attribute name is optional only for cohort attribte level

Author: Karthikeyannhs

src/eligibility_signposting_api/model/campaign_config.py

@@ -163,6 +163,17 @@ def parse_yn_to_bool(cls, v: str | bool) -> bool:  # noqa: N805
             return v.upper() == "Y"
         return v
 
+    @model_validator( mode="after")
+    def validate_attribute_name_is_optional_only_for_cohort_attribute_level(self)  -> typing.Self:  # noqa: N805
+        if self.attribute_name:
+            return self
+        else:
+            if self.attribute_level == RuleAttributeLevel.COHORT:
+                return self
+            else:
+                raise ValueError(f"AttributeName must be set for {self.attribute_level} AttributeLevel.")
+
+
     _parent: Iteration | None = PrivateAttr(default=None)
 
     def set_parent(self, parent: Iteration) -> None: