Reordering items in a RESTful way

Question

I have a table that has the following data:

id position name
== ======== =========
1     4      Fred
2     2      Wilma
3     1      Pebbles
4     5      Barney
         


        

Answer 1

In order to do it efficiently use a hash table and never reorder everything just put them in between by changing their index key. What do I mean?

Lets say

1 a
2 b
3 c
4 d
5 e

PUT /user/1/reorder/2

Inside I would do, also the position is derived from the position in your index

1  2   b
2  2.5 a
3  3   c
4  4   d
5  5 e

As noted by Kajow, this approach has two issues:

• After multiple reorders, float numbers might not suffice

• Float number precision

To solve them:

• We don't use floats but big numbers 100000,200000,300000 etc and reorder, 200000,250000,30000,etc.

• After x number of reorders we reset to 100000,200000,300000,400000. There might be a way to reorder only small parts every x divisions in order to keep this process simple, small and sporadic