DOCSP-51036: Transactions

source/includes/interact-data/transactions.py

@@ -0,0 +1,54 @@
+from django.db import transaction, DatabaseError
+from sample_mflix.models import Movie
+
+# start-transaction-decorator
+@transaction.atomic
+def insert_movie_transaction():
+    Movie.objects.create(
+        title="Poor Things",
+        runtime=141,
+        genres=["Comedy", "Romance"]
+    )
+# end-transaction-decorator
+
+# start-transaction-manager
+def insert_movie_transaction():
+    with transaction.atomic():
+        Movie.objects.create(
+            title="Poor Things",
+            runtime=141,
+            genres=["Comedy", "Romance"]
+        )
+# end-transaction-manager
+
+# start-callback
+def get_horror_comedies():
+    movies = Movie.objects.filter(genres=["Horror", "Comedy"])
+    for m in movies:
+        print(f"Title: {m.title}, runtime: {m.runtime}")
+
+def insert_movie_with_callback():
+    with transaction.atomic():
+        Movie.objects.create(
+            title="The Substance",
+            runtime=140,
+            genres=["Horror", "Comedy"]
+        )
+        transaction.on_commit(get_horror_comedies)
+# end-callback
+
+# start-handle-errors
+movie = Movie.objects.get(title="Jurassic Park")
+movie.title = "Jurassic Park I"
+try:
+    with transaction.atomic():
+        movie.save()
+except DatabaseError:
+    movie.title = "Jurassic Park"
+
+if movie.title == "Jurassic Park I":
+    movie.plot = "An industrialist invites experts to visit his theme park of cloned dinosaurs. After a power failure," \
+    "   the creatures run loose, putting everyone's lives, including his grandchildren's, in danger."
+    movie.save()
+
+# end-handle-errors

source/interact-data.txt

@@ -24,6 +24,7 @@ Interact with Data
    CRUD Operations </interact-data/crud>
    Specify a Query </interact-data/specify-a-query>
    Perform Raw Queries </interact-data/raw-queries>
+   Transactions </interact-data/transactions>
 
 In this section, you can learn how to use {+django-odm+} to interact with your
 MongoDB data.
@@ -36,3 +37,6 @@ MongoDB data.
 
 - :ref:`django-raw-queries`: Learn how to use MongoDB's aggregation pipeline syntax
   or the PyMongo driver to query your data.
+
+- :ref:`django-transactions`: Learn how to use {+framework+}'s transaction API
+  to run data operations within a transaction.

source/interact-data/raw-queries.txt

@@ -164,19 +164,10 @@ that covers the fields you want to query. Then, pass a ``$search``
 or ``$searchMeta`` stage in an aggregation pipeline parameter to
 the ``raw_aggregate()`` method.
 
-.. important:: 
+.. tip:: 
 
-   You cannot use the ``QuerySet`` API to create Atlas Search indexes.
-   However, you can create an index by exposing your ``MongoClient``
-   object directly, on which you can call the PyMongo driver's 
-   ``create_search_index()`` method. To learn how to expose the
-   ``MongoClient``, see the :ref:`django-client-operations` section
-   of this guide.
-
-   For instructions on using the PyMongo driver to create an Atlas
-   Search index, see `Atlas Search and Vector Search Indexes
-   <{+pymongo-docs+}/indexes/atlas-search-index/>`__
-   in the PyMongo documentation.
+   To learn how to create Atlas Search indexes, see :ref:`django-indexes-atlas-search`
+   in the Create Indexes guide.
 
 This example runs an Atlas Search query by passing the ``$search`` pipeline
 stage to the ``raw_aggregate()`` method. The code performs the following

