DB::RawValue>) -> deserialize::Result<Self> {
        let s = <String as FromSql<Text, DB>>::from_sql(bytes)?;
        let hand = Hand::parse(s);
        Ok(hand)
    }
}