add example

Author: norareidy

source/includes/interact-data/transactions.py

@@ -21,6 +21,24 @@ def insert_movie_transaction():
         )
 # 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"]
+        )
+
+        # Registers the callback to run only after the transaction commits
+        transaction.on_commit(get_horror_comedies)
+# end-callback
+
 # start-handle-errors
 movie = Movie.objects.get(
     title="Jurassic Park",

source/interact-data/transactions.txt

@@ -102,6 +102,24 @@ preceding example but uses a context manager to start a transaction:
    :language: python
    :copyable:
 
+Run Callbacks After a Transaction
+---------------------------------
+
+If you want to run certain operations only if a transaction successfully
+completes, you can us the ``on_commit()`` method. This method 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
 -------------------------