source/interact-data/transactions.txt

@@ -0,0 +1,156 @@
+.. _django-transactions:
+
+=========================
+Transactions and Sessions
+=========================
+
+.. facet::
+   :name: genre
+   :values: reference
+
+.. meta::
+   :keywords: code example, ACID compliance, multi-document
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+Overview
+--------
+
+In this guide, you can learn how to use {+django-odm+} to perform
+**transactions**. Transactions allow you to run a series of operations
+that change data only if the entire transaction is committed.
+If any operation in the transaction does not succeed, {+django-odm+} stops the
+transaction and discards all changes to the data before they ever become
+visible. This feature is called **atomicity**.
+
+In MongoDB, transactions run within logical sessions. A
+session is a grouping of related read or write operations that you
+want to run sequentially. Sessions enable causal consistency for a group
+of operations and allow you to run operations in an **ACID-compliant**
+transaction, which is a transaction that meets an expectation of
+atomicity, consistency, isolation, and durability. 
+
+You can use {+framework+}'s transaction API to perform database transactions.
+To run operations within a transaction, define them inside an atomic block of
+code. {+framework+} manages session logic internally, so you do not need to
+manually start a session before running a transaction.
+
+.. important:: Transaction Limitations
+
+   {+django-odm+}'s support for the {+framework+} transaction API
+   has several limitations. To view a list of limitations, see
+   :ref:`Database and Collection Support <django-feature-compat-db-coll>`
+   in the {+framework+} and MongoDB Feature Compatibility guide.
+
+Sample Data
+~~~~~~~~~~~
+
+The examples in this guide use the ``Movie`` model, which represents
+the ``sample_mflix.movies`` collection from the :atlas:`Atlas sample datasets </sample-data>`.
+The ``Movie`` model class has the following definition:
+
+.. literalinclude:: /includes/interact-data/crud.py
+   :start-after: start-models
+   :end-before: end-models
+   :language: python
+   :copyable:
+
+.. include:: /includes/use-sample-data.rst
+
+   .. replacement:: model-classes
+
+      ``Movie`` model includes
+
+   .. replacement:: model-imports
+
+      .. code-block:: python
+
+         from <your application name>.models import Movie
+         from django.utils import timezone
+         from datetime import datetime
+
+Start a Transaction
+-------------------
+
+To start a database transaction, define an atomic block of code
+by adding the ``@transaction.atomic`` decorator above your function.
+This decorator guarantees the atomicity of any database operations
+within the function. If the function successfully completes, the 
+changes are committed to MongoDB.
+
+The following example calls the ``create()`` method within a transaction,
+which inserts a document into the ``sample_mflix.movies`` collection if the
+transaction succeeds:
+
+.. literalinclude:: /includes/interact-data/transactions.py
+   :start-after: start-transaction-decorator
+   :end-before: end-transaction-decorator
+   :language: python
+   :copyable:
+
+Alternatively, you can use the ``transaction.atomic()`` context manager
+to create an atomic block. This example runs the same operation as the
+preceding example but uses a context manager to start a transaction:
+
+.. literalinclude:: /includes/interact-data/transactions.py
+   :start-after: start-transaction-manager
+   :end-before: end-transaction-manager
+   :language: python
+   :copyable:
+
+Run Callbacks After a Transaction
+---------------------------------
+
+To perform certain actions only if a transaction successfully completes,
+you can use the ``transaction.on_commit()`` function. This function allows you to
+register callbacks that run after a transaction is committed to the 
+database. Pass a function, or any callable object, as an argument to
+``on_commit()``.
+
+The following example queries for movies that have a ``genre`` value of
+``["Horror", "Comedy"]`` only after a related database transaction completes:
+
+.. literalinclude:: /includes/interact-data/transactions.py
+   :start-after: start-callback
+   :end-before: end-callback
+   :language: python
+   :copyable:
+
+Handle Transaction Errors
+-------------------------
+
+To handle exceptions that occur during a transaction, add error handling
+logic around your atomic code block. If you handle errors inside
+the atomic block, you might obscure these errors from {+framework+}. Since
+{+framework+} uses errors to determine whether to commit or roll
+back a transaction, this can cause unexpected behavior.
+
+If a transaction does not succeed, {+framework+} does not revert any changes made
+to a model's fields. To avoid inconsistencies between your models and database documents,
+you might need to manually restore the original field values.
+
+Example
+~~~~~~~
+
+The following example includes error handling logic that reverts the modified
+``title`` value of the retrieved document if the database transaction fails:
+
+.. literalinclude:: /includes/interact-data/transactions.py
+   :start-after: start-handle-errors
+   :end-before: end-handle-errors
+   :language: python
+   :copyable:
+
+Since the code performs a second database operation based on the
+model's ``title`` value, reverting the change if the transaction errors
+prevents further data inconsistencies.
+
+Additional Information
+----------------------
+
+To learn more about the {+framework+} transaction API, see `Database Transactions
+<{+django-docs+}/topics/db/transactions>`__ in the {+framework+} documentation.

source/limitations-upcoming.txt

@@ -183,6 +183,8 @@ Query Support
        the :ref:`raw_aggregate() method <django-raw-queries-search>`.
      - ✓
 
+.. _django-feature-compat-db-coll:
+
 Database and Collection Support
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -248,7 +250,15 @@ Database and Collection Support
      - ✓
 
    * - Transactions
-     - *Unsupported*.
+     - ✓ You can use {+framework+}'s transactions API with the
+       following limitations:
+
+       - ``QuerySet.union()`` is not supported within a transaction.
+       - If a transaction generates an error, the transaction is no longer usable.
+       - Savepoints, or nested atomic blocks, are not supported. The outermost atomic block starts
+         a transaction, and any subsequent atomic blocks have no effect.
+       - Migration operations do not run inside a transaction.
+       - Your MongoDB deployment must be a replica set or sharded cluster.
      - ✓
 
 Django Features