ActiveRecord - default ID vs custom identifier

Hi,

So far I’ve let Rails and ActiveRecord rule the game. But I think
there’s some things I should change.

I have a record (called Tag) that is searched by using the default auto
incrementable Id that AR provides. On the Tag record I also keep a
unique identifier which is a string of 13 characters. That identifier is
really the Tag.

So my doubts are:

  • Should I set the custom identifier as the primary key and remove the
    default id?
  • Or should I keep the default Id but instead fill it with the custom
    identifier?
  • Would it make any difference when thinking of performance?

I’m currently adding some statistics record for each of those Tags. So
one tag “has_many” statistic records. And this statistics record has the
Tag identifier stored. That’s when I thought that the common key to tie
them together should be the custom identifier instead of the default id.

Any opinions? I hope I managed to explain my doubts.

Cheers.

On 14 May 2011 13:04, comopasta Gr [email protected] wrote:

So my doubts are:

  • Should I set the custom identifier as the primary key and remove the
    default id?

No

  • Or should I keep the default Id but instead fill it with the custom
    identifier?

No

  • Would it make any difference when thinking of performance?

I doubt it.

I’m currently adding some statistics record for each of those Tags. So
one tag “has_many” statistic records. And this statistics record has the
Tag identifier stored.

Why store the tag identifier in the statistic? You have the tag_id
presumably. If you need to show the tag itself it is
statistic.tag.identifier or whatever it is called.

Colin

Colin L. wrote in post #999008:

On 14 May 2011 13:04, comopasta Gr [email protected] wrote:

So my doubts are:

  • Should I set the custom identifier as the primary key and remove the
    default id?

No

  • Or should I keep the default Id but instead fill it with the custom
    identifier?

No

  • Would it make any difference when thinking of performance?

I doubt it.

I’m currently adding some statistics record for each of those Tags. So
one tag “has_many” statistic records. And this statistics record has the
Tag identifier stored.

Why store the tag identifier in the statistic? You have the tag_id
presumably. If you need to show the tag itself it is
statistic.tag.identifier or whatever it is called.

Colin

Thanks Colin.

Why store the tag identifier in the statistic?
Externally the tag is known by its identifier. They are tags that are
read with the mobile and when they come to the server they are found by
this identifier. When a stat is created the tag where it belongs is also
found by the identifier (creation of a stat is not triggered by a tag
being read).

Yes, when the stat is created I could first use the tag identifier I
get, find the internal tag ID and actually store that internal ID with
the stats instead of the identifier. Then the relationship would be
complete. But I guess I was trying to save that db call since if I would
use the identifier for both that call wouldn’t be needed.

Cheers.

On 17 May 2011 11:06, comopasta Gr [email protected] wrote:

Colin L. wrote in post #999008:


Why store the tag identifier in the statistic?

use the identifier for both that call wouldn’t be needed.
It is almost always a bad idea to store the same data twice in the
database (or in this case many times, in the tag and in each
statistic). One issue is that it becomes very difficult to edit the
tag as you have to change it in all the statistics, and the updates
have to be protected by transactions in case a problem arises half way
through. My advise is always to do it the simplest way initially and
only worry about efficiency if such a problem arises. The bottlenecks
in an app almost always turn out to be not where they are initially
expected and time spent optimising the app before problems arise is
time wasted. Also by ending up with more complex code then bugs are
more likely and can be more difficult to fix.

Also in Rails it is almost always best to stick to the conventions
(using id as the primary key in this case), the conventions can be
overridden but usually this just adds complexity and makes life more
difficult.

Colin

Colin

Don’t forget, you can also add a database index to a field that is going
to
be searched often, that will improve search performance.

In your model’s migration:

add_index(table_name, column_names, options)

from: http://api.rubyonrails.org/classes/ActiveRecord/Migration.html
http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

Got it. I’ll stick to the conventions unless really needed otherwise
later.

Thanks a lot for your comments.

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