Dynamically create databases?

Rails
1

Is it possible to dynamically create new databases and tables within
them
with Rails?

Or is that a task best done manually?

I’m creating an application which should allow users to store their own
statistics information (which can and probably with time will be a lot).
My initial thought was to give each user their own database to keep
their
data separate from each other due to the possible large quantity of data
each user will have.

Good idea? Bad idea? Other ways to do it?

2

Yes, and yes.

That sounds fine.

Just be careful not to optimise prematurely (ie… make design decisions
with a VIEW to the future, but don’t let that both you too much in the
present). Chances are when it comes to architecture and optimisation, Ya
Aint Gonna Need It, and when you do, it’ll most likely be different than
you think it will be now.

Focus more on the classes in your system than how to efficiently store
them at the inception/design stage.

Julian

3

Thanks for replying, Julian.

Can you point me to any resources that describe how to do it?

I agree that I should not optimize prematurely but what I’m considering
is
which is easier,
to go with dynamically creating databases from the start or to extract
data
from the single database to new databases later on?

It’s at least something to keep in the back of my mind.

4

On 4 April 2013 07:29, Johan V. [email protected]
wrote:

Good idea? Bad idea? Other ways to do it?

What do you mean by a large quantity of data? Modern databases can
manage vast amounts of data efficiently. It is very rare for the
bottlenecks in a system to be where you expect them to be when you
start out and it is very likely that you will find that the extra work
was a waste of time. Start with a single database and make sure you
have good automated test coverage. Then in the unlikely event that
you find that you do have split the database then you can refactor the
code and the tests will help to ensure that you have not messed
anything up.

Colin

5

Thanks for posting, I appreciate the feedback.

I’ll start with keeping everything within a single database and take it
from there.

You are right Julian in that I am new with RoR and what I’ve asked for
is
advanced.

I’m still curious though how creating databases dynamically would be
done
so if it’s explained anywhere I’d love to read it!

2013/4/4 Julian L. [email protected]

6

On 04/04/2013, at 6:05 PM, Johan V. [email protected]
wrote:

Thanks for replying, Julian.

Can you point me to any resources that describe how to do it?

I agree that I should not optimize prematurely but what I’m considering is which
is easier,
to go with dynamically creating databases from the start or to extract data from
the single database to new databases later on?

It’s at least something to keep in the back of my mind.

Hi,

You shouldn’t attempt to do this if you don’t already understand enough
Ruby / Rails to do it yourself.

So, I suggest sticking with what you can do first.

This might sound like a cop out, but there’s very good reason. It’s very
advanced Rails and you really shouldn’t attempt something like this
until you understand the basics really well IMHO.

Julian

7

Assuming you are using postgresql you might be interested in this
railscast (paid)

Which takes advantage of being able to have multiple schemas in
PostgreSQL.

Be aware though that it will make your initial coding more complicated
and will
have knock-on effects for things like testing etc.

Basically, it will do what you want but it will not be free in terms of
development effort.

I echo other statements that this may be premature optimisation, look at
the railscast, give
it a try yourself and see if the trade-off is good enough for you.

(If you do not want to pay for railscasts then have a look at this gem:
GitHub - influitive/apartment: Database multi-tenancy for Rack (and Rails) applications)

8

We have toyed with creating separate databases for each customer as our
combined one is starting to get quite large. In our case, the models
will
always be the same no matter which database you are connecting to, so
there isn’t any meta-programming involved. It’s just a case of switching
databases to the correct one for that customer once they log into the
system.

One thing to consider is that shared data needs to go somewhere
(sessions,
username/passwords etc) as well.

Cheers
Simon

On Thu, 04 Apr 2013 16:34:21 +0800, Julian L.

9

Okay…

So to do this, you need to understand meta-programming to a degree
because that’s what you’re doing.

In normal Rails, you’d create a model as part of the development
process, but what you’re doing is creating some code that creates models
itself (ie one level of abstraction higher than normal).

The equivalent straight ruby comparison is: (compare 1, with 2, below):

  1. Creating a class (this is normal programming)

class Cat
def hi
puts ‘meow’
end
end

You can then create new Cat objects like this:
furrycat = Cat.new

and make it meow like this:
furrycat.hi

  1. Creating a piece of code that creates a class (this is
    meta-programming)

a_class = Class.new
hi_method_block = Proc.new{ puts ‘meow’ }
a_class.send(:define_method, :hi, &hi_method_block)

You can then create new “Cat” objects like this:
furrycat = a_class.new

and make it meow like this:
furrycat.hi

So… assuming you followed that, then you’ll understand that you could
do the same thing with ActiveRecord::Base classes, which is what forms
the bases for Active Record model classes. This is how you’d dynamically
LOAD one of your programmatically generated models. Creating the table
is just a matter of executing some arbitrary SQL which can be built
using ActiveRecord::Base.connection.execute. (Eg to run a count of a
fictitious users table, you’d do this:
ActiveRecord::Base.connection.execute(“SELECT COUNT(*) FROM users;”)

However, like I said, there’s no point trying to do this until you can
walk, because this really is running. Most Rails devs hardly ever get
into this stuff. I’ve been a Rails developer since 2005, and I’ve only
done this sort of dynamic table and database thing once or twice in
practice.

Julian

10

Hello!

I know three years have passed, but I am looking to do exactly what you
proposed on your first post, so I am interested in knowing if you have
managed to so and if you did, how did you do it?

Thanks in advance.

quinta-feira, 4 de Abril de 2013 às 05:24:18 UTC-4, Johan V.
escreveu:

11

That kind of scenario was what I had initially in mind. Everyone has
the same models, just not the same database.

2013/4/4, Simon M. [email protected]: