How do I filter only the root terms in a vocabulary in a view?

Question

I have have a vocabulary structured as so:

• Root Alpha
  • Term Alpha 1
  • Term Alpha 2
    • Subterm Alpha 1
• Root Beta
• Root Gamma
  • Term Gamma 1
  • Term Gamma 2

How do I filter the view to show only the root terms of the vocabulary? Currently my view is displaying the root terms as well as the children (Term * *)

Going forward from that I would like to pass the argument 'Root Alpha' (or its tid, or whatever from a context) and then have it filter to only 'Root Alpha's direct children. (Term Alpha *). Filtering to a depth any further than that would be a bonus.

I can get it to work if I put all my terms in one root term so that the vocab becomes:

• True Root
  • Root Alpha
    • Term Alpha 1
    • Term Alpha 2
      • Subterm Alpha 1
  • Root Beta
  • Root Gamma
    • Term Gamma 1
    • Term Gamma 2

I'm not sure which vocab structure is more correct, writing this made me realise I have some reading to do apart from figuring this out with views.

Answer 1

For displaying only the root terms, I have a solution which surely will make someone facepalm (at least I did that):

1. Add a contextual filter to your taxonomy view

2. Select Taxonomy term: parent term.

   Set it up like this: When a filter value is not available: Provide default value - Fixed value. Set the value to 0.

Yeah, that's all. Terms without parent have 0 here. See the description of the parent field of the taxonomy_term_hierarchy table:

Primary Key: The {taxonomy_term_data}.tid of the term's parent. 0 indicates no parent.

Answer 2

if you have a static taxonomy structure, you can filter using filter criterion: Content: Has taxonomy terms (with depth) then in this place you can select just the root terms to filter:

I hope information be useful.

Answer 3

You can also do it with a simple filter, and a non-static taxonomy structure :

1. Add a filter criterion : Taxonomy term : parent id
2. Select operator "Is equal to" and fill the value with "NULL"

It will display only the root terms of your taxonomy, and will still work if you change the taxonomy structure later...

Answer 4

You can select it with WHERE parent = 0 using db_query() in your page.