Raise exception if document is not a version

src/caselawclient/errors.py

@@ -89,3 +89,8 @@ class NotSupportedOnVersion(MarklogicAPIError):
     # This error does not come from Marklogic, but is an error raised by this API...
     status_code = 400
     default_message = "An operation was attempted on a version of a document which cannot occur on a version."
+
+
+class OnlySupportedOnVersion(MarklogicAPIError):
+    status_code = 400
+    default_message = "The operation requested cannot be performed on a document that is not a version."

src/caselawclient/models/documents.py

@@ -9,7 +9,11 @@
 
 from caselawclient.models.utilities import extract_version
 
-from ..errors import DocumentNotFoundError, NotSupportedOnVersion
+from ..errors import (
+    DocumentNotFoundError,
+    NotSupportedOnVersion,
+    OnlySupportedOnVersion,
+)
 from ..xml_helpers import get_xpath_match_string, get_xpath_match_strings
 from .utilities import VersionsDict, get_judgment_root, render_versions
 from .utilities.aws import (
@@ -261,13 +265,21 @@ def versions_as_documents(self) -> list[Any]:
 
     @cached_property
     def version_number(self) -> int:
-        "Zero if the version is current, otherwise the highest number is the most recent version"
-        return extract_version(self.uri)
+        """
+        Note that the highest number is the most recent version.
+        Raises an exception if it is not a version (e.g. /2022/eat/1 is not a version)
+        """
+        version = extract_version(self.uri)
+        if version == 0:
+            raise OnlySupportedOnVersion(
+                f"Version number requested for {self.uri} which is not a version"
+            )
+        return version
 
     @cached_property
     def is_version(self) -> bool:
         "Is this document a potentially historic version of a document, or is it the main document itself?"
-        return self.version_number != 0
+        return extract_version(self.uri) != 0
 
     @cached_property
     def content_as_xml(self) -> str:

tests/models/test_documents.py

@@ -5,7 +5,11 @@
 from lxml import etree
 
 from caselawclient.Client import MarklogicApiClient
-from caselawclient.errors import DocumentNotFoundError, NotSupportedOnVersion
+from caselawclient.errors import (
+    DocumentNotFoundError,
+    NotSupportedOnVersion,
+    OnlySupportedOnVersion,
+)
 from caselawclient.models.documents import (
     DOCUMENT_STATUS_HOLD,
     DOCUMENT_STATUS_IN_PROGRESS,
@@ -186,7 +190,8 @@ def test_document_versions_happy_case(self, mock_api_client):
 
     def test_document_version_number_when_not_version(self, mock_api_client):
         base_document = Document("test/1234", mock_api_client)
-        assert base_document.version_number == 0
+        with pytest.raises(OnlySupportedOnVersion):
+            base_document.version_number
         assert not base_document.is_version
 
     def test_document_version_number_when_is_version(self, mock_api_client):