Re: Forward declaration of table - Mailing list pgsql-general

On 08/23/2016 10:10 AM, Alexander Farber wrote:
> Good evening,
>
> with PostgreSQL 9.5.3 I am using the following table to store 2-player
> games:
>
>     DROP TABLE IF EXISTS words_games;
>     CREATE TABLE words_games (
>             gid SERIAL PRIMARY KEY,
>             created timestamptz NOT NULL,
>             player1 integer REFERENCES words_users(uid) ON DELETE
>     CASCADE NOT NULL,
>             player2 integer REFERENCES words_users(uid) ON DELETE CASCADE,
>             played1 timestamptz,
>             played2 timestamptz,
>             -- mid1 integer REFERENCES words_moves(mid) ON DELETE CASCADE,
>             -- mid2 integer REFERENCES words_moves(mid) ON DELETE CASCADE,
>             score1 integer NOT NULL CHECK(score1 >= 0),
>             score2 integer NOT NULL CHECK(score2 >= 0),
>             hand1 varchar[7] NOT NULL,
>             hand2 varchar[7] NOT NULL,
>             pile  varchar[116] NOT NULL,
>             letters varchar[15][15] NOT NULL,
>             values integer[15][15] NOT NULL,
>             bid integer NOT NULL REFERENCES words_boards ON DELETE CASCADE
>     );
>
>
> This has worked well for me (when a user connects to the game server, I
> send her all games she is taking part in), but then I have decided to
> add another table to act as a "logging journal" for player moves:
>
> DROP TABLE IF EXISTS words_moves;
>
> DROP TYPE IF EXISTS words_action;
>
> CREATE TABLE words_moves (
>         mid SERIAL PRIMARY KEY,
>         action words_action NOT NULL,
>         gid integer NOT NULL REFERENCES words_games ON DELETE CASCADE,
>         uid integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
>         played timestamptz NOT NULL,
>         tiles jsonb,
>         score integer CHECK(score > 0)
> );
>
> Also, in the former table words_games I wanted to add references to the
> latest moves performed by players:
>
>         -- mid1 integer REFERENCES words_moves(mid) ON DELETE CASCADE,
>         -- mid2 integer REFERENCES words_moves(mid) ON DELETE CASCADE,
>
> The intention is: whenever a player connects to the server, sent her all
> active games and status updates on the recent opponent moves.
>
> However the 2 added columns do not work:
>
>     ERROR:  relation "words_moves" does not exist
>     ERROR:  relation "words_games" does not exist
>     ERROR:  relation "words_moves" does not exist
>
>
> So my question is if I can somehow "forward declare" the words_moves table?

Off the top of my head:

Change this:
--mid1 integer REFERENCES words_moves(mid) ON DELETE CASCADE,
--mid2 integer REFERENCES words_moves(mid) ON DELETE CASCADE,

to

mid1 integer
mid2 integer

and then after

CREATE TABLE words_moves ...

use ALTER TABLE ADD table_constraint :

https://www.postgresql.org/docs/9.5/static/sql-altertable.html

to add the FK references to word_games.

>
> Here are all tables of my game for more context:
> https://gist.github.com/afarber/c40b9fc5447335db7d24
>
> Thank you
> Alex
>


--
Adrian Klaver
adrian.klaver@aklaver.com