Object.find in HABTM join table?

Rails
1

Good morning,

is it possible to find objects by giving values for the HABTM join table
only?

Example:
menu
id name parents path
1 abc -1 /
2 def 1 /def
3 ghi 1 /ghi
4 jkl 2,1 /jkl
5 mno 2 /mno

that means when I go to /abc the menu consists of menu items with the id
2, 3 and 4. When I go to /def the menu consits of the menu items with
the id 4 and 5 but as you can see menu items can be shown in many menus
but exist only once.

So the tables would look like this:
menus
id name path
1 abc /
2 def /def
3 ghi /ghi
4 jkl /jkl
5 mno /mno

menus_parents
menu_id parent_id
2 1
3 1
4 1
4 2
5 2

So how is it possible to all menu objects that have 1 as parent?
My current approach is:
menus = Menu.all
menus = menus.select{|m| m.parents.include?(1)}

I don’t really like it cause all menu items are loaded from the database
each and every time. Is there any better solution to this like some
find…?

2

On 15 July 2010 09:30, Heinz S. [email protected] wrote:

3 ghi 1 /ghi
id name path
4 1
4 2
5 2

So how is it possible to all menu objects that have 1 as parent?
My current approach is:
menus = Menu.all
menus = menus.select{|m| m.parents.include?(1)}

Can’t you do
menus = Menu.find( :all, :include => :parents, :conditions =>
['parent.id = ?, 1] )
or something similar.

Or even better, if you have the parent object, then all the menus that
have that as a parent are parent.menus

Colin

3

Hey Colin,

thanks but the parent.menus doesn’t work because the habtm is on the
same table:
has_and_belongs_to_many :parents, :class_name => “Menu”,
:association_foreign_key => “parent_id”, :join_table => “menus_parents”

The other suggestion works just fine, thanks!

This is the working code:
@menus = Menu.find(:all, :include => :parents, :conditions =>
[’menus_parents.parent_id = ?’, parent.id])

4

On 15 July 2010 14:22, Heinz S. [email protected] wrote:

Hey Colin,

thanks but the parent.menus doesn’t work because the habtm is on the
same table:
has_and_belongs_to_many :parents, :class_name => “Menu”,
:association_foreign_key => “parent_id”, :join_table => “menus_parents”

I think there may be a better way of doing this. If you made the join
table a proper table with a model then for Menu you could do
has_many children through menus_parents
and also
has_many parents through menus_parents
then you can go both ways more easily.

Colin