Rails Ruby on Rails → 3.0.6

This commit appears to have (unintentionally?) removed some caching that was being done for table columns when a has_one (possibly other types as well) association has conditions and is eager loaded.

I am running into a situation where several hundred rows are being selected, with an eager loaded has_one that has conditions. The columns for the associated table are being queried (at least) once for each result row. This did not happen in v3.0.4. And it makes the query unacceptably slow.

It appears that when eager loading a has_one association an AssociationProxy instance is created for each result record, and its @finder_sql instance variable is populated in its constructor. If the association has conditions they need to be sanitized against the columns for the table being associated with.

The commit linked above introduces a new, preferred way of specifying interpolated conditions on associations (using a proc). In doing so the sanitized_conditions method of the MacroReflection class is no longer being used, and that is where the caching used to take place.

From the AssociationProxy class in v3.0.4:

def conditions
  @conditions ||= interpolate_sql(@reflection.sanitized_conditions) if @reflection.sanitized_conditions
end

And here it is in 3.0.5 (no longer using sanitized_conditions):

def conditions
  @conditions ||= @reflection.options[:conditions] && interpolate_and_sanitize_sql(@reflection.options[:conditions])
end

The problem can be seen in a test by adding a has_one with conditions to the test model Post class (the following test stuff is also attached as a patch against the 3-0-stable branch):

has_one :first_post_comment, :class_name => 'Comment', :conditions => {:body => 'First Post!'}

In order to track the column lookups for a specific table I modified the column_with_calls code in test/cases/helper.rb:

ActiveRecord::Base.connection.class.class_eval {
  attr_accessor :column_calls, :column_calls_by_table

  def columns_with_calls(*args)
    @column_calls ||= 0
    @column_calls_by_table ||= Hash.new {|h,table| h[table] = 0}

    @column_calls += 1
    @column_calls_by_table[args.first.to_s] += 1
    columns_without_calls(*args)
  end

  alias_method_chain :columns, :calls
}

And finally a test added to test/cases/associations/eager_test.rb. This test passes in 3.0.4 and fails in 3.0.5:

def test_preload_has_one_with_conditions
  # pre-heat our cache
  Post.arel_table.columns
  Comment.columns

  Post.connection.column_calls_by_table['comments'] = 0
  Post.includes(:very_special_comment).all.to_a
  assert_equal 0, Post.connection.column_calls_by_table['comments']

  Post.connection.column_calls_by_table['comments'] = 0
  Post.includes(:first_post_comment).all.to_a
  assert_equal 1, Post.connection.column_calls_by_table['comments']
end

I have not worked out a fix for this yet.