Overriding find


I am using single table inheritance which looks something like this:

class Employee < ActiveRecord::Base
belongs_to :employee_type
Manager < Employee
Programmer < Employee

When I call Manager.find(…) or Programmer.find(…) regardless of
what parameters are passed to find I only want that employee type to
be returned. So Prgrammers.find(:all) will return all programmers, but
not managers.

I somehow need to inject a condition “member_type = xxx” into every
find query of the Employee subclass.

I would like to be able to do it without any restrictions on calling
find. So find(:first), find(id) and find(:all) will all work.

Has anyone done this before or can point me in the right direction?



Will wrote:

be returned. So Prgrammers.find(:all) will return all programmers, but
not managers.

Google [rails polymorphic association]!



It looks like STI is what you’re using and what you want (assuming
your data lives in one table). Looking at the AWDwRoR book, it
doesn’t seem like you need the belongs_to :employee_type in your
Employee class unless it’s related to something else in your app.
Also, I’m assuming that you have abbreviated your Manager and
Programmer classes and that they actually look like this:

class Manager < Employee

class Programmer < Employee

What does the data in your employees table look like? Do you have a
“type” column that stores either “Manager” or “Programmer” in it? I
haven’t used STI before, but based on the examples that I’ve seen, it
should work as you want it to as long as it’s set up correctly.


What Kyle said. :slight_smile:

create_table :employees do |t|
t.string :type, :default => “Employee”, :null => false
t.string :name
(… other fields …)

Then all you need is the model extensions like Kyle wrote:

class Employee < ActiveRecord::Base; end
class Manager < Employee; end
class Programmer < Employee; end

And you can do stuff like:

managers = Manager.find :all
best_programmers = Programmer.find_all_by_language(“Ruby on Rails”)
all_employees = Employee.find :all


Thanks all for your replies. The type field will sort this out.

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