Find all composite type component types using WITH RECURSIVE

Question

Given the typname of a composite type, how do I find the type oids of all component types recursively?

Example:

CREATE TYPE t_station AS (x INT,
                          y INT,
                          label VARCHAR);

CREATE TYPE t_address AS (city VARCHAR,
                          street VARCHAR,
                          no INT,
                          stations t_station[]);

CREATE TYPE t_employee AS (name VARCHAR,
                           age INT,
                           coins INT[],
                           notes VARCHAR,
                           address t_address);

I can get the type oids of the members of t_employee:

SELECT
   t.typname, t.oid, a.attname, a.atttypid
FROM
   pg_attribute a INNER JOIN pg_type t ON a.attrelid = t.typrelid
   AND t.typname = 't_employee'

But I need to recurse that, which I guess can be done using WITH RECURSIVE:

WITH RECURSIVE allattrs(typname, oid, attname, atttypid) AS (
  select t.typname, t.oid, a.attname, a.atttypid from pg_attribute a inner join pg_type t on a.attrelid = t.typrelid and t.typname = 't_employee'
  union all
  select z.* from
  (select t.typname, t.oid, a.attname, a.atttypid from pg_attribute a inner join pg_type t on a.attrelid = t.typrelid) z,
  allattrs y where y.atttypid = z.oid
)
SELECT * FROM allattrs limit 100
;

But that does not find the inner array of t_station composite type.

Answer 1

Array types break the simple chain you are following. In case of an array type you have to resolve pg_type.typelem to get to the base type.

WITH RECURSIVE cte(typname, type_oid, attname, atttypid, typelem) AS (
   SELECT t.typname, t.oid, a.attname, a.atttypid, t.typelem
   FROM   pg_type t
   LEFT   JOIN pg_attribute a ON  a.attrelid = t.typrelid
                              AND a.attnum > 0
                              AND NOT a.attisdropped
   WHERE  t.typrelid = 't_employee'::regclass

   UNION ALL
   SELECT t.typname, t.oid
         ,COALESCE(a.attname, t.typelem::regtype::text)
         ,COALESCE(a.atttypid, t.typelem), t.typelem
   FROM   cte c
   JOIN   pg_type t ON t.oid = c.atttypid AND (t.typtype = 'c' OR t.typelem > 0)
   LEFT   JOIN pg_attribute a ON  a.attrelid = t.typrelid
                              AND a.attnum > 0
                              AND NOT a.attisdropped
   )
SELECT typname, type_oid, attname, atttypid
FROM   cte
WHERE  typelem = 0  -- filter out rows for array types

If you want to include extra rows for array types in the result, remove the final WHERE condition ..

This JOIN condition only follows composite types or arrays:

AND (t.typtype = 'c' OR t.typelem > 0)

I also added conditions to exclude system columns and dead columns:

AND a.attnum > 0
AND NOT a.attisdropped

Details about catalog tables in the manual.