Save randomization seed if it is not already set,

so that the same problem loads when the user
checks/saves/resets

common/lib/xmodule/xmodule/capa_module.py

@@ -150,6 +150,16 @@ class CapaModule(CapaFields, XModule):
             # TODO (vshnayder): move as much as possible of this work and error
             # checking to descriptor load time
             self.lcp = self.new_lcp(self.get_state_for_lcp())
+
+            # At this point, we need to persist the randomization seed
+            # so that when the problem is re-loaded (to check/view/save)
+            # it stays the same.
+            # However, we do not want to write to the database
+            # every time the module is loaded.
+            # So we set the seed ONLY when there is not one set already
+            if self.seed is None:
+                self.seed = self.lcp.seed
+
         except Exception as err:
             msg = 'cannot create LoncapaProblem {loc}: {err}'.format(
                 loc=self.location.url(), err=err)

common/lib/xmodule/xmodule/tests/test_capa_module.py

@@ -868,10 +868,8 @@ class CapaModuleTest(unittest.TestCase):
             module = CapaFactory.create(rerandomize=rerandomize)
 
             # Get the seed
-            # This isn't stored in the XModule until
-            # we check/save/reset the problem, so we
-            # access the lcp seed directly
-            seed = module.lcp.seed
+            # By this point, the module should have persisted the seed
+            seed = module.seed
             self.assertTrue(seed is not None)
 
             # If we're not rerandomizing, the seed is always set
@@ -931,10 +929,9 @@ class CapaModuleTest(unittest.TestCase):
             module = CapaFactory.create(rerandomize=rerandomize)
 
             # Get the seed
-            # This isn't stored in the XModule until
-            # we check/save/reset the problem, so we
-            # access the lcp seed directly
-            seed = module.lcp.seed
+            # By this point, the module should have persisted the seed
+            seed = module.seed
+            self.assertTrue(seed is not None)
 
             # We do NOT want the seed to reset if rerandomize
             # is set to 'never' -- it should still be 1