**[BUG FIX] Custom Form Generation – Base XNAT Datatype dropdown empty**

[KRANTHI THEJ]

Hi XNAT community,

We recently encountered an issue where the **Base XNAT Datatype dropdown in the Custom Form Generation wizard was empty** (showing "No choices to choose from"). After extensive debugging, we identified the root cause and a working fix. Sharing here in case others hit the same problem.

---

**Environment**
- XNAT version: 1.9.3.2 (build 681)
- Deployed via Docker (xnat-docker-compose)

---

**Root Cause**

The Custom Form wizard populates the datatype dropdown via `datatypeManager.js`, which calls the REST endpoint:
```
/xapi/role/displays/createable
```
On our instance, this endpoint was returning an error (`Invalid username and/or password`) despite valid credentials and correct user roles. The endpoint appeared registered in Swagger (`/xapi/v2/api-docs`) but failed at runtime — no exception was logged, and all other `/xapi/role/` endpoints (e.g. `/xapi/role/projects`) worked fine.

---

**Fix**

We modified `datatypeManager.js` to use the standard `/REST/search/elements` endpoint instead, which returns the same datatype information and works reliably.

File location inside the container:
```
/usr/local/tomcat/webapps/ROOT/scripts/xnat/app/formJson/datatypeManager.js
```

Changes made:
- Replaced the URL from `xapi/role/displays/createable` to `REST/search/elements?format=json&accessible=true`
- Updated the data mapping to read `ELEMENT_NAME` → `value` and `SINGULAR` → `label` from the new response format (nested under `ResultSet.Result`)
- Added a filter to exclude `template:sample` (a stale datatype that may exist on some instances)

To make the fix persist across container rebuilds, we mounted the modified file as a Docker volume in `docker-compose.yml`:
```yaml
volumes:
  - ./xnat/datatypeManager.js:/usr/local/tomcat/webapps/ROOT/scripts/xnat/app/formJson/datatypeManager.js
```

---

**Questions for the XNAT team**

- Is `/xapi/role/displays/createable` known to have authentication issues in 1.9.3.2?
- Is there a planned fix in a future release?
- Would it make sense to fall back to `/REST/search/elements` if the primary endpoint fails?

Happy to share the full modified `datatypeManager.js` if useful.

Thanks,
Kranthi Thej Kandula
Euro-BioImaging/ CNR / University of Turin