Model association question

Rails
1

I have a question about how best to model a pair of
properties/attributes in Rails3. The generic “models” are:

class Foo < ActiveRecord::Base
end
class Bar < ActiveRecord::Base
end

I want Foo to have two associations with Bar, along the lines of
‘has_one’ for each association, where I can work with each, as in bar1
and bar2. ‘has_many’ would work, but it would be extra work to have to
fish the correct one out of the array, and isn’t as elegant a way to
model the relationships.

Thanks

Randy

2

On 9/13/11 1:22 PM, Randy R. wrote:

and bar2. ‘has_many’ would work, but it would be extra work to have to
fish the correct one out of the array, and isn’t as elegant a way to
model the relationships.

Thanks

Randy

I suppose that it could be done with a has_one relationship repeated as
such
class Foo < AR::B
belongs_to :bar1, class_name => “Bar”, :foreign_key => “bar1_id”
belongs_to :bar2, class_name => “Bar”, :foreign_key => “bar2_id”
end

Mind you this is not a very elegant way of doing it, but it is adhering
to KiSS principles.

On the Bar end of things, how should the relationship play out? Should
it only be able to be associated to one Foo?

Also are do bar 1 and bar 2 behave differently or have any
characteristic that distinguish them. In other words, are all bar1’s
always going to be bar1’s? if so you can do a normal has many
relationship with a limit of 2 children and then scopes on the bar model
to make up the difference.

Jesse

3

On 09/13/2011 03:34 PM, Jesse wrote:

‘has_one’ for each association, where I can work with each, as in
class Foo < AR::B
Also are do bar 1 and bar 2 behave differently or have any
characteristic that distinguish them. In other words, are all bar1’s
always going to be bar1’s? if so you can do a normal has many
relationship with a limit of 2 children and then scopes on the bar
model to make up the difference.

Jesse

Thanks.

On the Bar end, it would only be associated with the one Foo, yes.

bar1 and bar2 would have different values for their respective
properties, but that is about all. Well, I guess if a Foo got removed,
then so should both of its Bars, but I think I’ve seen how to do that
part.

Randy

4

On 09/13/2011 04:21 PM, Colin L. wrote:

I suppose that it could be done with a has_one relationship repeated as
only be able to be associated to one Foo?
On the Bar end, it would only be associated with the one Foo, yes.

bar1 and bar2 would have different values for their respective properties,
but that is about all. Well, I guess if a Foo got removed, then so should
both of its Bars, but I think I’ve seen how to do that part.
Looking at a Bar can you tell whether it is a bar1 or a bar2 just from
the records contents?

Colin
It is possible to tell bar1 from bar2 from the contents, in the few use
cases I’m thinking of right now, yes.

Randy

5

On 9/13/11 5:17 PM, Randy R. wrote:

I want Foo to have two associations with Bar, along the lines of
as such

On the Bar end, it would only be associated with the one Foo, yes.

You could go the STI route and give each bar its own sub class

class Bar < AR::B
end
class BarOne < Bar
belongs_to :foo
end
class BarTwo < Bar
belongs_to :foo
end

and add the attribute type to Bar

then your Foo class could be
class Foo < AR::B
has_one :bar_one, :dependant => :destroy
has_one :bar_two, :dependant => :destroy
end
with attributes of

the :dependant => :destroy will allow the two bars to be destroyed when
the foo is destroyed.

While a little more work than my original suggestion this will be far
more elegant as you can easily deploy more bars if needed. Also it is
technically more correct as it would seem that 2 bars really belongs to
one foo as deleting the foo should delete the bars, whereas the other
way would make the Bars the parents of the Foo.

6

On 13 September 2011 22:17, Randy R. [email protected] wrote:

end

On the Bar end of things, how should the relationship play out? Should it
Thanks.

On the Bar end, it would only be associated with the one Foo, yes.

bar1 and bar2 would have different values for their respective properties,
but that is about all. Well, I guess if a Foo got removed, then so should
both of its Bars, but I think I’ve seen how to do that part.

Looking at a Bar can you tell whether it is a bar1 or a bar2 just from
the records contents?

Colin