Rails - Sep 2007 - modeling a collection of integers in active record

Hey,

I''m a newbie to Rails, so forgive me if my question is stupid and
I''m
spamming the group. I couldn''t find any info on the Web.

I''d like to model an entity that contains a collection of integers. In
SQL, I could achieve that by creating two tables, like that:

CREATE TABLE Entity (
    id INTEGER,
    title VARCHAR,
    other_stuff BLOB
);

CREATE TABLE EntityIntegerCollection (
    entity_id INTEGER,
    value INTEGER
);

And now I can SELECT value FROM EntityIntegerCollection WHERE
entity_id = 1234 to retrieve the collection for entity 1234. My
question is: How do I model this in ActiveRecord? Can I keep this
simple table schema or do I have to change something to get what I
want?


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Well, you start with creating a model for every table, which can be done 
like when you create controllers.

ruby script/generate model entity
ruby script/generate model entityintegercollection

and in your migration you can add columns :D

db/migrate/ (HERE)



-- 
Posted via http://www.ruby-forum.com/.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Uhm, I think I''m not following you...

What I want is to create a SQL table structure, so that later in Rails
I can write something like entity.integer_collection[3]. I''m looking
for a way to express this association using has_many, belongs_to or
something like that... I don''t want to stick to the table schema
mentioned, but I want to have Entity class that has attribute
integer_collection. Do you mean I can achieve this with migrations?

Mike

On Sep 3, 8:25 pm, Jamal Soueidan
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> Well, you start with creating a model for every table, which can be done
> like when you create controllers.
>
> ruby script/generate model entity
> ruby script/generate model entityintegercollection
>
> and in your migration you can add columns :D
>
> db/migrate/ (HERE)
>
> --
> Posted viahttp://www.ruby-forum.com/.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Let me first answer your question directly and then suggest an
alternative.

First of all, let''s follow rails convention here and create two
tables: entities and entity_integers. We''ll also create the models
that rails will use to interface them. We''ll do both at once with:

ruby script/generate model Entity
ruby script/generate model EntityInteger

You will find two new migrations in db/migrate:

001_create_entities.rb
002_create_entity_integers.rb

In those add your columns:

class CreateEntities < ActiveRecord::Migration
  def self.up
    create_table :entities do |t|
      t.column :title, :string
    end
  end

  def self.down
    drop_table :entities
  end
end

Similarly in your 002_create_entity_integers.rb migration add:

t.column :value, :integer
t.column :entity_id, :integer

in your Entity model (app/models/entity.rb) add:

has_many :entity_integers

and in your EntityInteger model add:

belongs_to :entity

Run rake db:migrate and that''s it. open up script/console and play
around.

@entity = Entity.new :title => "foo"
@entity.save
@entity.entity_integers.create :value => 1
@entity.entity_integers.create :value => 2

@entity.entity_integers.map {|integer| integer.value} #=> [1, 2]


Now here''s an alternative. Create the same Entity model as before but
in the migration do:

t.column :title, :string
t.column :integrers, :string, :default => [].to_yaml # will work in
MySQL but not Postgres, last time I checked.

and in the Entity model:

seialize :integers, :class_name => Array

and try this out:

@entity = Entity.new :title => "foo"
@entity.integers += [1,2,3]
@entity.save
@entity.integers #=> [1,2,3]
@entity.integers += [5,6,7]
@entity.save
@entity.integers #=> [1,2,3,5,6,7]

Now @entity.integers is transparently serialized into the database as
an array.

Just another option.

Rein

On Sep 3, 1:19 pm, jasiu85
<jasi...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hey,
>
> I''m a newbie to Rails, so forgive me if my question is stupid and
I''m
> spamming the group. I couldn''t find any info on the Web.
>
> I''d like to model an entity that contains a collection of
integers. In
> SQL, I could achieve that by creating two tables, like that:
>
> CREATE TABLE Entity (
>     id INTEGER,
>     title VARCHAR,
>     other_stuff BLOB
> );
>
> CREATE TABLE EntityIntegerCollection (
>     entity_id INTEGER,
>     value INTEGER
> );
>
> And now I can SELECT value FROM EntityIntegerCollection WHERE
> entity_id = 1234 to retrieve the collection for entity 1234. My
> question is: How do I model this in ActiveRecord? Can I keep this
> simple table schema or do I have to change something to get what I
> want?

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Thats fantastic Rein,

I wanted something similar to Mike above, at the moment i manually
unload and load (with YAML) a whole bunch of floats from a binary
field.
Your second solution can make my code much cleaner.

I presume the string size can be enlargened with something
like  :limit => 1.megabyte   in the migration file?

cheers,
J


On Sep 3, 8:59 pm, Rein Henrichs
<rein.henri...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Let me first answer your question directly and then suggest an
> alternative.
>
> First of all, let''s follow rails convention here and create two
> tables: entities and entity_integers. We''ll also create the models
> that rails will use to interface them. We''ll do both at once with:
>
> ruby script/generate model Entity
> ruby script/generate model EntityInteger
>
> You will find two new migrations in db/migrate:
>
> 001_create_entities.rb
> 002_create_entity_integers.rb
>
> In those add your columns:
>
> class CreateEntities < ActiveRecord::Migration
>   def self.up
>     create_table :entities do |t|
>       t.column :title, :string
>     end
>   end
>
>   def self.down
>     drop_table :entities
>   end
> end
>
> Similarly in your 002_create_entity_integers.rb migration add:
>
> t.column :value, :integer
> t.column :entity_id, :integer
>
> in your Entity model (app/models/entity.rb) add:
>
> has_many :entity_integers
>
> and in your EntityInteger model add:
>
> belongs_to :entity
>
> Run rake db:migrate and that''s it. open up script/console and play
> around.
>
> @entity = Entity.new :title => "foo"
> @entity.save
> @entity.entity_integers.create :value => 1
> @entity.entity_integers.create :value => 2
>
> @entity.entity_integers.map {|integer| integer.value} #=> [1, 2]
>
> Now here''s an alternative. Create the same Entity model as before
but
> in the migration do:
>
> t.column :title, :string
> t.column :integrers, :string, :default => [].to_yaml # will work in
> MySQL but not Postgres, last time I checked.
>
> and in the Entity model:
>
> seialize :integers, :class_name => Array
>
> and try this out:
>
> @entity = Entity.new :title => "foo"
> @entity.integers += [1,2,3]
> @entity.save
> @entity.integers #=> [1,2,3]
> @entity.integers += [5,6,7]
> @entity.save
> @entity.integers #=> [1,2,3,5,6,7]
>
> Now @entity.integers is transparently serialized into the database as
> an array.
>
> Just another option.
>
> Rein
>
> On Sep 3, 1:19 pm, jasiu85
<jasi...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> > Hey,
>
> > I''m a newbie to Rails, so forgive me if my question is stupid
and I''m
> > spamming the group. I couldn''t find any info on the Web.
>
> > I''d like to model an entity that contains a collection of
integers. In
> > SQL, I could achieve that by creating two tables, like that:
>
> > CREATE TABLE Entity (
> >     id INTEGER,
> >     title VARCHAR,
> >     other_stuff BLOB
> > );
>
> > CREATE TABLE EntityIntegerCollection (
> >     entity_id INTEGER,
> >     value INTEGER
> > );
>
> > And now I can SELECT value FROM EntityIntegerCollection WHERE
> > entity_id = 1234 to retrieve the collection for entity 1234. My
> > question is: How do I model this in ActiveRecord? Can I keep this
> > simple table schema or do I have to change something to get what I
> > want?- Hide quoted text -
>
> - Show quoted text -

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---