empty fetch result in Nodes

3 files changed, 97 insertions, 30 deletions

diff --git a/bsfs/graph/nodes.py b/bsfs/graph/nodes.py
index 91cbb5d..c6bd5d8 100644
--- a/bsfs/graph/nodes.py
+++ b/bsfs/graph/nodes.py
@@ -249,32 +249,38 @@ class Nodes():
         # add access controls to fetch
         fetch = self._ac.fetch_read(self.node_type, fetch)
 
-        # compose filter ast
-        filter = ast.filter.IsIn(self.guids) # pylint: disable=redefined-builtin
-        # add access controls to filter
-        filter = self._ac.filter_read(self.node_type, filter)
-
-        # validate queries
-        validate.Filter(self._backend.schema)(self.node_type, filter)
-        validate.Fetch(self._backend.schema)(self.node_type, fetch)
-
-        # process results, convert if need be
-        def triple_iter():
-            # query the backend
-            triples = self._backend.fetch(self.node_type, filter, fetch)
-            # process triples
-            for root, name, raw in triples:
-                # get node
-                node = Nodes(self._backend, self._ac, self.node_type, {root})
-                # get path
-                path, tail = name2path[name]
-                # covert raw to value
-                if isinstance(tail.range, bsc.Node):
-                    value = Nodes(self._backend, self._ac, tail.range, {raw})
-                else:
-                    value = raw
-                # emit triple
-                yield node, path, value
+        if len(self._guids) == 0:
+            # shortcut: no need to query; no triples
+            # FIXME: if the Fetch query can given by the user, we might want to check its validity
+            def triple_iter():
+                return []
+        else:
+            # compose filter ast
+            filter = ast.filter.IsIn(self.guids) # pylint: disable=redefined-builtin
+            # add access controls to filter
+            filter = self._ac.filter_read(self.node_type, filter) # type: ignore [assignment]
+
+            # validate queries
+            validate.Filter(self._backend.schema)(self.node_type, filter)
+            validate.Fetch(self._backend.schema)(self.node_type, fetch)
+
+            # process results, convert if need be
+            def triple_iter():
+                # query the backend
+                triples = self._backend.fetch(self.node_type, filter, fetch)
+                # process triples
+                for root, name, raw in triples:
+                    # get node
+                    node = Nodes(self._backend, self._ac, self.node_type, {root})
+                    # get path
+                    path, tail = name2path[name]
+                    # covert raw to value
+                    if isinstance(tail.range, bsc.Node):
+                        value = Nodes(self._backend, self._ac, tail.range, {raw})
+                    else:
+                        value = raw
+                    # emit triple
+                    yield node, path, value
 
         # simplify by default
         view_kwargs['node'] = view_kwargs.get('node', len(self._guids) != 1)
diff --git a/test/graph/ac/test_null.py b/test/graph/ac/test_null.py
index 544a01e..6053f81 100644
--- a/test/graph/ac/test_null.py
+++ b/test/graph/ac/test_null.py
@@ -136,6 +136,15 @@ class TestNullAC(unittest.TestCase):
         # query can be none
         self.assertIsNone(ac.filter_read(self.ent_type, None))
 
+    def test_fetch_read(self):
+        query = ast.fetch.All(
+            ast.fetch.Fetch(ns.bse.tag, ast.fetch.Value(ns.bse.label, 'tag_label')),
+            ast.fetch.Node(ns.bse.tag, 'tag_node'),
+            ast.fetch.Value(ns.bse.iso, 'iso'))
+        ac = NullAC(self.backend, self.user)
+        # NullAC returns query
+        self.assertEqual(query, ac.fetch_read(self.ent_type, query))
+
 
 ## main ##
 
diff --git a/test/graph/test_nodes.py b/test/graph/test_nodes.py
index 9541656..bf73e6e 100644
--- a/test/graph/test_nodes.py
+++ b/test/graph/test_nodes.py
@@ -346,6 +346,10 @@ class TestNodes(unittest.TestCase):
             Nodes(self.backend, self.ac, self.user_type, {URI('http://example.com/me/user#1234'), URI('http://example.com/me/user#4321')}))
         self.assertSetEqual(curr, set(self.backend._graph))
 
