DB writer: avoid instantiating multiple instances of the same propert…

…y class

tangos/properties/__init__.py

@@ -555,9 +555,15 @@ def providing_classes(property_name_list, handler_class, silent_fail=False, expl
 def instantiate_classes(simulation, property_name_list, silent_fail=False, explain=False):
     """Instantiate appropriate property calculation classes for a given simulation and list of property names."""
     instances = []
+    already_instantiated_classes = []
+
     handler_class = type(simulation.get_output_handler())
+
     for property_identifier in property_name_list:
-        instances.append(providing_class(property_identifier, handler_class, silent_fail, explain)(simulation))
+        cl = providing_class(property_identifier, handler_class, silent_fail, explain)
+        if cl not in already_instantiated_classes:
+            already_instantiated_classes.append(cl)
+            instances.append(cl(simulation))
 
     return instances
 

tests/test_db_writer.py

@@ -342,3 +342,21 @@ def test_writer_reports_aggregates(fresh_database):
 
     assert "Succeeded: 15 property calculations" in res
     assert "myPropertyTakingTime         1.5s" in res
+
+
+class MoreThanOneDummyProperty(properties.PropertyCalculation):
+    names = "dummy_property_t1", "dummy_property_t2"
+    requires_particle_data = True
+
+    def requires_property(self):
+        return []
+
+    def calculate(self, data, entry):
+        return data.time*data.halo, data.time*data.halo+1
+
+def test_writer_doesnt_duplicate_property_classes(fresh_database):
+    res = run_writer_with_args("dummy_property_t1", "dummy_property_t2")
+    assert "Succeeded: 15" in res
+    assert "Already exists: 0" in res
+    assert db.get_halo("dummy_sim_1/step.1/1")['dummy_property_t1'] == 1.0
+    assert db.get_halo("dummy_sim_1/step.1/1")['dummy_property_t2'] == 2.0