Also restoring an access_url column to registry result's to_table.

Again, that's strictly for backward compatiblity.

pyvo/registry/regtap.py

@@ -199,20 +199,27 @@ def get_summary(self):
 
         This is mainly intended for interactive use, where people would
         like to inspect the matches in, perhaps, notebooks.
+
+        This returns a column access_url for backwards compatibilty.  Do
+        not use what you find there in new code.  Use get_service on the
+        records themselves instead.
         """
         return table.Table([
                 list(range(len(self))),
                 [r.short_name for r in self],
                 [r.res_title for r in self],
                 [r.res_description for r in self],
-                [", ".join(sorted(r.access_modes())) for r in self]],
-            names=("index", "short_name", "title", "description", "interfaces"),
+                [", ".join(sorted(r.access_modes())) for r in self],
+                [r.get_unique_access_url() for r in self]],
+            names=("index", "short_name", "title", "description",
+                "interfaces", "access_url"),
             descriptions=(
                 "Index to access the resource within self",
                 "Short name",
                 "Resource title",
                 "Resource description",
-                "Access modes offered"))
+                "Access modes offered",
+                "Unique access URL (or None for multi-interface records)"))
 
     @functools.lru_cache(maxsize=None)
     def _get_ivo_index(self):
@@ -534,6 +541,19 @@ def access_url(self):
                 " may change in the future."))
         return access_urls[0]
 
+    def get_unique_access_url(self):
+        """
+        return the access URL of this resource in case it is uniquely
+        defined.
+
+        This is for legacy code that assumes there is just one
+        access URL.  It will return None if Resource has zero or more than
+        one interfaces.
+        """
+        access_urls = list(sorted(set(self["access_urls"])))
+        if len(access_urls)==1:
+            return access_urls[0]
+
     @property
     def standard_id(self):
         """

pyvo/registry/tests/test_regtap.py

@@ -316,13 +316,15 @@ def test_to_table(multi_interface_fixture, capabilities):
     t = regtap.search(
         ivoid="ivo://org.gavo.dc/flashheros/q/ssa").get_summary()
     assert (set(t.columns.keys())
-        == {'index', 'short_name', 'title', 'description', 'interfaces'})
+        == {'index', 'short_name', 'title', 'description', 
+            'interfaces', 'access_url'})
     assert t["index"][0] == 0
     assert t["title"][0] == 'Flash/Heros SSAP'
     assert (t["description"][0][:40]
         == 'Spectra from the Flash and Heros Echelle')
     assert (t["interfaces"][0]
         == 'datalink#links-1.0, soda#sync-1.0, ssa, tap#aux, web')
+    assert (t["access_url"][0] is None)
 
 
 @pytest.fixture()