+        # can set on empty nodes
+        nodes = Nodes(self.backend, self.ac, self.ent_type, {})
+        self.assertEqual(nodes, nodes.set(self.p_filesize.uri, 1234))
+
 
     def test_set_from_iterable(self):
         self.assertSetEqual(set(self.backend._graph), self.schema_triples | set())
@@ -388,6 +392,11 @@ class TestNodes(unittest.TestCase):
             (self.p_author.uri, Nodes(self.backend, self.ac, self.user_type, {URI('http://example.com/me/user#1234'), URI('http://example.com/me/user#4321')}))))
         self.assertSetEqual(curr, set(self.backend._graph))
 
+        # can set on empty nodes
+        nodes = Nodes(self.backend, self.ac, self.ent_type, {})
+        self.assertEqual(nodes, nodes.set_from_iterable([(self.p_filesize.uri, 1234)]))
+
+
     def test_get(self):
         # setup: add some instances
         Nodes(self.backend, self.ac, self.ent_type, {'http://example.com/me/entity#1234'}) \
@@ -403,6 +412,7 @@ class TestNodes(unittest.TestCase):
             .set(bst.label, 'tag_label_4321')
         # setup: get nodes instance
         nodes = Nodes(self.backend, self.ac, self.ent_type, self.ent_ids)
+
         # must pass at least one path
         self.assertRaises(AttributeError, nodes.get)
         # view must be list or dict
@@ -467,10 +477,52 @@ class TestNodes(unittest.TestCase):
             Nodes(self.backend, self.ac, self.ent_type, {'http://example.com/me/entity#1234'}): {'hello world'},
             })
 
-        # FIXME: What if I call `get` with a single predicate and a single node, but
-        # that node has no value for that predicate?
-        # so, essentially, what if triples is empty? -> Also check in test_result!
-        raise NotImplementedError()
+        # results can be empty
+        nodes = Nodes(self.backend, self.ac, self.ent_type, {'http://example.com/me/entity#4321'}) # has filesize, tag but no comment
+        # unique paths return the default value
+        self.assertIsNone(nodes.get(ns.bse.author))
+        self.assertEqual(nodes.get(ns.bse.author, default=1234), 1234)
+        # non-unique paths return an empty set
+        self.assertSetEqual(nodes.get(ns.bse.comment), set())
+
+        # nodes can have no guids
+        nodes = Nodes(self.backend, self.ac, self.ent_type, set())
+        # empty nodes does not excuse an invalid request
+        self.assertRaises(TypeError, nodes.get, 1234)
+        self.assertRaises(errors.ConsistencyError, nodes.get, ns.bse.invalid)
+        # list view always returns an empty list
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, node=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, path=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, node=True, path=True, value=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, node=False)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, path=False)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, view=list, node=False, path=False, value=False)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, node=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, path=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, node=True, path=True, value=True)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, node=False)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, path=False)), [])
+        self.assertListEqual(list(nodes.get(ns.bse.comment, ns.bse.filesize, view=list, node=False, path=False, value=False)), [])
+        # dict view returns an empty dict or an empty set
+        self.assertDictEqual(nodes.get(ns.bse.comment, view=dict), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, view=dict, node=True), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, view=dict, path=True), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, view=dict, node=True, path=True, value=True, default=None), {})
+        self.assertSetEqual(nodes.get(ns.bse.comment, view=dict, node=False), set())
+        self.assertDictEqual(nodes.get(ns.bse.comment, view=dict, path=False), {})
+        self.assertSetEqual(nodes.get(ns.bse.comment, view=dict, node=False, path=False), set())
+        self.assertSetEqual(nodes.get(ns.bse.comment, view=dict, node=False, path=False, value=False, default=None), set())
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, node=True), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, path=True), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, node=True, path=True, value=True, default=None), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, node=False), {})
+        self.assertDictEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, path=False), {})
+        self.assertSetEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, node=False, path=False), set())
+        self.assertSetEqual(nodes.get(ns.bse.comment, ns.bse.filesize, view=dict, node=False, path=False, value=False, default=None), set())
+
 
     def test_getattr(self):
         nodes = Nodes(self.backend, self.ac, self.ent_type, {'http://example.com/me/entity#1234'})