Appearance
If your Omeka S item set is not behaving, the cause is almost always one of three things: a visibility mismatch, a site block that queries the wrong set, or items that were never actually assigned. Item sets are flat groupings of items, so most "missing items" problems come from membership or public/non-public flags rather than from the set itself. Work through visibility, membership and the query in that order and you will fix the large majority of cases in minutes.
Why don't my item set's items show on the public site?
Three checks, in order:
- Item set visibility — open the item set and confirm it is marked Public, not Private.
- Item visibility — individual items have their own public flag; a public set can still contain private items.
- The site block query — the browse-preview or item-showcase block must actually query
item_set_idfor that set.
A common trap: you set the item set public but forgot the items themselves default to your account's visibility. Batch-edit the items to Public to fix it in one pass.
How do I assign many items to a set at once?
Hand-editing each item does not scale. Use batch edit:
- Go to Items, filter to the items you want (by resource template, by search, or tick them manually).
- Choose Edit from the batch actions menu.
- Under Item sets, add the target set and save.
Via the REST API, the same assignment looks like:
bash
curl -X PATCH "https://your-omeka/api/items/4521?key_identity=ID&key_credential=CRED" \
-H "Content-Type: application/json" \
-d '{"o:item_set":[{"o:id":12}]}'The o:item_set array replaces membership, so include every set the item should belong to, not just the new one, or you will silently remove it from others.
Can an item live in several item sets at once?
Yes, and it should when themes overlap. A photograph can belong to "Maritime Collection", "1907 Acquisitions" and "On Display 2025" simultaneously. Item sets are non-exclusive collections, not mutually exclusive folders. If you find yourself duplicating items to put them in two places, stop: assign one item to both sets instead.
How do I diagnose set vs template confusion?
These are different mechanisms people routinely mix up:
| Concept | Controls | Example |
|---|---|---|
| Item set | Grouping / collection membership | "Glass plate negatives" |
| Resource template | Which fields the item shows | "Photograph" with Date, Photographer |
| Site | Public presentation querying sets | The exhibition website |
If items appear but have the wrong fields, that is a template problem, not an item-set problem. If items are grouped wrongly, fix membership.
Why can't I delete or reorder my item set?
Deleting an item set never deletes its items; it only removes the grouping. If the delete button is missing, you lack the permission, or you are not the owner and your role cannot edit it. For ordering, remember item sets do not store a manual sequence. Order is applied at display time by the query:
text
?item_set_id=12&sort_by=dcterms:date&sort_order=ascChange sort_by and sort_order on the page block to reorder what visitors see.
What is a clean item-set strategy that avoids these problems?
- Decide your top-level sets before bulk import, so CSV rows can name them on ingest.
- Use sets for durable groupings (provenance, format, project) and tags or subjects for transient themes.
- Keep set names short and unambiguous; they appear in navigation.
- Audit visibility after every bulk import, because imported items often default to private.
Key Takeaways
- Most "missing items" bugs are visibility or query problems, not item-set faults.
- Items have their own public flag independent of the set; check both.
- An item can belong to many sets at once; never duplicate items to file them twice.
- Use batch edit or the API's
o:item_setarray for bulk assignment, but note the array replaces membership. - Item sets group; resource templates describe; do not confuse the two.
- Ordering is a display-time query parameter, not a stored sequence on the set.
Frequently Asked Questions
Why are my item set's items not appearing on the public site?
Either the item set or its items are marked non-public, or the site's browse-preview block does not query that item set. Check both the resource visibility toggle and the block query.
Can an item belong to more than one item set in Omeka S?
Yes. Items can be assigned to multiple item sets simultaneously, which is the intended way to model overlapping themes, collections and provenance groupings.
How do I add many items to an item set at once?
Use the batch-edit action: filter or select items on the Items browse page, choose Edit, and add the target item set under the Item sets field, which applies to every selected item.
Why can't I delete an item set?
Item sets can be deleted even when they contain items, but you may lack the permission, or a site relies on it. Removing the set does not delete its items; they simply lose that membership.
What is the difference between an item set and a resource template?
An item set is a grouping of items, like a collection; a resource template defines which metadata fields an item exposes. One controls organisation, the other controls description.
How do I sort items within a set?
Sorting is controlled at display time by the site page block or the browse query parameters such as sort_by and sort_order, not by a fixed order stored on the item set itself.