Filtering child objects in a has_many :through relationship in Rails 3

An even cleaner way would be to add an association to your Company model, something like this:

has_many :admins, :through => :company_memberships, :class_name => :user, :conditions => {:admin => true}

You might have to dig into the rails doc to get the exact syntax right.

You shouldn't need :include, unless you have other classes associated with :user that you might reference in your view.

I believe I was going about this the wrong way, specifying conditions on company_memberships instead of users, which was what I actually wanted (a list of Users, not a list of CompanyMemberships). The solution I think I was looking for is:

users.where(:company_memberships => {:admin => true})

which generates the following SQL (for company with ID of 1):

SELECT "users".* FROM "users"
  INNER JOIN "company_memberships"
    ON "users".id = "company_memberships".user_id
  WHERE (("company_memberships".company_id = 1))
    AND ("company_memberships"."admin" = 't')

I'm not sure yet if I'll need it, but the includes() method will perform eager loading to keep down the number of SQL queries if necessary:

Active Record lets you specify in advance all the associations that are going to be loaded. This is possible by specifying the includes method of the Model.find call. With includes, Active Record ensures that all of the specified associations are loaded using the minimum possible number of queries.queries. ^{RoR Guides: ActiveRecord Querying}

(I'm still open to any suggestions from anyone who thinks this isn't the best/most effective/right way to go about this.)

How about something like this:

Company.find(:id).company_memberships.where(:admin => true).joins(:user)