Closes #6138: Add an 'empty' filter modifier for character fields

netbox/extras/lookups.py

@@ -0,0 +1,17 @@
+from django.db.models import CharField, Lookup
+
+
+class Empty(Lookup):
+    """
+    Filter on whether a string is empty.
+    """
+    lookup_name = 'empty'
+
+    def as_sql(self, qn, connection):
+        lhs, lhs_params = self.process_lhs(qn, connection)
+        rhs, rhs_params = self.process_rhs(qn, connection)
+        params = lhs_params + rhs_params
+        return 'CAST(LENGTH(%s) AS BOOLEAN) != %s' % (lhs, rhs), params
+
+
+CharField.register_lookup(Empty)