MongoDB: read can be return most recent match with last_only

src/metaopt/io/database/__init__.py

@@ -106,7 +106,7 @@ def write(self, collection_name, data,
         pass
 
     @abstractmethod
-    def read(self, collection_name, query, selection=None):
+    def read(self, collection_name, query, selection=None, last_only=False):
         """Read a collection and return a value according to the query.
 
         Parameters
@@ -117,6 +117,8 @@ def read(self, collection_name, query, selection=None):
            Filter entries in collection.
         selection : dict, optional
            Elements of matched entries to return, the projection.
+        last_only : bool, optional
+           If True, return only the most recent entry that matches `query`.
 
         :return: matched document[s]
 

src/metaopt/io/database/mongodb.py

@@ -111,16 +111,20 @@ def write(self, collection_name, data,
                                           upsert=True)
         return result.acknowledged
 
-    def read(self, collection_name, query, selection=None):
+    def read(self, collection_name, query, selection=None, last_only=False):
         """Read a collection and return a value according to the query.
 
         .. seealso:: :meth:`AbstractDB.read` for argument documentation.
 
         """
         dbcollection = self._db[collection_name]
 
-        cursor = dbcollection.find(query, selection)
-        dbdocs = list(cursor)
+        if not last_only:
+            cursor = dbcollection.find(query, selection)
+            dbdocs = list(cursor)
+        else:
+            # Return the most recent of the query
+            dbdocs = list(dbcollection.find(query, selection, sort=[('$natural', -1)], limit=1))
 
         if not dbdocs:
             return None

tests/core/unittests/mongodb_test.py

@@ -106,24 +106,59 @@ def test_read_experiment(self, exp_config, moptdb):
             'experiments', {'exp_name': 'supernaedo2', 'metadata.user': 'tsirif'})
         assert loaded_config == exp_config[0][:2]
 
+        loaded_config = moptdb.read(
+            'experiments', {'exp_name': 'supernaedo2', 'metadata.user': 'tsirif'},
+            last_only=True)
+        assert loaded_config == exp_config[0][1]
+
         loaded_config = moptdb.read('experiments',
                                     {'exp_name': 'supernaedo2',
                                      'metadata.user': 'tsirif',
                                      'metadata.datetime': datetime(2017, 11, 22, 23, 0, 0)})
         assert loaded_config == exp_config[0][0]
 
     def test_read_default(self, exp_config, moptdb):
-        """Fetch value(s) from an entry."""
+        """Fetch value(s) from an entry.
+
+        - ``last_only`` is implicitly False
+        """
         value = moptdb.read(
             'experiments', {'exp_name': 'supernaedo2', 'metadata.user': 'tsirif'},
             selection={'algorithms': 1, '_id': 0})
         assert value == [{'algorithms': exp_config[0][i]['algorithms']} for i in (0, 1)]
 
+    def test_read_last_only_false(self, exp_config, moptdb):
+        """Fetch value(s) from an entry.
+
+        - ``last_only`` is explicitly False
+        """
+        value = moptdb.read(
+            'experiments', {'exp_name': 'supernaedo2', 'metadata.user': 'tsirif'},
+            selection={'algorithms': 1, 'status': 1}, last_only=False)
+        assert value == [{'algorithms': exp_config[0][i]['algorithms'],
+                          'status': exp_config[0][i]['status'],
+                          '_id': exp_config[0][i]['_id']} for i in (0, 1)]
+
+    def test_read_last_only_true(self, exp_config, moptdb):
+        """Fetch value(s) from an entry.
+
+        - ``last_only`` is explicitly False
+        """
+        value = moptdb.read(
+            'experiments', {'exp_name': 'supernaedo2', 'metadata.user': 'tsirif'},
+            selection={'algorithms': 1, '_id': 0}, last_only=True)
+        assert value == {'algorithms': exp_config[0][1]['algorithms']}
+
     def test_read_nothing(self, moptdb):
         """Fetch value(s) from an entry."""
         value = moptdb.read(
             'experiments', {'exp_name': 'not_found', 'metadata.user': 'tsirif'},
-            selection={'algorithms': 1})
+            selection={'algorithms': 1}, last_only=False)
+        assert value is None
+
+        value = moptdb.read(
+            'experiments', {'exp_name': 'not_found', 'metadata.user': 'tsirif'},
+            selection={'algorithms': 1}, last_only=True)
         assert value is None
 
     def test_read_trials(self, exp_config, moptdb):