postgres=# create domain my_text as text;
CREATE DOMAIN
postgres=# alter domain my_text add constraint max_len check (length(value) <= 30);
ALTER DOMAIN
postgres=# create table t (code my_text);
CREATE TABLE
postgres=# create view v as select * from t;
CREATE VIEW
postgres=# insert into t values ('a'),('b');
INSERT 0 2
postgres=# begin; alter domain my_text drop constraint max_len; alter domain my_text add constraint max_len check (length(value) <= 3); commit;
BEGIN
ALTER DOMAIN
ALTER DOMAIN
COMMIT
postgres=# insert into t values ('1234');
ERROR:  value for domain my_text violates check constraint "max_len"
postgres=# select * from v;
 code 
------
 a
 b
(2 rows)