Hello hackers,
Currently obtaining the base type of a domain involves a somewhat long
recursive query. Consider:
```
create domain mytext as text;
create domain mytext_child_1 as mytext;
create domain mytext_child_2 as mytext_child_1;
```
To get `mytext_child_2` base type we can do:
```
WITH RECURSIVE
recurse AS (
SELECT
oid,
typbasetype,
COALESCE(NULLIF(typbasetype, 0), oid) AS base
FROM pg_type
UNION
SELECT
t.oid,
b.typbasetype,
COALESCE(NULLIF(b.typbasetype, 0), b.oid) AS base
FROM recurse t
JOIN pg_type b ON t.typbasetype = b.oid
)
SELECT
oid::regtype,
base::regtype
FROM recurse
WHERE typbasetype = 0 and oid = 'mytext_child_2'::regtype;
oid | base
----------------+------
mytext_child_2 | text
```
Core has the `getBaseType` function, which already gets a domain base type
recursively.
I've attached a patch that exposes a `pg_basetype` SQL function that uses
`getBaseType`, so the long query above just becomes:
```
select pg_basetype('mytext_child_2'::regtype);
pg_basetype
-------------
text
(1 row)
```
Tests and docs are added.
Best regards,
Steve Chavez
From 9be553c2a3896c12d959bc722a808589765f3db0 Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavez...@gmail.com>
Date: Sat, 9 Sep 2023 00:58:44 -0300
Subject: [PATCH] Add pg_basetype(regtype)
Currently obtaining the base type of a domain involves a long SQL query,
this specially in the case of recursive domain types.
To solve this, use the already available getBaseType() function,
and expose it as the pg_basetype SQL function.
---
doc/src/sgml/func.sgml | 25 +++++++++++++++++++
src/backend/utils/adt/misc.c | 14 +++++++++++
src/include/catalog/pg_proc.dat | 3 +++
src/test/regress/expected/domain.out | 36 ++++++++++++++++++++++++++++
src/test/regress/sql/domain.sql | 17 +++++++++++++
5 files changed, 95 insertions(+)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 24ad87f910..69393ca557 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -24723,6 +24723,31 @@ SELECT typlen FROM pg_type WHERE oid = pg_typeof(33);
</para></entry>
</row>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_basetype</primary>
+ </indexterm>
+ <function>pg_basetype</function> ( <parameter>type</parameter> <type>oid</type> )
+ <returnvalue>regtype</returnvalue>
+ </para>
+ <para>
+ Returns the OID of the base type of a domain or if the argument is a basetype it returns the same type.
+ If there's a chain of domain dependencies, it will recurse until finding the base type.
+ </para>
+ <para>
+ For example:
+<programlisting>
+CREATE DOMAIN mytext as text;
+
+SELECT pg_basetype('mytext'::regtype);
+ pg_typeof
+-----------
+ text
+</programlisting>
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index 5d78d6dc06..c0c3c9e98b 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -43,6 +43,7 @@
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
+#include "utils/syscache.h"
#include "utils/lsyscache.h"
#include "utils/ruleutils.h"
#include "utils/timestamp.h"
@@ -566,6 +567,19 @@ pg_typeof(PG_FUNCTION_ARGS)
PG_RETURN_OID(get_fn_expr_argtype(fcinfo->flinfo, 0));
}
+/*
+ * Return the base type of the argument.
+ */
+Datum
+pg_basetype(PG_FUNCTION_ARGS)
+{
+ Oid oid = PG_GETARG_OID(0);
+
+ if (!SearchSysCacheExists1(TYPEOID, ObjectIdGetDatum(oid)))
+ PG_RETURN_NULL();
+
+ PG_RETURN_OID(getBaseType(oid));
+}
/*
* Implementation of the COLLATE FOR expression; returns the collation
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 9805bc6118..f19bf47242 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3874,6 +3874,9 @@
{ oid => '1619', descr => 'type of the argument',
proname => 'pg_typeof', proisstrict => 'f', provolatile => 's',
prorettype => 'regtype', proargtypes => 'any', prosrc => 'pg_typeof' },
+{ oid => '6312', descr => 'get the base type of a domain',
+ proname => 'pg_basetype', proisstrict => 'f', provolatile => 's',
+ prorettype => 'regtype', proargtypes => 'oid', prosrc => 'pg_basetype' },
{ oid => '3162',
descr => 'collation of the argument; implementation of the COLLATION FOR expression',
proname => 'pg_collation_for', proisstrict => 'f', provolatile => 's',
diff --git a/src/test/regress/expected/domain.out b/src/test/regress/expected/domain.out
index 6d94e84414..4f0253cd71 100644
--- a/src/test/regress/expected/domain.out
+++ b/src/test/regress/expected/domain.out
@@ -1207,3 +1207,39 @@ create domain testdomain1 as int constraint unsigned check (value > 0);
alter domain testdomain1 rename constraint unsigned to unsigned_foo;
alter domain testdomain1 drop constraint unsigned_foo;
drop domain testdomain1;
+--
+-- Get the base type of a domain
+--
+create domain mytext as text;
+create domain mytext_child_1 as mytext;
+create domain mytext_child_2 as mytext_child_1;
+select pg_basetype('mytext'::regtype);
+ pg_basetype
+-------------
+ text
+(1 row)
+
+-- gets base types recursively
+select pg_basetype('mytext_child_1'::regtype);
+ pg_basetype
+-------------
+ text
+(1 row)
+
+select pg_basetype('mytext_child_2'::regtype);
+ pg_basetype
+-------------
+ text
+(1 row)
+
+-- if already a base type, get the same
+select pg_basetype('text'::regtype);
+ pg_basetype
+-------------
+ text
+(1 row)
+
+drop domain mytext cascade;
+NOTICE: drop cascades to 2 other objects
+DETAIL: drop cascades to type mytext_child_1
+drop cascades to type mytext_child_2
diff --git a/src/test/regress/sql/domain.sql b/src/test/regress/sql/domain.sql
index 745f5d5fd2..3c824da03a 100644
--- a/src/test/regress/sql/domain.sql
+++ b/src/test/regress/sql/domain.sql
@@ -809,3 +809,20 @@ create domain testdomain1 as int constraint unsigned check (value > 0);
alter domain testdomain1 rename constraint unsigned to unsigned_foo;
alter domain testdomain1 drop constraint unsigned_foo;
drop domain testdomain1;
+
+--
+-- Get the base type of a domain
+--
+
+create domain mytext as text;
+create domain mytext_child_1 as mytext;
+create domain mytext_child_2 as mytext_child_1;
+
+select pg_basetype('mytext'::regtype);
+-- gets base types recursively
+select pg_basetype('mytext_child_1'::regtype);
+select pg_basetype('mytext_child_2'::regtype);
+-- if already a base type, get the same
+select pg_basetype('text'::regtype);
+
+drop domain mytext cascade;
--
2.34.1
