Forum: Ruby on Rails EAV Model vs Rails

Hi,

I have a relational database (MySQL) with 200 tables in it. Now I want
to reduce number of tables (If it helps in improving the
application).

One approach is to use EAV database model. In which we can use a table
to store ID and manadatory details and
other table to store rest of the details in pair of attribute, and its
value rowwise.

for example look to tables

Client Table
ClientID                 FirstName                    LastName
 1                          Rocky                          B

ClientAttribute Table

ClientID(f.k)         Attribute             AttributeValue
1                         Age                   23
1                         email                 sssp@gm.com

mean I am using rows to store attributes instead of columns.

So problem is I have to convert, the 200 table database to EAV. Has
anybody worked with
EAV model, know its pros cons, and how to do this in rails.

Please help in anyway.

Thanks and regards
Sumeet

>
> I have a relational database (MySQL) with 200 tables in it. Now I want
> to reduce number of tables (If it helps in improving the
> application).
>
> One approach is to use EAV database model. In which we can use a table
> to store ID and manadatory details and
> other table to store rest of the details in pair of attribute, and its
> value rowwise.
>

If you're doing that a lot in your database, personally I'd recommend
looking at one of the NoSQL types such as CouchDB or Cassandra.  Most of 
my
work is neatly normalised tables, but if I had a lot of really freeform 
data
as you seem to, that's where I'd look.

Cheers,


Andy

>
> If you're doing that a lot in your database, personally I'd recommend
> looking at one of the NoSQL types such as CouchDB or Cassandra.  Most of my
> work is neatly normalised tables, but if I had a lot of really freeform data
> as you seem to, that's where I'd look.
>

On the other hand, if you did keep it the way you want to/describe, you
could do some really nice stuff with method_missing so you could write 
code
like this:

client.email = "sssp@gm.com"
puts client.email

and have it store and retrieve the attribute automatically.  That's a 
lot
better than it would be in other languages.

Cheers,


Andy

On 9 March 2010 18:59, Sumeet Panchal <sumeetpanchal9@gmail.com> wrote:
> So problem is I have to convert, the 200 table database to EAV. Has
> anybody worked with
> EAV model, know its pros cons, and how to do this in rails.

The only EAV data model I've used in anger is the back-end of the PHP
ecommerce system Magento.
It's a very powerful pattern, but has its own limitations (not least
that it's a total nightmare to query manually, and tends to be a
little slower than row modelling patterns.

But, and I'm happy for the more computer science-y bods to correct me,
Rails with ActiveRecord is very tightly bound to the row model of data
- in your change, all the magic of associations and relationships
won't work. It seems the task that faces you to implement EAV is a
massive one... you're pretty much saying "I'm going to write a new
Ruby-based web application framework, and use EAV". Of course, you
might be able to make a "acts_as_eav" plugin, which could use AR
associations of Attributes and Values with (as Andy says)
method_missing? calls to act *like* an EAV model  - so you can keep
the core of AR, but include the flexibility of EAV at will. Maybe this
"plugin" approach is likely to be easier with Rails 3 - which isn't
necessarily so locked to AR...

Let's go back to the problem (as we are, at heart, looking for ways to
implement the solution you've decided on, rather than figuring which
solution to use to address a problem) - you have 200 tables (that's a
lot!). Do they all map to AR associations? What do they all do? Is
there not a easy ORM approach that will suffice rather than EAV?

I'd *love* to see an easy to use EAV option for Rails - but I'd
imagine you need to be a "Zed Shaw"/"Hiro Protagonist" to write it...

Sumeet Panchal wrote:
> Hi,
> 
> I have a relational database (MySQL) with 200 tables in it. Now I want
> to reduce number of tables (If it helps in improving the
> application).

Why?  There's nothing wrong with having 200 tables if they're necessary 
to model your data properly.

On the other hand, 200 is a high number, and you could probably stand 
some normalization or something.

> 
> One approach is to use EAV database model.
[...]

And it's a *very* bad approach.  Don't do this unless there is no other 
way to model your data sensibly.  If you can say more about your schema, 
perhaps we can offer better suggestions.

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen@marnen.org