Fixes #226: atomic operations and transaction support in AR.

docs/api/db/ActiveRecord.md

@@ -446,3 +446,7 @@ $customers = Customer::find()->olderThan(50)->all();
 
 The parameters should follow after the `$query` parameter when defining the scope method, and they
 can take default values like shown above.
+
+### Atomic operations and scenarios
+
+TBD

docs/internals/ar.md

@@ -1,15 +1,50 @@
 ActiveRecord
 ============
 
+Scenarios
+---------
+
+All possible scenario formats supported by ActiveRecord:
+
+```php
+public function scenarios()
+{
+    return array(
+        // 1. attributes array
+        'scenario1' => array('attribute1', 'attribute2'),
+
+        // 2. insert, update and delete operations won't be wrapped with transaction (default mode)
+        'scenario2' => array(
+            'attributes' => array('attribute1', 'attribute2'),
+            'atomic' => array(), // default value
+        ),
+
+        // 3. all three operations (insert, update and delete) will be wrapped with transaction
+        'scenario3' => array(
+            'attributes' => array('attribute1', 'attribute2'),
+            'atomic',
+        ),
+
+        // 4. insert and update operations will be wrapped with transaction, delete won't
+        'scenario4' => array(
+            'attributes' => array('attribute1', 'attribute2'),
+            'atomic' => array(self::INSERT, self::UPDATE),
+        ),
+
+        // 5. insert and update operations won't be wrapped with transaction, delete will
+        'scenario5' => array(
+            'attributes' => array('attribute1', 'attribute2'),
+            'atomic' => array(self::DELETE),
+        ),
+    );
+}
+```
+
 Query
 -----
 
 ### Basic Queries
 
-
-
 ### Relational Queries
 
 ### Scopes
-
-