limitations of :finder_sql

Question

In a rails app, I using the :finder_sql option in a has_many declaration. The rails docs say that when I do this, "find_in_collection is not added." What does this mean?

Answer 1

it means that when you have a has_many relationship between to tables like:

person has_many :books, :finder_sql

you wont get the person.books.find* methods you normaly would have gotten. the reason for this behavior is that activerecord cant easily compose the finder_sql with the find* methods you would be using, so it cant really give you that functionality

Answer 2

This means that it doesn't support the method for finding an instance within a collection. The docs call it find_in_collection (where "collection" is whatever the name of your association). An example might be more helpful here:

class Author < ActiveRecord::Base
  has_many :posts

  has_many :special_posts, :class_name => "Post", 
           :finder_sql => "SELECT * FROM posts WHERE ..."
end

author.find_in_posts(30)          # it finds and returns post 30
author.find_in_special_posts(30)  # not supported because finder_sql is used here.