# activerecord has\_many vs. has\_one scope

**URL:** <https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147>\
**Category:** rubyonrails-talk\
**Created:** [October 27, 2009, 8:47pm UTC](https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147 "2009-10-27T20:47:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Chris\_Drappier](https://avatars.discourse-cdn.com/v4/letter/c/ce7236/32.png) [@Chris\_Drappier](https://discuss.rubyonrails.org/u/Chris_Drappier)\
**Post date:** [October 27, 2009, 8:47pm UTC](https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147/1 "2009-10-27T20:47:37Z")

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Hi All,

in the api for has\_many, under the :conditions option we see :

```
Specify the conditions that the associated objects must meet in order to be

```

included as a `WHERE` SQL fragment, such as `price > 5 AND name LIKE ‘B%’`. Record creations from the association are scoped if a hash is used. `[has_many](http://www.railsbrain.com/api/rails-2.3.2/doc/index.html?a=M001885&name=has_many) :posts, :conditions => {:published => true}` will create published posts with `@blog.posts.create` or `@blog.posts.build` .

however, in the api for has\_one under the :conditions option we see :

```
Specify the conditions that the associated object must meet in order to be

```

included as a `WHERE` SQL fragment, such as `rank = 5` .

So, we can’t automatically scope associated has\_one records by conditions like we can has\_many. seems to me that the behavior should be the same in both situations.

I have a model with relationships like this

class ThingContainer \< AR::Base has\_one :blue\_thing, :class\_name =\> “Thing”, :conditions =\> {:color =\> “blue”} has\_one :red\_thing, :class\_name =\> “Thing”, :conditions =\> {:color =\> “red”} end

class Thing \< AR::Base belongs\_to :thing\_container end

but when I call ThingContainer.build\_blue\_thing, it does not populate the color attribute. is this by design? or something that was simply left out?

-C

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**Author:** ![Eric9](https://avatars.discourse-cdn.com/v4/letter/e/ac91a4/32.png) [@Eric9](https://discuss.rubyonrails.org/u/Eric9)\
**Post date:** [October 27, 2009, 9:48pm UTC](https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147/2 "2009-10-27T21:48:20Z")

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You appear to be trying to fit has\_one into an implementation it wasn't designed for. The has\_one is supposed to be exactly that: ThingContainer has\_one Thing, but you actually have ThingContainer has\_many :things # well, really one of each of different kinds.

There are likely several ways to handle this situation, but my instinct is to use named scopes for the color finds and validations to enforce the one-of-each. Another way would be to use STI to set up color models that inherit from Thing, with the has\_ones from ThingContainer pointing to each.

-eric

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**Author:** ![Matt\_Jones](https://avatars.discourse-cdn.com/v4/letter/m/258eb7/32.png) [@Matt\_Jones](https://discuss.rubyonrails.org/u/Matt_Jones)\
**Post date:** [October 28, 2009, 1:26am UTC](https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147/3 "2009-10-28T01:26:43Z")

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This was just fixed on September 28:

[https://rails.lighthouseapp.com/projects/8994/tickets/3088](https://rails.lighthouseapp.com/projects/8994/tickets/3088)

--Matt Jones

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**Author:** ![Chris\_Drappier](https://avatars.discourse-cdn.com/v4/letter/c/ce7236/32.png) [@Chris\_Drappier](https://discuss.rubyonrails.org/u/Chris_Drappier)\
**Post date:** [October 28, 2009, 2:26pm UTC](https://discuss.rubyonrails.org/t/activerecord-has-many-vs-has-one-scope/47147/4 "2009-10-28T14:26:59Z")

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so, will we see this patch applied in 2.3.5?