From: Brian Candler <b.candler@...>
Date: 2010-06-16T21:16:33+09:00
Subject: Re: Compare two objects

Greg Ma wrote:
> I have an array of events comming from a database and I have a new
> object (so without an id).

All objects have an object_id, so I presume you mean an "id" 
property/column. If you were using ActiveRecord, that's what you'd get 
by default.

> Is there a simple way to compare my object or I will have to compare
> each attribute?

You'll have to look for another row in the database which matches on all 
the columns which matter to you.

For example: you might consider that a 'User' already exists if there is 
an existing row with the same E-mail address - but you don't care if it 
has a different password or different last_login_time or whatever. In 
that case:

  u = User.new(...)
  if User.find_by_email(u.email)
    raise "That email address is already taken"
  end

There is a race condition here, in that after testing for the 
non-existence of this user, another process could create it. So the 
safest way to deal with this is to have a unique constraint in the 
database itself.
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