Extract common base functionality for storing xblock fields in the relation db

lms/djangoapps/courseware/models.py

@@ -130,38 +130,46 @@ class StudentModuleHistory(models.Model):
             history_entry.save()
 
 
-class XModuleUserStateSummaryField(models.Model):
+class XBlockFieldBase(models.Model):
     """
-    Stores data set in the Scope.user_state_summary scope by an xmodule field
+    Base class for all XBlock field storage.
     """
-
     class Meta:
-        unique_together = (('usage_id', 'field_name'),)
+        abstract = True
 
     # The name of the field
     field_name = models.CharField(max_length=64, db_index=True)
 
-    # The definition id for the module
-    usage_id = LocationKeyField(max_length=255, db_index=True)
-
     # The value of the field. Defaults to None dumped as json
     value = models.TextField(default='null')
 
     created = models.DateTimeField(auto_now_add=True, db_index=True)
     modified = models.DateTimeField(auto_now=True, db_index=True)
 
-    def __repr__(self):
-        return 'XModuleUserStateSummaryField<%r>' % ({
-            'field_name': self.field_name,
-            'usage_id': self.usage_id,
-            'value': self.value,
-        },)
-
     def __unicode__(self):
-        return unicode(repr(self))
+        return u'{}<{!r}'.format(
+            self.__class__.__name__,
+            {
+                key:getattr(self, key)
+                for key in self._meta.get_all_field_names()
+                if key not in ('created', 'modified')
+            }
+        )
+
+
+class XModuleUserStateSummaryField(XBlockFieldBase):
+    """
+    Stores data set in the Scope.user_state_summary scope by an xmodule field
+    """
+
+    class Meta:
+        unique_together = (('usage_id', 'field_name'),)
+
+    # The definition id for the module
+    usage_id = LocationKeyField(max_length=255, db_index=True)
 
 
-class XModuleStudentPrefsField(models.Model):
+class XModuleStudentPrefsField(XBlockFieldBase):
     """
     Stores data set in the Scope.preferences scope by an xmodule field
     """
@@ -169,33 +177,13 @@ class XModuleStudentPrefsField(models.Model):
     class Meta:
         unique_together = (('student', 'module_type', 'field_name'),)
 
-    # The name of the field
-    field_name = models.CharField(max_length=64, db_index=True)
-
     # The type of the module for these preferences
     module_type = models.CharField(max_length=64, db_index=True)
 
-    # The value of the field. Defaults to None dumped as json
-    value = models.TextField(default='null')
-
     student = models.ForeignKey(User, db_index=True)
 
-    created = models.DateTimeField(auto_now_add=True, db_index=True)
-    modified = models.DateTimeField(auto_now=True, db_index=True)
-
-    def __repr__(self):
-        return 'XModuleStudentPrefsField<%r>' % ({
-            'field_name': self.field_name,
-            'module_type': self.module_type,
-            'student': self.student.username,
-            'value': self.value,
-        },)
 
-    def __unicode__(self):
-        return unicode(repr(self))
-
-
-class XModuleStudentInfoField(models.Model):
+class XModuleStudentInfoField(XBlockFieldBase):
     """
     Stores data set in the Scope.preferences scope by an xmodule field
     """
@@ -203,27 +191,8 @@ class XModuleStudentInfoField(models.Model):
     class Meta:
         unique_together = (('student', 'field_name'),)
 
-    # The name of the field
-    field_name = models.CharField(max_length=64, db_index=True)
-
-    # The value of the field. Defaults to None dumped as json
-    value = models.TextField(default='null')
-
     student = models.ForeignKey(User, db_index=True)
 
-    created = models.DateTimeField(auto_now_add=True, db_index=True)
-    modified = models.DateTimeField(auto_now=True, db_index=True)
-
-    def __repr__(self):
-        return 'XModuleStudentInfoField<%r>' % ({
-            'field_name': self.field_name,
-            'student': self.student.username,
-            'value': self.value,
-        },)
-
-    def __unicode__(self):
-        return unicode(repr(self))
-
 
 class OfflineComputedGrade(models.Model):
     """