Improve performance of get_conceptscheme. Refs #71 (#72)

HISTORY.rst

@@ -1,4 +1,4 @@
-0.6.0 (2020-03-18)
+0.6.0 (2020-??-??)
 ------------------
 
 * Update to the latest skosprovider version and implement the
@@ -9,6 +9,7 @@
   issue we wanted it to fix and it added a lot of overhead. A provider should 
   now be passed a :class:`sqlachemy.orm.session.Session` at startup, or a 
   callable that returns such a session. (#64)
+* Improved performance of getting the concept_scheme by caching it. (#71)
 * Drop support for Python 3.4. Add support for Python 3.7. This
   is also the last version to support Python 2. (#62)
 

skosprovider_sqlalchemy/providers.py

@@ -44,6 +44,12 @@ class SQLAlchemyProvider(VocabularyProvider):
     as backend.
     '''
 
+    _conceptscheme = None
+    '''
+    The concept scheme, once it has been loaded. Should never be accessed
+    directly.
+    '''
+
     expand_strategy = 'recurse'
     '''
     Determines how the expand method will operate. Options are:
@@ -96,7 +102,9 @@ def __init__(self, metadata, session, **kwargs):
 
     @property
     def concept_scheme(self):
-        return self._get_concept_scheme()
+        if self._conceptscheme is None:
+            self._conceptscheme = self._get_concept_scheme()
+        return self._conceptscheme
 
     def _get_concept_scheme(self):
         '''

tests/test_providers.py

@@ -116,6 +116,14 @@ def test_concept_scheme(self):
         assert 2 == len(cs.languages)
         assert 'en' in cs.languages
 
+    def test_concept_scheme_is_cached(self):
+        from skosprovider.skos import (
+            ConceptScheme
+        )
+        assert self.provider._conceptscheme is None
+        cs = self.provider.concept_scheme
+        assert self.provider._conceptscheme == cs
+
     def test_get_concept_by_id(self):
         from skosprovider.skos import Concept