Re: Foreign keys question (performance) - Mailing list pgsql-general

-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org] On Behalf Of Phoenix Kiula
Sent: Tuesday, December 06, 2011 11:46 AM
To: Alban Hertroys
Cc: PG-General Mailing List
Subject: Re: [GENERAL] Foreign keys question (performance)

On Sun, Dec 4, 2011 at 7:41 PM, Phoenix Kiula <phoenix.kiula@gmail.com>
wrote:
> On Sun, Dec 4, 2011 at 7:14 PM, Alban Hertroys <haramrae@gmail.com> wrote:
>> On 4 Dec 2011, at 11:19, Phoenix Kiula wrote:
> ....
>
>>
>> INSERTs in the parent table don't need to check for any reference from
the child table, since they're new; there can't be a reference. UPDATEs and
DELETEs do though, whether you let them CASCADE or not. If you don't, then
the database raises a foreign key constraint violation. If you do, then it
needs to modify the relevant rows in the child table.
>>
>> Likewise, INSERTs and UPDATEs in the child table need to verify that - if
their reference key changed - they're still referencing a valid row.




I have a problem.

Here's my table designs. The problem is that if Table 1 (stores) has a
foreign key reference from another child table (stores_registered), then
when I update Table 1, it throws an error that referential intergrity is
being violate because Table 2 depends on Table 1.
However, if I update Table 2 first, it tells me  that the fkey in Table 1
doesn't exist (of course).

Any ideas? What am I missing? How do updates work in terms of CASCADE?

Thanks!





mydb=# \d stores



                              Table "public.stores"
     Column      |            Type             |            Modifiers
-----------------+-----------------------------+------------------------
-----------------+-----------------------------+---------
 strid           | character varying(35)       | not null
 plc             | text                        | not null
 user_registered | boolean                     |
 private_key     | character varying(6)        | default NULL::character
varying
 modify_date     | timestamp without time zone | default now()
 ip              | bigint                      |
 plc_md5         | text                        |
Indexes:
    "idx_stores_pkey" PRIMARY KEY, btree (strid)
    "idx_stores_ip_plc" UNIQUE, btree (ip, plc_md5)
    "idx_stores_modify_date" btree (modify_date)
    "idx_stores_plcmd5" btree (plc_md5)
Check constraints:
    "stores_strid_check" CHECK (strid::text ~ '[-.~a-z0-9_]'::text)
Referenced by:
    TABLE "stores_registered" CONSTRAINT "fk_stores_registered"
FOREIGN KEY (strid) REFERENCES stores(strid) MATCH FULL ON UPDATE CASCADE ON
DELETE CASCADE
    TABLE "stores_stats" CONSTRAINT "fk_stats" FOREIGN KEY (strid)
REFERENCES stores(strid) ON DELETE CASCADE
    TABLE "interesting" CONSTRAINT "interesting_strid_fkey" FOREIGN KEY
(strid) REFERENCES stores(strid) MATCH FULL ON UPDATE CASCADE ON DELETE
CASCADE




mydb=# \d stores_registered





    Column    |            Type             |            Modifiers
--------------+-----------------------------+---------------------------
--------------+-----------------------------+------
 strid        | character varying(35)       | not null
 plc          | text                        | not null
 user_id      | character varying(30)       | not null
 modify_date  | timestamp without time zone | default now()
 plc_md5      | text                        |
Indexes:
    "idx_stores_registered_pkey" PRIMARY KEY, btree (strid)
    "idx_stores_registered_userid_plc" UNIQUE, btree (user_id, plc_md5)
Check constraints:
    "stores_strid_check" CHECK (strid::text ~ '[-.~a-z0-9_]'::text)
    "stores_plc_check" CHECK (plc <> ''::text) Foreign-key constraints:
    "fk_stores_registered" FOREIGN KEY (strid) REFERENCES
stores(strid) MATCH FULL ON UPDATE CASCADE ON DELETE CASCADE
    "stores_registered_users_fkey" FOREIGN KEY (user_id) REFERENCES
users(id) MATCH FULL ON DELETE CASCADE

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If I am reading this right your issue is not "stores_registered" but
"stores_stats" - the later is missing the "ON UPDATE CASCADE" modifier to
its foreign key.

With "ON UPDATE CASCADE" when you change the primary key all related foreign
keys have their values changed as well.  With this enabled you do not need
to directly modify "table2" but instead you let the system do its thing when
you update "table1".  I believe you have the logic figured out but in this
case (and maybe the error message is simply unclear - you never did provide
your UPDATE statement nor your error message) I think it is the missing ON
UPDATE CASCADE on "stores_stats" that is your issue.

David J.