问题描述
我在数据库中有一个用户应该能够订购的列表.
I have a list in a database that the user should be able to order.
itemname| order value (int)
--------+---------------------
salad | 1
mango | 2
orange | 3
apples | 4
从数据库加载时，我只是按 order_value 排序.
On load from the database, I simply order by order_value.
通过拖放，他应该能够移动apples，使其出现在列表顶部..
By drag 'n drop, he should be able to move apples so that it appears at the top of the list..
itemname| order value (int)
--------+---------------------
apples | 4
salad | 1
mango | 2
orange | 3
好的.所以现在在内部我必须更新每个列表项！如果列表有 20 或 100 个项目，那么对于简单的拖动操作来说就需要很多更新.
Ok. So now internally I have to update EVERY LIST ITEM! If the list has 20 or 100 items, that's a lot of updates for a simple drag operation.
itemname| order value (int)
--------+---------------------
apples | 1
salad | 2
mango | 3
orange | 4
我宁愿只更新一次.我想到的一种方法是内部订单"是否是 double 值.
I'd rather do it with only one update. One way I thought of is if "internal Order" is a double value.
itemname| order value (double)
--------+---------------------
salad | 1.0
mango | 2.0
orange | 3.0
apples | 4.0
所以在拖放操作之后，我指定 apples 的值小于它要出现在前面的项目:
SO after the drag n' drop operation, I assign apples has a value that is less than the item it is to appear in front of:
itemname| order value (double)
--------+---------------------
apples | 0.5
salad | 1.0
mango | 2.0
orange | 3.0
.. 如果一个项目被拖到中间某处，它的 order_value 比它之后出现的那个大.. 这里我将 orange 移动到 <代码>沙拉和芒果:
.. and if an item is dragged into the middle somewhere, its order_value is bigger than the one it appears after .. here I moved orange to be between salad and mango:
itemname| order value (double)
--------+---------------------
apples | 0.5
salad | 1.0
orange | 1.5
mango | 2.0
对更好的方法有什么想法吗?
Any thoughts on better ways to do this?
推荐答案
我最终使用了一个 邻接表.我当时并不知道.
I ended up using an adjacencies table. I didn't know about it at the time.
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