Cannot use enum values in JSON without explicit casts

[lukaseder]

Try this:

create domain e as enum ('a', 'b');
select cast ('a' as e);
select json_array(cast('a' as e));

I would expect the query to produce ["a"], but it fails with:

SQL Error [22018] [22018]: Data conversion error converting "ENUM to JSON"

As a workaround, I can cast the enum value back to VARCHAR explicitly, but I think that should work out of the box?

select json_array(cast(cast('a' as e) as varchar));

Is there any other reasonable auto conversion from an enum value to a json value that I might be overlooking?

[katzyn]

Is there any other reasonable auto conversion from an enum value to a json value that I might be overlooking?

There are at least two other possible conversions to 1-based JSON number or 0-based JSON number, but they aren't reasonable from my point of view; people who need them can use a cast and arithmetic operation.

JSON string looks like a reasonable default.

[lukaseder]

There are at least two other possible conversions to 1-based JSON number or 0-based JSON number

I thought about it too. The 0-based JSON number wouldn't work, I think?

select cast (cast ('a' as e) as int);

Produces 1, not 0, so it would have to be consistent with the CAST behaviour.

but they aren't reasonable from my point of view; people who need them can use a cast and arithmetic operation.

Indeed, most people use the enum's string value, e.g. also when inserting into a table containing an enum type:

create table t (e e);
insert into t values ('a');