Collection Tree Select

An Omeka Classic plugin, and a companion to Collection Tree. It turns the flat Collection dropdowns into a searchable tree picker, colour-codes every collection by the top-level collection it belongs to, and applies the same colours to Collection Tree's own tree page.

Collection Tree is left completely untouched, so it survives its own upgrades.

Why

A native <select> cannot nest. <optgroup> gives exactly one level and its labels are not selectable, which is wrong for Omeka, where a parent collection is a real collection you may want to assign items to. The only way to get arbitrary depth with every level still choosable is to keep the native <select> as the form value and render the tree over it.

Requirements

Omeka Classic 2.0+ (developed and tested against 3.2.1)
The Collection Tree plugin, 2.1 or 2.2, installed and active

Install

Download the ZIP from Releases and unpack it into your Omeka plugins/ directory, so you have plugins/CollectionTreeSelect/.
Install and activate it under Settings → Plugins. Collection Tree must be active first; it is declared as a required plugin.

What it changes

Where	What happens
Item Add / Edit → Collection	Tree picker
Item Batch Edit → Collection	Tree picker, and the options are re-sorted into tree order
Collection Edit → Parent Collection	Tree picker over Collection Tree's own select
Advanced search → Search By Collection	Tree picker, plus the subcollections Collection Tree strips out on the public side
Collection Tree page, and the tree on a collection's page	Rows tinted to match the dropdowns

Without JavaScript the dropdowns stay native and fall back to non-breaking-space indentation.

Configuration

Settings → Plugins → Collection Tree Select → Configure

Setting	Default	Effect
Enable tree picker	on	Off leaves dropdowns native, indentation only
Colour-code trees	on	Tint each collection with its top-level ancestor's colour
Starting colour	210	Hue of the first tree, in degrees: 0 red, 120 green, 210 blue, 300 magenta
Colour intensity	50	Tint strength, 0 barely-there to 100 vivid
Colour the Collection Tree page	on	Extend those colours to the tree page
Full collection list in dropdowns	on	Restore subcollections stripped from public select options
Apply to the public site	off	Extend all of the above to the public theme
Indent per level (px)	18	Indentation in the picker
Show search box from	8	Collections needed before the search field appears; 0 always shows it
Plain-select indent	4	Non-breaking spaces per level in the no-JavaScript fallback

Apply to the public site is off by default because the tree page is re-laid out as full-width rows, which is a visible change to your theme. Turn it on and check the result.

How it works

The collection_trees table is read once per request and emitted as three collection_id-keyed maps — depth, parent and hue. The browser never has to parse label prefixes, though it will as a fallback. Collections orphaned or left in a cycle by a bad import are treated as roots rather than hanging the request.

Indentation is replaced, not added to. Every label is stripped back to the bare collection name and re-padded, in PHP (stripIndent()) and again in JavaScript (PREFIX_RE). Feed it -- Faculty letters and you get one clean Faculty letters at depth 2. There is no need to edit Collection Tree, and you should not.

Filter order matters. Collection Tree registers collections_select_options at the default priority and its implementation ends with array_intersect_key($treeOptions, $options), discarding whatever ran before it. This plugin registers at priority 100 so it always runs last, regardless of which plugin was installed first.

Batch edit is re-sorted in the browser. items/batch-edit-common.php calls findPairsForSelectForm() directly, so no PHP filter can reach it and its subcollections arrive detached from their parents. The script re-sorts them depth-first. Siblings keep their existing order, which makes the pass idempotent on selects that are already correct, so it is applied everywhere.

Colours are stable. Each top-level collection gets a hue, assigned by position among the roots sorted by id, using the base-2 van der Corput sequence. Adding a child or renaming a collection never reshuffles the palette; only adding or removing a top-level collection shifts the roots after it. Spacing is exactly optimal at 2, 4, 8 and 16 roots and no worse than about 62% of optimal in between.

Starting colour rotates that whole wheel, so you can bring the palette toward your site's own colours without losing the spacing. Colour intensity scales saturation and darkness together; the coloured edge stripe keeps its strength at any setting, so trees stay distinguishable even at 0. Both are clamped on save, and 50 reproduces the palette exactly as it shipped before the settings existed.

The tree page is restyled assertively. It belongs to your theme, so the plugin's selectors match on #collection-tree as well as its own class, and the tint is the one declaration marked !important. That is scoped to rows which actually have a colour, so uncoloured rows keep your theme's background. Text on a tinted row is forced to a dark neutral, since the tints are 88–96% light and a theme's pale link text would be unreadable on them.

Advanced search listed only top-level collections

On the public side only, and this is the reason the plugin restores them.

Collection Tree's "browse only root collections" setting hides child collections from the collections browse, via hookCollectionsBrowseSql(). That is aimed at the browse page, but select options are built by findPairsForSelectForm(), which routes through getSelectForFindBy() and fires the very same collections_browse_sql hook. The public advanced search therefore offered root collections only, with no way to search inside a subcollection. The admin side was never affected, because the hook returns early on is_admin_theme().

Collection Tree 2.2 added an opt-out: the hook returns early when the browse params carry collection_tree_all_collections. 2.1 has the rule but no opt-out, so this plugin tries the documented route, checks whether the answer actually came back complete, and if not falls back to building the list from Table_Collection::getSelect() — which applies Omeka's public-permission filtering but, unlike getSelectForFindBy(), never fires the browse hook.

Either way, a visitor sees exactly the collections they were allowed to see before, plus the subcollections among them. Nothing private is exposed.

The restoration is conservative: if any nested collection is still present then nothing was stripped, and the options are left alone — so another plugin narrowing the dropdown for its own reasons is never overridden.

It also puts back the No Collection entry, which the advanced search form requests via include_no_collection and Collection Tree drops.

Extension points

Filter	Receives	Use
`collection_tree_select_selectors`	array of CSS selectors	Enhance a collection select the plugin does not know about
`collection_tree_select_pages`	`module => controller => [actions]`	Register a page carrying such a select
`collection_tree_select_tree_pages`	`module => controller => [actions]`	Register a page rendering `#collection-tree`

The page maps gate asset loading, so a select on an unregistered page is never enhanced however well its selector matches.

Notes

select2 4.0.13 is vendored under views/shared/{javascripts,css}/vendor/. No CDN is contacted. It is MIT licensed — see views/shared/LICENSE.select2.md.
Assets load only on pages that carry a collection dropdown or the tree markup. select2 is ~95KB and is skipped on the tree page, which does not need it.
Omeka calls jQuery.noConflict(), so the script uses jQuery, not $.
Upgrading seeds any newly added settings via hookUpgrade, since _installOptions() only runs on a fresh install.

Development

See test/README.md. Two suites, neither needing an Omeka install: php test/test-tree.php for the server-side logic, and a browser page for the picker, the colours and theme conflicts.

License

GPLv3, matching Collection Tree. See LICENSE.