# Fast way of finding new position for model object?

**URL:** <https://www.ruby-forum.com/t/fast-way-of-finding-new-position-for-model-object/56784>\
**Category:** Rails\
**Created:** [April 3, 2006, 11:40pm UTC](https://www.ruby-forum.com/t/fast-way-of-finding-new-position-for-model-object/56784 "2006-04-03T23:40:10Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![ryana](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ea5d25/32.png) [@ryana](https://www.ruby-forum.com/u/ryana)\
**Post date:** [April 3, 2006, 11:40pm UTC](https://www.ruby-forum.com/t/fast-way-of-finding-new-position-for-model-object/56784/1 "2006-04-03T23:40:10Z")

</div>

I have a model object that acts as a list. The position of each object  
is determined by two factors: number of votes ascending and age of  
object descending. When a user adds or deletes a vote I need to  
quickly update the associated model object’s position. Right now this  
is done with the following method:

def update\_position  
position = nil

```
Bug.find(:all, :order => "votes_count DESC, id

```

ASC").each\_with\_index{ |bug,i|  
if bug.id == self.id  
position = i  
break  
end  
}

```
self.insert_at(position)

```

end

Basically, find all of the bugs in the order in which they’re wanted  
and then iterate through each until the new position of this bug is  
found. When it’s found, save the position, break out of the loop and  
insert the current model into the correct position.

Unfortunately, this method is rather slow. I broke the  
Bug.find().each\_with\_index() line into two separate lines so that I  
could easily benchmark the method and see what was sucking up all of  
my time. Here are the results:

```
                 user system total real

```

find\_all 1.250000 0.030000 1.280000 ( 1.308910)  
each\_with\_index 0.070000 0.000000 0.070000 ( 0.076316)

The find\_all can take anywhere from 1.1 - 2.3 seconds on a table with  
2000 rows, in my experiments.

Is there a more efficient way to determine the new position of a row?  
I had hoped there was some magical sql query I could use like `SELECT POSITION(*) FROM bugs WHERE id = #{bug.id}` that would spit out  
correct position in one quick call. Or that I could find the rows  
around a specific record when they’re sorted in the order I need.  
Those both seem to be pipe dreams, however.

Anyone have any suggestions as to how I can quickly find the new  
position of an object in a list, with my given sorting criteria?

–  
Ryan

---

<div class="post-metadata">

**Author:** ![ryana](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ea5d25/32.png) [@ryana](https://www.ruby-forum.com/u/ryana)\
**Post date:** [April 4, 2006, 12:44am UTC](https://www.ruby-forum.com/t/fast-way-of-finding-new-position-for-model-object/56784/2 "2006-04-04T00:44:46Z")

</div>

can i ask why you need to treat this as a list? what are you using  
position  
for?

---

<div class="post-metadata">

**Author:** ![ryana](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ea5d25/32.png) [@ryana](https://www.ruby-forum.com/u/ryana)\
**Post date:** [April 4, 2006, 12:57am UTC](https://www.ruby-forum.com/t/fast-way-of-finding-new-position-for-model-object/56784/3 "2006-04-04T00:57:10Z")

</div>

The position column is basically a cache of the bug’s ranking. Having  
this model act as a list let’s me slice and filter the objects while  
still being able to quickly retrieve and display each object’s ranking  
in the overall list.

–  
Ryan