How to sort the product list and support spreading operations by dragging?

Drag and drop ordering and spread page operation on e-commerce platform product list

Many e-commerce applications need to support users to drag and drop to adjust the order of product lists and allow spread-page operations. This article introduces an efficient sorting algorithm that implements this function while minimizing changes to existing systems (such as product addition and modification operations). The database already has a sort field (the initial value is 0), and the product list is currently displayed in reverse order of time.

Sorting algorithm design

We use a sort field-based algorithm. During initial sorting, you need to assign a value to sort field of each item and reserve a sufficient gap, such as 1000. The following SQL statements implement initial sorting:

 SET @sort := 0;
UPDATE product SET sort = (@sort := @sort 1000) ORDER BY id;

This will cause sort value to start at 1000, incrementing by 1000 each time. For example:

id	sort
1	1000
2	2000
3	3000

When the user drags the product, the new sort value is recalculated. Suppose that the item with id 3 is dragged between id 1 and id 2, and the new sort value is the intermediate value of the two sort values ​​before and after:

New sort value = 1000 (2000 - 1000) / 2 = 1500

Update the sort value of the product with id 3:

id	sort
1	1000
3	1500
2	2000

To improve flexibility, random numbers can be added when calculating intermediate values ​​to avoid too uniform sort values.

When sort value gap is not enough to support finer sorting, readjust sort value and expand the gap:

 SET @sort := 0;
UPDATE product SET sort = (@sort := @sort 1000) ORDER BY sort;

This algorithm ensures that the sorting function is continuously efficient and has minimal impact on existing systems. The spread page operation only needs to correctly obtain sort value of the target position during the drag and drop process, and the algorithm itself does not need to be modified.

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