Provide data type mapping for catalog types

[dvarrazzo]

Several types found in pg_catalog are not mapped to Python types.

We should introduce a psycopg.types.catalog module implementing mappings:

• oid: uint32 (already implemented in psycopg.types.numeric).
• cid: uint32
• int2vector: similar to smallint[], with space-separated text representation, 0-based array binary representation.
• oidvector: similar to int[], see int2vector
• tid: pair (block, offset) (uint32, uint16)
• xid: uint32
• xid8: uint64
• pg_lsn: uint64

This query gives an overview of where the types are used:

select a.atttypid::regtype, relname, attname from pg_attribute a join pg_class c on a.attrelid = c.oid join pg_namespace s on s.oid = c.relnamespace where nspname = 'pg_catalog' order by a.atttypid::regtype::text, relname, attname;

[bbibenyo-spiria]

Would these Python types be subclasses of Generic[T]/Dumper or are we simply adding a dictionary mapping of Postgres to Python types?

[dvarrazzo]

I'm taking a look at these types now. Looking at cid, AFAICS there are no other operators - cid can only be compared with cid.

piro=# select oprleft::regtype, oprname, oprright::regtype from pg_operator
    where oprleft = 'cid'::regtype or oprright = 'cid'::regtype;
┌─────────┬─────────┬──────────┐
│ oprleft │ oprname │ oprright │
├─────────┼─────────┼──────────┤
│ cid     │ =       │ cid      │
└─────────┴─────────┴──────────┘
(1 row)

this means that, if we dump an object to a cid (for instance querying select * from pg_class where cmin = %s) then we cannot dump the type as a number: it must be either unknown or cid.

The model I had in mind was the same of oid, but oids have more casts and operators to support mixing with numbers.

If this is the case, if loading a cid returns a Python integer, then loading it back we would need a Cid wrapper. The Oid doesn't normally need such wrapper.

Uhm... I'm questioning if this would be useful at all, or for every type, or in both directions...

[itsankitkp]

hi @dvarrazzo can you give little more information about what is expected/desired and where do we have a reference implementation for this? Thanks