Merge pull request #613 from d-giles/getdatalink-328-2

Getdatalink - guess or return more informative error

CHANGES.rst

@@ -38,6 +38,8 @@ Enhancements and Fixes
 
 - New sub-package discover for global dataset discovery. [#470]
 
+- Updated getdatalink to be consistent with iter_datalinks. [#613]
+
 
 Deprecations and Removals
 -------------------------

pyvo/dal/adhoc.py

@@ -263,6 +263,15 @@ def _guess_access_url(row):
         if access_url:
             return access_url
 
+    @staticmethod
+    def _guess_datalink(row, **kwargs):
+        # TODO: we should be more careful about whitespace, case
+        # and perhaps more parameters in the following comparison
+        if row._results._guess_access_format(row) == DATALINK_MIME_TYPE:
+            access_url = row._results._guess_access_url(row)
+            if access_url is not None:
+                return DatalinkResults.from_result_url(access_url, **kwargs)
+
     def _iter_datalinks_from_product_rows(self):
         """yield datalinks from self's rows if they describe datalink-valued
         products.
@@ -309,13 +318,31 @@ class DatalinkRecordMixin:
     """
 
     def getdatalink(self):
+        """
+        Retrieve the datalink information for this record.
+
+        Returns
+        -------
+        DatalinkResults
+            The datalink results for this record.
+
+        Raises
+        ------
+        DALServiceError
+            If no datalink information is found for this record.
+        """
         try:
             datalink = self._results.get_adhocservice_by_ivoid(DATALINK_IVOID)
 
             query = DatalinkQuery.from_resource(self, datalink, session=self._session)
             return query.execute()
-        except DALServiceError:
-            return DatalinkResults.from_result_url(self.getdataurl(), session=self._session)
+        except DALServiceError as error:
+            datalink = self._results._guess_datalink(self, session=self._session)
+            if datalink is not None:
+                return datalink
+            else:
+                # re-raise the original error if nothing works
+                raise DALServiceError("No datalink found for record.") from error
 
     @stream_decode_content
     def getdataset(self, timeout=None):

pyvo/dal/tests/test_datalink.py

@@ -4,14 +4,16 @@
 Tests for pyvo.dal.datalink
 """
 from functools import partial
+import re
 
 import pytest
 
 import pyvo as vo
-from pyvo.dal.adhoc import DatalinkResults
+from pyvo.dal.adhoc import DatalinkResults, DALServiceError
 from pyvo.dal.sia2 import SIA2Results
 from pyvo.dal.tap import TAPResults
 from pyvo.utils import testing, vocabularies
+from pyvo.dal.sia import search
 
 from astropy.utils.data import get_pkg_data_contents, get_pkg_data_filename
 
@@ -30,6 +32,27 @@ def callback(request, context):
         yield matcher
 
 
+sia_re = re.compile("http://example.com/sia.*")
+
+
+@pytest.fixture()
+def register_mocks(mocker):
+    with mocker.register_uri(
+        "GET",
+        "http://example.com/querydata/image.fits",
+        content=get_pkg_data_contents("data/querydata/image.fits"),
+    ) as matcher:
+        yield matcher
+
+
+@pytest.fixture()
+def sia(mocker):
+    with mocker.register_uri(
+        "GET", sia_re, content=get_pkg_data_contents("data/sia/dataset.xml")
+    ) as matcher:
+        yield matcher
+
+
 @pytest.fixture()
 def datalink(mocker):
     def callback(request, context):
@@ -307,3 +330,14 @@ def test_generic_record(self):
         assert len(links) == 1
         assert (next(links[0].bysemantics("#this"))["access_url"]
             == "http://dc.zah.uni-heidelberg.de/getproduct/flashheros/data/ca90/f0011.mt")
+
+
+@pytest.mark.usefixtures("sia", "register_mocks")
+@pytest.mark.filterwarnings("ignore::astropy.io.votable.exceptions.W06")
+def test_no_datalink():
+    # for issue #328 getdatalink() exits messily when there isn't a datalink
+
+    results = search("http://example.com/sia", pos=(288, 15), format="all")
+    result = results[0]
+    with pytest.raises(DALServiceError, match="No datalink found for record."):
+        result.getdatalink()