Rails - Sep 2005 - Filtering with conditions in the child table/class

hello,
this is probably a simple problem but I havn''t found the elegant/simple
RoR way to solve it.
I have a Parent and a Child table with a has_many :children and a belongs _to
:parent, relationship.
I view all childs through each parent this way:
<% for parent in Parent.find_all %>
    parent.name  parent.other_attribute
        for child in parent.children
            child.name child.age child activity etc
        end
<% end %>

It works fine. 
Now I want the same thing but with a condition in the child table. For example
only the children below a certain age (...WHERE children.age < 12 ) also if
the parent hasn''t got any children below 12 it musn''t appear.

If the condition lay in the parent it''s simple instead of :
Parent.find_all i put : Parent.find(:all, :conditions => "profession =
''doctor''"). But this Parent.find(:all, :conditions =>
"child.age < 12") does not.
My best guess is there would be a method in the model class Child <
ActiveRecord or maybe something with :join ...

thank you for your help
charly

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Charly wrote:
> hello, this is probably a simple problem but I havn''t found the
> elegant/simple RoR way to solve it. I have a Parent and a Child table
> with a has_many :children and a belongs _to :parent, relationship. I
> view all childs through each parent this way: <% for parent in
> Parent.find_all %> parent.name  parent.other_attribute for child in
> parent.children child.name child.age child activity etc end <% end %>
> 
> 
> It works fine. Now I want the same thing but with a condition in the
> child table. For example only the children below a certain age
> (...WHERE children.age < 12 ) also if the parent hasn''t got any
> children below 12 it musn''t appear.
> 
> If the condition lay in the parent it''s simple instead of :
> Parent.find_all i put : Parent.find(:all, :conditions =>
"profession
> = ''doctor''"). But this Parent.find(:all, :conditions
=> "child.age <
> 12") does not.
:conditions is just a lump of SQL, so unless you''ve got the child table
joined to the parent table in the Parent.find() query, it won''t have
anything to do the comparison with.  The following *might* work, but I
haven''t tested it:

Parent.find(:all, :include=>[''child''],
:conditions=>''child.age < 12'')

That should make the join to the child table work, and you won''t get
parents without young children.

By the way, do you have a good reason for storing ages as years?  It''s
usually a better idea to store dates of birth - that way you don''t have
to update all your rows every year :-)

-- 
Alex

Thanks, it worked perfectly, beyond my expectations - really pleased with
rails.
If I understand well the :include argument force RoR to do the associations
which otherwise are only made at runtime (for ex: when the iteration gets to
child.name). Therefore it makes all associated attribute available for
processing in the find() function.

By the way my parent child table were just there for illustration. The real
ones are Lawyer, Matter and Fee. The fees have timestamps and I wanted only
the fees of a given year (no ages stored here)
Charly



"Alex Young" <alex-qV/boFbD8Meu8LGVeLuP/g@public.gmane.org> a
écrit dans le
message de news:
43327F10.2030801-qV/boFbD8MeyI+KclE3oSK1cXZ9k6wlg@public.gmane.org
> Charly wrote:
>> hello, this is probably a simple problem but I havn''t found
the
>> elegant/simple RoR way to solve it. I have a Parent and a Child table
>> with a has_many :children and a belongs _to :parent, relationship. I
>> view all childs through each parent this way: <% for parent in
>> Parent.find_all %> parent.name  parent.other_attribute for child in
>> parent.children child.name child.age child activity etc end <% end
%>
>>
>>
>> It works fine. Now I want the same thing but with a condition in the
>> child table. For example only the children below a certain age
>> (...WHERE children.age < 12 ) also if the parent hasn''t got
any
>> children below 12 it musn''t appear.
>>
>> If the condition lay in the parent it''s simple instead of :
>> Parent.find_all i put : Parent.find(:all, :conditions =>
"profession
>> = ''doctor''"). But this Parent.find(:all,
:conditions => "child.age <
>> 12") does not.
> :conditions is just a lump of SQL, so unless you''ve got the child
table
> joined to the parent table in the Parent.find() query, it won''t
have
> anything to do the comparison with.  The following *might* work, but I
> haven''t tested it:
>
> Parent.find(:all, :include=>[''child''],
:conditions=>''child.age < 12'')
>
> That should make the join to the child table work, and you won''t
get
> parents without young children.
>
> By the way, do you have a good reason for storing ages as years? 
It''s
> usually a better idea to store dates of birth - that way you don''t
have
> to update all your rows every year :-)
>
> -- 
> Alex

Charly wrote:
> If I understand well the :include argument force RoR to do the associations
> which otherwise are only made at runtime (for ex: when the iteration gets
to
> child.name). Therefore it makes all associated attribute available for
> processing in the find() function.
That''s it - it forces greedy evaluation.  The availability to the
:conditions clause is a side-effect - but an extremely useful one :-)
> By the way my parent child table were just there for illustration. The real
> ones are Lawyer, Matter and Fee. The fees have timestamps and I wanted only
> the fees of a given year (no ages stored here)
Ah...  All is clear.

-- 
Alex