In order to reliably enforce name uniqueness within a folder, low-level infrastructure is needed. The Nuxeo Shared State Manager NXP-14553 appears to be Nuxeo's long-term solution to address this issue. In the mean time, we have developed a custom unicity-folder marketplace add-on that defines a new UnicityFolder type that enforces name uniqueness for its children. This add-on introduces database-specific SQL uniqueness constraints on the hierarchy table to support reliable enforcement of name uniqueness. Would you be interested in such an add-on?

The solution is to create an EventListenr that on the documentCreated Event check if the name is not already used. If it's used you can throw RecoverableClientException in the listener which will show an error message in the UI