insert/update/delete触发器如何使用相同的触发器函数避免新旧对象的问题

Question

我正在寻找解决这种情况的优雅方法：

我创建了一个触发器函数，每当在 warehouse_supplies.[=35= 上插入或更新行时，它会使用一些详细信息行的总和来更新 table supply ]
PostgreSQL insert or update 语法允许我为插入和更新条件共享相同的函数 sync_supply_stock()。
然而，当我尝试将 after delete 条件连接到函数时，它不能被重用（尽管它在逻辑上是有效的），因为返回的对象必须是 old 而不是 new.

-- The function I want to use for the 3 conditions (insert, update, delete)
create or replace function sync_supply_stock ()
returns trigger
as $$
begin
    -- update the supply whose stock just changed in warehouse_supply with
    -- the sum its stocks on all the warehouses.
    update supply 
    set stock = (select sum(stock) from warehouse_supplies where supply_id = new.supply_id)
    where supply_id = new.supply_id;
    
    return new;
end;
$$ language plpgsql;

-- The (probably) unnecessary copy of the previous function, this time returning old.
create or replace function sync_supply_stock2 ()
returns trigger
as $$
begin
    -- update the supply whose stock just changed in warehouse_supply with
    -- the sum its stocks on all the warehouses.
    update supply 
    set stock = (select sum(stock) from warehouse_supplies where supply_id = old.supply_id)
    where supply_id = old.supply_id;
    
    return old;
end;
$$ language plpgsql;

-- The after insert/update trigger
create trigger on_warehouse_supplies__after_upsert after insert or update
on warehouse_supplies for each row 
execute procedure sync_supply_stock ();

-- The after delete trigger
create trigger on_warehouse_supplies__after_delete after delete
on warehouse_supplies for each row 
execute procedure sync_supply_stock2 ();

我是不是遗漏了什么或者是否有任何修复方法可以将 sync_supply_stock2() 复制为 sync_supply_stock2()？

编辑

为了未来读者的利益，根据@bergi 的回答和讨论，这是一个可能的分解解决方案

create or replace function sync_supply_stock ()
returns trigger
as $$
declare
    _supply_id int;
begin
    -- read the supply_id column from `new` on insert/update conditions and from `old` on delete conditions
    _supply_id = coalesce(new.supply_id, old.supply_id);
    
    -- update the supply whose stock just changed in of_warehouse_supply with
    -- the sum its stocks on all the warehouses.
    update of_supply 
    set stock = (select sum(stock) from of_warehouse_supplies where supply_id = _supply_id)
    where supply_id = _supply_id;
            
    -- returns `new` on insert/update conditions and `old` on delete conditions 
    return coalesce(new, old);
end;
$$ language plpgsql;

create trigger on_warehouse_supplies__after_upsert after insert or update
on of_warehouse_supplies for each row 
execute procedure sync_supply_stock ();

create trigger on_warehouse_supplies__after_delete after delete
on of_warehouse_supplies for each row 
execute procedure sync_supply_stock ();

Answer 1

for the returning object must be old instead of new.

没有。 return 值仅与 BEFORE ROW 或 INSTEAD OF 触发器相关。来自 the docs：“触发 row-level 触发器的 return 值 AFTER 或触发 statement-level 触发器 BEFORE 或 AFTER 总是被忽略；它也可能是 null".

因此您只需创建 sync_supply_stock 触发器函数 RETURN NULL 即可用于所有操作。

insert/update/delete触发器如何使用相同的触发器函数避免新旧对象的问题

How to use the same trigger function for insert/update/delete triggers avoiding the problem with new and old objects

postgresql

postgresql-triggers

postgresql-12