Dynamic creation of models and/or tables in Rails

I’m working on a project at the moment that has a rather unusual
requirement and I’m hoping to get some advice on the best way to handle
it
or even some pointers to info that can help me build a solution.

Ok, so this is what I need to do. The application stores and manages
various types of media files but each deployment of the application has
completely different metadata requirements for the media files.

This metadata can contain an arbitrary number of fields of different
types
(single line text, multi-line text, checkboxes, selected values, etc.)
and
also often requires validation particularly presence and uniqueness
validations.

The application needs to be able to easily retrieve values and most
importantly
has to be able to handle full searching capabilities on
these
fields.

One option I considered was using a property list arrangement where the
database table simply contained a property name and value for each
metadata
field of each media file. However, when prototyping this solution it
quickly became apparent that it simply wasn’t going to be efficient
enough
for the searching and retrieval of records particularly when the
database
can be reasonably large e.g. a recent deployment had 3000 media files
and
there were over 20 metadata fields. Also, the queries to do a search and
retrieve the relevant records quickly became very complex.

Another option that the system is currently using is that the metadata
config is defined upfront and a migration is run during deployment to
create a the table and model with a standard name so that the media
model
can be associated with it which the system then uses. This generally
works
pretty fine but it does cause some significant deployment and testing
issues.

For example, writing unit tests becomes much more challenging when you
don’t know the config until deployment. Although I could write a sample
config and test the code that way, it won’t allow me to test the
specific
requirements of a particular deployment.

Similarly, in development, it currently requires me to copy a migration
from the config into the main folder, run it, do all of my testing and
development and then I have to remember to rollback and remove that
migration from the main folder so that the application is in a standard
state. This particularly becomes challenging when I’m bug fixing and I
need
to have the application in a specific configuration for testing and
debugging purposes. Trying to switch between the various configurations
becomes a real nightmare.

Ideally, what I would like is to be able to dynamically create the table
and model including validations, etc. from a config file when the server
is
started. Even better would be if I could maintain multiple metadata
setups
in the one database with each one having its own table so that all I
need
to do to switch between them is change which config file the application
is
currently using.

I’m sure this can be done with Rails but there is very little
information
that I’ve been able to find that can point me in the right direction of
how
to build it during my research over the past few days so any help or
suggestions would be much appreciated!

I guess I would probably use the one table, and use single table
inheritance on each of your “deploys” if I’ve understood what you mean
correctly.

Each subclass model could “rename” fields according to its purpose… of
course, it all depends what you want to do with the metadata in the end.
There’s no use optimising for speed if flexibility is your requirement.

Julian

On Sun, Apr 14, 2013 at 7:19 PM, [email protected] wrote:

also often requires validation particularly presence and uniqueness
searching and retrieval of records particularly when the database can be
For example, writing unit tests becomes much more challenging when you don’t
debugging purposes. Trying to switch between the various configurations
that I’ve been able to find that can point me in the right direction of how
to build it during my research over the past few days so any help or
suggestions would be much appreciated!

So, this is after about 5 minutes thought, so bear that in mind. :slight_smile:

Working on the premise that metadata is basically a key-value sort of
thing, maybe you could split it out of the application proper, and use
a Rails engine serving it up via a MongoDB implementation. The Rails
app proper could do all the normal sorts of things you have, and the
engine can be used to handle just the metadata parts. The app can
remain metadata agnostic that way, and provide the needed elements
based upon the information it retrieves from the engine.

Going a step further, you could combine more front end intelligence
into the app, say via backbone.js and underscore.js, and use them to
interact with the metadata serving part of your app.