I have no idea why mongoid started to acting strange. This is the second issue I am filing.

I have a model:

class SpannedLineItem
    belongs_to :master_line_item, class_name => 'LineItem'
end

class LineItem
  belongs_to :spanned, :class_name => 'SpannedLineItem'
end

My code in the controller looks like this:

@line_item = LineItem.find(params[:id])

if(@line_item.spanned)
   @line_item = @line_item.spanned.master_line_item
end

Basically if the line item is spanned I am interested in another - master - line item.

The problem is, @line_item in the end will equal the non master item...
I checked the database, mongoid does look up the fields, but does not continue to look for the line item pointed by master_line_item_id
MONGODB finance_rails2_development['line_items'].find({:_id=>BSON::ObjectId('4e57f61bb9fdd9121b000600')})
MONGODB finance_rails2_development['spanned_line_items'].find({:_id=>BSON::ObjectId('4e57f61bb9fdd9121b0005fe')})

Modifying the controller to this:
if(@line_item.spanned)
@line_item = LineItem.find(@line_item.spanned.master_line_item_id)
end

Does work and the log shows three finds:
MONGODB finance_rails2_development['line_items'].find({:_id=>BSON::ObjectId('4e57f61bb9fdd9121b000600')})
MONGODB finance_rails2_development['spanned_line_items'].find({:_id=>BSON::ObjectId('4e57f61bb9fdd9121b0005fe')})
MONGODB finance_rails2_development['line_items'].find({:_id=>BSON::ObjectId('4e57f61bb9fdd9121b0005fd')})

I am using 2.1.9