ActiveRecord - how to search by association value?

rubyonrails-talk
2

class Parent < Entity

has_many :children

end

p = Parent.find_by_name(“Michael”)

p.children # Returns all children of the parent

HTH

3

Erol,

Thank you for the reply.

This will work, but is there a way to do this search without adding another association? I am just trying to learn the capabilities of ActiveRecord.

Let me re-state the problem: I either already have the parent object, or know enough of it's attributes to find the parent. But the goal is to find the child, using only its 'parent' association.

Child.find (:name=>"Timmy", parent => knownParent ) - or - Child.find (:name=>"Timmy", parent.name => "Michael")

4

You can use dynamic finders:

Child.find_by_parent_id_and_name(parent.id, “Timmy”)

But then again, if you already have the parent object, the common practice is to setup the children association and get the child using it:

parent.children.find_by_name(“Timmy”)

Which IMO is more readable than the first example.

5

Erol,

Thanks, it did not occur to me to try this kind of finder. The second option also works, especially "common practice" part - learning Rails idioms here.

I initially assumed ActiveRecord would be able to build a query based on known PK and FK attributes of the association without explicit reference of parent's id, which would be, in my opinion, more OO

Nikolai