Successfully read course children out of mongodb

cms/lib/keystore/__init__.py

@@ -60,6 +60,40 @@ class KeyStore(object):
         with the specified location.
 
         If no object is found at that location, raises keystore.exceptions.ItemNotFoundError
+
+        Searches for all matches of a partially specifed location, but raises an
+        keystore.exceptions.InsufficientSpecificationError if more
+        than a single object matches the query.
+
+        location: Something that can be passed to Location
+        """
+        raise NotImplementedError
+
+    def create_item(self, location, editor):
+        """
+        Create an empty item at the specified location with the supplied editor
+
+        location: Something that can be passed to Location
+        """
+        raise NotImplementedError
+
+    def update_item(self, location, data):
+        """
+        Set the data in the item specified by the location to
+        data
+
+        location: Something that can be passed to Location
+        data: A nested dictionary of problem data
+        """
+        raise NotImplementedError
+
+    def update_children(self, location, children):
+        """
+        Set the children for the item specified by the location to
+        data
+
+        location: Something that can be passed to Location
+        children: A list of child item identifiers
         """
         raise NotImplementedError
 

cms/lib/keystore/exceptions.py

@@ -5,3 +5,7 @@ Exceptions thrown by KeyStore objects
 
 class ItemNotFoundError(Exception):
     pass
+
+
+class InsufficientSpecificationError(Exception):
+    pass

cms/lib/keystore/mongo.py

@@ -1,6 +1,6 @@
 import pymongo
-from . import KeyStore
-from .exceptions import ItemNotFoundError
+from . import KeyStore, Location
+from .exceptions import ItemNotFoundError, InsufficientSpecificationError
 
 
 class MongoKeyStore(KeyStore):
@@ -12,15 +12,64 @@ class MongoKeyStore(KeyStore):
             host=host,
             port=port
         )[db][collection]
+        
+        # Force mongo to report errors, at the expense of performance
+        self.collection.safe = True
 
     def get_children_for_item(self, location):
-        item = self.collection.find_one(
-            {'location': location.dict()},
+        query = dict(
+            ('location.{key}'.format(key=key), val)
+            for (key, val)
+            in Location(location).dict().items()
+            if val is not None
+        )
+        items = self.collection.find(
+            query,
             fields={'children': True},
             sort=[('revision', pymongo.ASCENDING)],
+            limit=1,
+        )
+        if items.count() > 1:
+            raise InsufficientSpecificationError(location)
+
+        if items.count() == 0:
+            raise ItemNotFoundError(location)
+
+        return items[0]['children']
+
+    def create_item(self, location, editor):
+        """
+        Create an empty item at the specified location with the supplied editor
+
+        location: Something that can be passed to Location
+        """
+        self.collection.insert({
+            'location': Location(location).dict(),
+            'editor': editor
+        })
+
+    def update_item(self, location, data):
+        """
+        Set the data in the item specified by the location to
+        data
+
+        location: Something that can be passed to Location
+        data: A nested dictionary of problem data
+        """
+        self.collection.update(
+            {'location': Location(location).dict()},
+            {'$set': {'data': data}}
         )
 
-        if item is None:
-            raise ItemNotFoundError()
+    def update_children(self, location, children):
+        """
+        Set the children for the item specified by the location to
+        data
 
-        return item['children']
+        location: Something that can be passed to Location
+        children: A list of child item identifiers
+        """
+        self.collection.update(
+            {'location': Location(location).dict()},
+            {'$set': {'children': children}}
+        )