Re: Design database

Thanks you !
So I’ve implemented your solution Despesz, but I have an upsert function throwing an error : publication (parent table) has no item, even id I’ve added a "SET CONSTRAINTS ALL DEFERRED;
The postgresql version is 9.3; that's why I can not use upsert do on conflict.

CREATE OR REPLACE FUNCTION upsert_related_publications_v1(
in_related_publications_id INTEGER,
in_cms_title TEXT,
in_title TEXT,
in_related_publications_items JSON
)
RETURNS TABLE (
out_related_publications_id INTEGER
) AS $$
DECLARE
inserted_related_publications_id INTEGER;
BEGIN
SET CONSTRAINTS ALL DEFERRED;
-- Firstly, an upsert is performed for the related_publications table.
WITH upsert AS (
UPDATE related_publications
SET
cms_title = in_cms_title,
title = in_title
WHERE related_publications_id = in_related_publications_id
RETURNING related_publications_id
)
INSERT INTO related_publications (cms_title, title)
SELECT
in_cms_title,
in_title
WHERE NOT EXISTS (
SELECT related_publications_id FROM upsert
) RETURNING related_publications_id INTO inserted_related_publications_id;

-- Then, all related publications items that are not handled by the related JSON are
-- considered as to be dropped.
WITH related_publications_item_record AS (
SELECT
related_publications_item_id
FROM json_populate_recordset(NULL::related_publications_item, in_related_publications_items)
)
DELETE FROM related_publications_item
WHERE
related_publications_item.related_publications_item_id NOT IN (
SELECT coalesce(related_publications_item_record.related_publications_item_id, -1)
FROM related_publications_item_record
)
AND related_publications_item.related_publications_id = coalesce(inserted_related_publications_id, in_related_publications_id);

-- Finally, related publications items are upserted.
WITH related_publications_item_record AS (
SELECT
related_publications_item_id,
content_id,
item_order
FROM json_populate_recordset(NULL::related_publications_item, in_related_publications_items)
)
UPDATE related_publications_item
SET
content_id = related_publications_item_record.content_id,
item_order = related_publications_item_record.item_order
FROM related_publications_item_record
WHERE related_publications_item.related_publications_item_id = related_publications_item_record.related_publications_item_id;

WITH related_publications_item_record AS (
SELECT
related_publications_item_id,
content_id,
item_order
FROM json_populate_recordset(NULL::related_publications_item, in_related_publications_items)
)
INSERT INTO related_publications_item (related_publications_id, content_id, item_order)
SELECT
coalesce(inserted_related_publications_id, in_related_publications_id),
related_publications_item_record.content_id,
related_publications_item_record.item_order
FROM related_publications_item_record
WHERE related_publications_item_record.related_publications_item_id IS NULL;

RETURN QUERY SELECT coalesce(inserted_related_publications_id, in_related_publications_id);
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

Thanks a lot

> Le 3 févr. 2021 à 17:44, hubert depesz lubaczewski <depesz(at)depesz(dot)com> a écrit :
>
> On Wed, Feb 03, 2021 at 08:35:41AM -0700, David G. Johnston wrote:
>> On Wed, Feb 3, 2021 at 8:23 AM Mai Peng <[1]maily(dot)peng(at)webedia-group(dot)com> wrote:
>>
>> Hello,
>>
>> I’ve got a table name publication, and another table named publication_item.
>> Each publication_item is linked to a publication by publication_id.
>> How could I add a constraint that check each publication has one or more publication_item when a tuple is inserted ?
>> I don’t want to store items in the same table as publication because we could have 1-> n items.
>>
>> [2]https://www.postgresql.org/docs/current/tutorial-fk.html
>
> I don't think it helps. Fkey can check that publication_item contains
> valid publication_id, but doesn't ensure that every publication has at
> least one item.
>
> As for the problem of OP, I think this describes working solution:
> https://www.depesz.com/2017/07/03/how-to-make-sure-there-is-always-at-least-one-sub-record/
>
> Best regards,
>
> depesz
>