Design decision: Dynamically adding data question


#1

I need to give users the ability to optionally add metadata to
documents. Another way to state this is the fact that users need to add
at least 5 categories to a document.

Basically what I want to do is dynamically add metadata (or categories)
to a document on an ad hoc basis. Here are the options that I have
thought of:

Option 1:
Should I do this by dynamically creating new table columns in the
database?

Option 2:
Should I define 5 columns called
attirbute1,attirbute2,attirbute3,attirbute4,attirbute5 and then only use
and show them if the user requires the attributes.

Option 3:
Should I create a metadata table that keeps track of the columns and the
data associated with them?

What do you think is the best way to achieve this? Can you think of any
other ways to easily add this functionality. The problem is that the
functionality needs to be very generic.


#2

I would create a “meta” table with two columns: “data” and
“document_id”. This
way is much more neat and tidy; each metadata attribute, for each
document,
will be it’s own row. Trying to dynamically add columns or whatever
could
become disasterous. Go easy on yourself and use an AR association like
this:

Document
has_many :metas

Meta
belongs_to :document

Document.metas will return all of the metadata attributes associated
with the
document, however many there may be.

My naming skills suck, I think you can come up with a better model name
than “meta”, but you get the idea. As far as being “very generic”… I
don’t
know what that’s supposed to mean. I hope this is generic enough for
you.


#3

Sent from my iPhone

On 20 Oct 2008, at 16:37, David S. <rails-mailing-list@andreas-
s.net> wrote:

Option 1:
Should I do this by dynamically creating new table columns in the
database?

Yuck

Option 2:
Should I define 5 columns called
attirbute1,attirbute2,attirbute3,attirbute4,attirbute5 and then only
use
and show them if the user requires the attributes.

May not be flexible enough

Option 3:
Should I create a metadata table that keeps track of the columns and
the
data associated with them?

I would go that way. Your metadata table just stores triples: id of
the parent, the name of the piece of data and its value

Fred