Relative datasource for template field

Question

I have created a branch template [Comparison Chart] which contains a folder item called [Headers] which is designed to contain items of the template [CChart Header].

Inside the [Comparison Chart] item, on the same level as the headers folder will be items of [CChart Row] template which has a droplist field called [Selected Headers]. I would like the [Selected Headers] field to be populated with any/all items inside the [Headers] folder, but I do not know how to setup the field to have a relative datasource.

Here's a visual representation of the tree structure:

Comparison Chart ([Comparison Chart] item)
     Headers (folder)
          Blue ([CChart Header] item)
          Red ([CChart Header] item)
          Green ([CChart Header] item)
     Volkswagons ([CChart Row] item)
     Fords ([CChart Row] item)
     Toyotas ([CChart Row] item)

Eventually, I will spit out a table similar to the below, but I can't figure out how to set the datasource so that authors can select which headers apply to which rows:

The manufacturers produce cars in the colors indicated below
               Blue     Red     Green
Volkswagons     X        X        X
Fords                    X
Toyotas         X                 X

Answer 1

[CChart Row] template would have Multilist field instead of Droplist as you want to select multiple [CChart Hearder] items like blue, red green while Droplist will allow to select only one of these.

Reg datasource query, you can use any of the below

1. query:../Headers/*
2. query:./ancestor::* [@@name=‘Comparison Chart]/Headers/*

Answer 2

You can use something like this in your template field source (You would need to change the templateid value to be the actual ID of your comparison chart template ID ):

query:./ancestor-or-self::*[@@templateid='{Comparison Chart Template ID}']/Headers/*

Or another way using the parent folder name

query:./ancestor-or-self::*[@@name='Comparison Chart']/Headers/*