Merge pull request apache#513 from datastax/py323-docs

aboudreault · aboudreault · commit f284fb1c16c0 · 2016-03-04T17:02:27.000-05:00
Py323 docs
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
@@ -46,6 +46,24 @@ Bug Fixes
 * cqlengine: class.MultipleObjectsReturned has DoesNotExist as base class (PYTHON-489)
 * cqlengine: Typo in cqlengine UserType __len__ breaks attribute assignment (PYTHON-502)
 
+
+Other
+-----
+
+* cqlengine: a major improvement on queryset has been introduced. It
+  is a lot more efficient to iterate large datasets: the rows are
+  now fetched on demand using the driver pagination.
+
+* cqlengine: the queryset len() and count() behaviors have changed. It
+  now executes a "SELECT COUNT(*)" of the query rather than returning
+  the size of the internal result_cache (loaded rows). On large
+  queryset, you might want to avoid using them due to the performance
+  cost. Note that trying to access objects using list index/slicing
+  with negative indices also requires a count to be
+  executed.
+
+
+
 3.0.0
 =====
 November 24, 2015
diff --git a/cassandra/cqlengine/query.py b/cassandra/cqlengine/query.py
@@ -700,7 +700,9 @@ class Comment(Model):
 
     def count(self):
         """
-        Returns the number of rows matched by this query
+        Returns the number of rows matched by this query.
+
+        *Note: This function executes a SELECT COUNT() and has a performance cost on large datasets*
         """
         if self._batch:
             raise CQLEngineException("Only inserts, updates, and deletes are available in batch mode")
@@ -751,14 +753,19 @@ class Automobile(Model):
 
     def limit(self, v):
         """
-        Limits the number of results returned by Cassandra.
+        Limits the number of results returned by Cassandra. Use *0* or *None* to disable.
 
         *Note that CQL's default limit is 10,000, so all queries without a limit set explicitly will have an implicit limit of 10,000*
 
         .. code-block:: python
 
+            # Fetch 100 users
             for user in User.objects().limit(100):
                 print(user)
+
+            # Fetch all users
+            for user in User.objects().limit(None):
+                print(user)
         """
 
         if v is None:
@@ -780,7 +787,7 @@ def fetch_size(self, v):
         """
         Sets the number of rows that are fetched at a time.
 
-        *Note that driver's default fetch size is 5000.
+        *Note that driver's default fetch size is 5000.*
 
         .. code-block:: python
 
diff --git a/docs/api/cassandra/cqlengine/query.rst b/docs/api/cassandra/cqlengine/query.rst
@@ -18,6 +18,12 @@ The methods here are used to filter, order, and constrain results.
 
     .. automethod:: count
 
+    .. method:: len(queryset)
+
+       Returns the number of rows matched by this query. This function uses :meth:`~.cassandra.cqlengine.query.ModelQuerySet.count` internally.
+
+       *Note: This function executes a SELECT COUNT() and has a performance cost on large datasets*
+
     .. automethod:: distinct
 
     .. automethod:: filter
@@ -26,6 +32,8 @@ The methods here are used to filter, order, and constrain results.
 
     .. automethod:: limit
 
+    .. automethod:: fetch_size
+
     .. automethod:: if_not_exists
 
     .. automethod:: if_exists
diff --git a/docs/cqlengine/queryset.rst b/docs/cqlengine/queryset.rst
@@ -79,6 +79,10 @@ Accessing objects in a QuerySet
             q[0] #returns the first result
             q[1] #returns the second result
 
+        .. note::
+
+            * CQL does not support specifying a start position in it's queries. Therefore, accessing elements using array indexing will load every result up to the index value requested
+            * Using negative indices requires a "SELECT COUNT()" to be executed. This has a performance cost on large datasets.
 
     * list slicing
         .. code-block:: python
@@ -87,7 +91,10 @@ Accessing objects in a QuerySet
             q[1:] #returns all results except the first
             q[1:9] #returns a slice of the results
 
-        *Note: CQL does not support specifying a start position in it's queries. Therefore, accessing elements using array indexing / slicing will load every result up to the index value requested*
+        .. note::
+
+            * CQL does not support specifying a start position in it's queries. Therefore, accessing elements using array slicing will load every result up to the index value requested
+            * Using negative indices requires a "SELECT COUNT()" to be executed. This has a performance cost on large datasets.
 
     * calling :attr:`get() <query.QuerySet.get>` on the queryset
         .. code-block:: python
