# Noob ActiveRecord Join Question

**URL:** <https://www.ruby-forum.com/t/noob-activerecord-join-question/52018>\
**Category:** Rails\
**Created:** [January 10, 2006, 4:28am UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018 "2006-01-10T04:28:46Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 10, 2006, 4:28am UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/1 "2006-01-10T04:28:46Z")

</div>

I’m new to rails and ruby, and after trying to get this to work  
correctly for hours, I thought I’d give this forum an try.

I’ve setup a trivial project just to mess around with Rails database  
naming conventions and associations.

I’ve got a table called Pets, and a table called Types.  
Pets contains a list of pets, Parky the cat, Daisy the dog, etc, And  
Types contains a list of different pet types, dog - cat - fish - bird -  
etc.

Pets table  
CREATE TABLE `pets` (  
`id` int(11) NOT NULL auto\_increment,  
`name` varchar(20) default NULL,  
`pet_id` int(11) default NULL,  
PRIMARY KEY (`id`)  
) ENGINE=MyISAM DEFAULT CHARSET=latin1

Types table  
CREATE TABLE `types` (  
`id` int(11) NOT NULL auto\_increment,  
`pettype` varchar(11) default NULL,  
PRIMARY KEY (`id`)  
) ENGINE=MyISAM DEFAULT CHARSET=latin1

What I want to do is to associate the pet\_id from Pets with the id from  
types, and can do that in SQL like this:

select pets.\*, types.pettype  
from pets, types  
where pets.id = 1  
and pets.pet\_id = types.id

In Rails, I have two models, 1 for pets, 1 for types

class Type \< ActiveRecord::Base  
belongs\_to :pet  
end

class Pet \< ActiveRecord::Base  
has\_one :type, :foreign\_key =\> “id”  
end

What I end up with is this SQL statement out of Rails:

select pets.\*, types.pettype  
from pets, types  
where pets.id = 1  
and pets.pet\_id = 1

Where 1 is the primary key (id) of the pets row.

Just wondering what I’m doing wrong.

Thanks!

---

<div class="post-metadata">

**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 10, 2006, 5:06am UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/2 "2006-01-10T05:06:36Z")

</div>

I just made the same mistake a few hours ago. I ended up flipping the  
belongs\_to: and has\_one: in my Models and it works. So:

class Type \< ActiveRecord::Base  
has\_one :pet  
end

class Pet \< ActiveRecord::Base  
belongs\_to :type  
end

You don’t need the foreign key either, rails handles that  
automagically. I have no idea if this is right, just that it does  
what I want it to do.

On Jan 9, 2006, at 7:28 PM, David Mr. wrote:

> etc.  
> CREATE TABLE `types` (  
> select pets.\*, types.pettype  
> class Pet \< ActiveRecord::Base  
> Where 1 is the primary key (id) of the pets row.  
> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
> 
> * * *
> 
> Rails mailing list  
> removed\_email\_address@domain.invalid  
> [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails)

- Bill

---

<div class="post-metadata">

**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 10, 2006, 5:11am UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/3 "2006-01-10T05:11:26Z")

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David Mr. wrote:

> class Type \< ActiveRecord::Base  
> belongs\_to :pet  
> end

As a rule, I would stay away from using “type” as a model name or a  
column name. ‘type’ is a reserved ruby keyword, and “type” columns are  
automagic for single table inheritance.

You are likely to run into all sorts of wierdness if you use them  
outside of those contexts.

\_Kevin

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<div class="post-metadata">

**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 10, 2006, 7:31pm UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/4 "2006-01-10T19:31:37Z")

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Tried that and it still didn’t work for me.

This works, but not as pretty as just saying has\_one and belongs\_to ☹

def self.find\_all\_with\_pettypes(j)  
find :all,  
{  
:conditions =\> “id = ‘#{j}’”,  
:joins =\> ‘LEFT JOIN types ON pets.petid = types.petid’  
}  
end

Guess as I play with Rails more I might actually learn what I’m doing.  
Thanks for they help!

Bill P. wrote:

> I just made the same mistake a few hours ago. I ended up flipping the  
> belongs\_to: and has\_one: in my Models and it works. So:
> 
> class Type \< ActiveRecord::Base  
> has\_one :pet  
> end
> 
> class Pet \< ActiveRecord::Base  
> belongs\_to :type  
> end

---

<div class="post-metadata">

**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 10, 2006, 9:11pm UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/5 "2006-01-10T21:11:01Z")

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I don’t think this is correct. You should have the belongs\_to call in  
the class that contains the foreign key. So it does not make sense to  
say that Type belongs\_to :pet. You had it right the first time.

I agree with Kevin, however, I would stay away from “type” as a model  
name or attribute.

Lance

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<div class="post-metadata">

**Author:** ![pezdude](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/a87d85/32.png) [@pezdude](https://www.ruby-forum.com/u/pezdude)\
**Post date:** [January 11, 2006, 2:01am UTC](https://www.ruby-forum.com/t/noob-activerecord-join-question/52018/6 "2006-01-11T02:01:08Z")

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So, I tried this once, and it didn’t work. I tried it again, and it did  
work.

Now it’s working!!!

Thanks, just needed to wrap my head around it for it to make sense  
(although it still seams backwards to me 🙂

Thanks again!

Bill P. wrote:

> I just made the same mistake a few hours ago. I ended up flipping the  
> belongs\_to: and has\_one: in my Models and it works. So:
> 
> class Type \< ActiveRecord::Base  
> has\_one :pet  
> end
> 
> class Pet \< ActiveRecord::Base  
> belongs\_to :type  
> end