docs: add docs for temporary records functionality

Author: daireto

README.md

@@ -257,7 +257,19 @@ await user.delete()
 > (i.e. a boolean `is_deleted` column).
 
 > [!TIP]
-> Check the [Active Record Mixin API Reference](https://daireto.github.io/sqlactive/api/active-record-mixin/#api-reference)
+> If you need to create a record for a short period of time, you can use the
+> `with` statement:
+> ```python
+> with User(name='Bob', age=30) as user:
+>     ...
+> ```
+> The `with` statement will create the record and delete it at the end of the
+> block.
+>
+> Check the [Temporary Records documentation](https://daireto.github.io/sqlactive/api/active-record-mixin/#temporary-records)
+> for more information.
+>
+> Also, check the [Active Record Mixin API Reference](https://daireto.github.io/sqlactive/api/active-record-mixin/#api-reference)
 > to see all the available methods.
 
 ### 4. Perform Bulk Operations

docs/api/active-record-mixin.md

@@ -195,6 +195,48 @@ await User.delete_all(users)
 await User.destroy(1, 2, 3)  # Deletes users with IDs 1, 2, and 3
 ```
 
+#### Temporary Records
+
+If you need to create a record for a short period of time, you can use the
+`with` statement:
+
+```python
+with User(name='Bob', age=30) as user:
+    ...
+```
+
+The `with` statement will create the record using the [`save()`](#save) method.
+The record will be deleted at the end of the block using the [`delete()`](#delete).
+
+Here is an example of using temporary records to test the [`isnull`](smart-query-mixin.md#isnull) filter operator:
+
+```python
+post1 = Post(
+    title='Lorem ipsum',
+    body='Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
+    rating=4,
+    user_id=1,
+    topic='Some topic',  # this post has a topic
+)
+post2 = Post(
+    title='Lorem ipsum',
+    body='Lorem ipsum dolor sit amet, consectetur adipiscing elit.',
+    rating=4,
+    user_id=1,  # this post does not have a topic
+)
+
+# post1 and post2 will be deleted at the end of the block
+async with post1, post2:
+
+    # If isnull=True, only posts without a topic must be returned
+    posts = await Post.where(topic__isnull=True).all()
+    assert all([p.topic is None for p in posts]) is True
+
+    # If isnull=False, only posts with a topic must be returned
+    posts = await Post.where(topic__isnull=False).all()
+    assert all([post.topic is not None for p in posts]) is True
+```
+
 ### Querying
 
 #### Basic Queries

docs/getting-started.md

@@ -191,7 +191,21 @@ await user.delete()
 
 ???+ tip
 
-    Check the [Active Record Mixin API Reference](api/active-record-mixin.md#api-reference)
+    If you need to create a record for a short period of time, you can use the
+    `with` statement:
+
+    ```python
+    with User(name='Bob', age=30) as user:
+        ...
+    ```
+
+    The `with` statement will create the record and delete it at the end of the
+    block.
+
+    Check the [Temporary Records documentation](api/active-record-mixin.md#temporary-records)
+    for more information.
+
+    Also, check the [Active Record Mixin API Reference](api/active-record-mixin.md#api-reference)
     to see all the available methods.
 
 ### 4. Perform Bulk Operations