From: Josh Cheek <josh.cheek@...>
Date: 2010-03-30T18:03:03+09:00
Subject: Re: Fastest Array Search?

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On Tue, Mar 30, 2010 at 2:38 AM, Derek Cannon <novellterminator@gmail.com>wrote:

> > Primary keys and unique indexes in the database ensure that you don't
> > have duplicated rows.
> > Are you using ActiveRecord?
>
> I don't even know what that means yet. I just started with Rails a few
> days ago. I just created a project, created a database with the fields I
> want, and used scaffold. I can add/edit/delete elements of my database,
> that's pretty much all. I've already written a class that will parse XML
> files for data, load that data into an array of instantiated classes
> called "Movie". For example, each Movie class has a title, rating, plot,
> etc. I just want to make sure the movie's title and release date don't
> already exist in a database before I add them. For example, I was
> thinking of something like this:
>
> # @movie_db is the Rails SQLite3 database
> # @movies holds the temporary array of all the Movie classes,
>             #each which have many variables: title, rating, plot, etc
>
> @movies.each { |i|
>     if @movie_db.find { |x| (x["title"] == i.title) and
> x["release_year"] == x.release_year } == false
>        @movie_db = MovieDb.new("title"=>i.title,"plot"=>i.plot,etc)
>        @movie_db.save
>     end
> end
>
> ^ This is just the basic code. It makes sure @movies elements will only
> be added if a movie is unique (based on title and release date (since
> there are some movies with the same name, but none that I can think of
> with the same name AND release year)).
> --
> Posted via http://www.ruby-forum.com/.
>
>
Hi, Derek, there is a ML specifically for Rails
http://groups.google.com/group/rubyonrails-talk

The short answer is that you're doing way too much work (and what a nice
short answer that is :)

You don't need to worry about the DB as much as you are, let ActiveRecord do
that for you. Your model can declare validations that need to be met, such
as "this attribute should be unique", and then AR will not save any data to
the db if that validation does not pass.

In your case, the model might look like this
class Movie < ActiveRecord::Base
  validates_uniqueness_of :title , :scope => :genre , :message =>
"title/genre pair must be unique"
end

Here is an example that shows a session, where I create several movies, some
of which are duplicates. You see that it does not save the duplicates
because they fail this validation. Then I query the db for all the movies it
contains, and you will see that there are no duplicate movies listed in
there.

http://img202.imageshack.us/img202/213/picture6os.png



You shouldn't be replicating the db in memory, and you shouldn't be
validating data outside your model like this (I assume this code is in your
controller).

Anyway, hope that helps, and for an exceptionally good resource on Rails,
check out guides.rubyonrails.org In this particular case, the information to
create the validation was in the guide titled "Active Record Validations and
Callbacks". I know there is a lot there, but with all seriousness, the time
you spend reading these, and getting familiar with what is available (even
if it's just to make a mental note of it, and then later look it up when you
need it) will save you hundreds more time and effort (and lets not forget
frustration) in the long run. Because Rails will do things for you that just
make your life so much easier, and that you might spend several days working
on to create a slower buggier solution to something there is already a
method for, or that AR already accounts for. I speak from experience on that
:P

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