postgresql: enum and character varying, updating

Question

I have the ENUM type in postgresql

CREATE TYPE user_state AS ENUM (\'unconfirmed\', \'locked\', \'active\');
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Answer 1

Alternatively you may register equal operator instead of define cast one. I did it for Java + MyBatis in similar situation:

CREATE FUNCTION type_user_state_with_text_equals(_a user_state, _b text)
    RETURNS boolean AS
    $func$
        SELECT _a = _b::user_state;
    $func$
    LANGUAGE SQL IMMUTABLE STRICT;

CREATE OPERATOR = (
    leftarg = user_state,
    rightarg = text,
    procedure = type_user_state_with_text_equals,
    COMMUTATOR = =,
    NEGATOR = !=,
    HASHES, MERGES
);

You may read about postgres user-defined operations in documentation and do not forget look at optimization hints.

Answer 2

The problem with a simple attempt is you have a cast calling the cast, calling the cast, calling the cast...

You need somehow to get away from varchar->enum in your cast. Simplest (most understandable) way is to just manually convert. Note the string literals being cast in the case statement aren't text they are quoted-unknown-type which sidesteps the infinite recursion.

BEGIN;

CREATE TYPE t_tl AS ENUM ('red', 'amber', 'green');

CREATE FUNCTION dummy_cast(varchar) RETURNS t_tl AS $$
    SELECT CASE $1
        WHEN 'red' THEN 'red'::t_tl
        WHEN 'amber' THEN 'amber'::t_tl
        WHEN 'green' THEN 'green'::t_tl
    END;
$$ LANGUAGE SQL;

CREATE CAST (varchar AS t_tl) WITH FUNCTION dummy_cast(varchar) AS ASSIGNMENT;

CREATE TABLE t (x t_tl);

INSERT INTO t VALUES ('red');
INSERT INTO t VALUES ('green'::varchar);

SELECT * FROM t;

ROLLBACK;

Answer 3

Very late to the party here, but I would like to add that in this specific case it is enough to simply cast the varchar to text to prevent recursion.

CREATE FUNCTION dummy_cast(varchar) RETURNS t_tl AS $$
    SELECT ('' || $1)::t_tl;
$$ LANGUAGE SQL;