HASONEFILTER Returns TRUE when the number of directly filtered values on columnName is one; otherwise returns FALSE.
Syntax
HASONEFILTER(columnName)
Parameters
ColumnName – The name of an existing column, using standard DAX syntax. It cannot be an expression.
Return Value
TRUE when the number of directly filtered values on columnName is one; otherwise returns FALSE.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference