Unique
The unique constraint takes all resources (within the filter if provided) together and checks if each of them has some value that is unique compared to the same value of all the other resources.
# unique - compares a specific fhirpath expression against all resources and reports duplicates.
- action: unique
status: Testing if all canonicals are unique
filter: StructureDefinition
unique: url
The action here is optional because it's implicitly given by the unique property.
So the minimal set of the above example would be:
- filter: StructureDefinition
unique: url