0

我正在寻找一种优雅的解决方案来解决这种情况：

  • 我创建了一个触发器函数supply，每当在warehouse_supplies.
  • PostgreSQLinsert or update语法允许我sync_supply_stock()为插入和更新条件共享相同的函数。
  • 但是，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 ();

我是否遗漏了什么，或者是否有任何修复复制sync_supply_stock2()为的方法sync_supply_stock2()？

编辑

为了未来读者的利益，遵循@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 ();
4

1 回答 1

2

对于返回的对象必须是old而不是new.

不，返回值仅与BEFORE ROW或INSTEAD OF触发器相关。来自文档：“触发的行级触发器AFTER或触发的语句级触发器的返回值BEFORE或AFTER总是被忽略；它也可能是 null ”。

所以你可以只做你的sync_supply_stock触发功能RETURN NULL，它可以用于所有操作。

于 2020-08-08T14:34:51.720 回答