Is it a bad practice to query pg_type for enums on a regular basis?

Question

In Postgres, I'm thinking of query pg_type for an up-to-date list of enumerations I'm using on a regular basis. I'd be using something like this:

SELECT pg_type.typname AS enum_type, pg_enum.enumlabel AS enmu_label FROM 
pg_type JOIN pg_enum ON pg_enum.enumtypid = pg_type.oid;

or

SELECT distinct pg_type.typname AS enum_type FROM pg_type JOIN pg_enum ON 
pg_enum.enumtypid = pg_type.oid;

Is this bad practice?

Answer 1

Is this bad practice?

No, not at all, modifying the catalog is bad practice but there is no reason not to query it.

But in your query…

SELECT distinct pg_type.typname AS enum_type FROM pg_type JOIN pg_enum ON pg_enum.enumtypid = pg_type.oid;

…there isn't any need to join pg_enum and use distinct:

create type mood as enum ('sad', 'ok', 'happy');

select * from pg_enum;

enumtypid | enumsortorder | enumlabel
:-------- | :------------ | :--------
53430     | 1             | sad      
53430     | 2             | ok       
53430     | 3             | happy    

select typname from pg_type where typtype='e';

| typname |
| :------ |
| mood    |

dbfiddle here

Answer 2

What @Jack said. Plus, if all you need is the list of registered values for an enum type, there are some Enum Support Functions to do that. Based on Jack's example:

SELECT enum_range(null::mood);

enum_range
--------------
{sad,ok,happy}

That's simpler and resilient against (unlikely) changes in future major Postgres versions that might break your query.

dbfiddle here