Update 'query_builder' option

The entity used in 'FROM' clause of 'query_builder' option will always be validated against the class which you have specified in form field option 'class'. If you return another entity instead of the one used in your FROM clause, for instance SELECT an entity from a joined table, it will break validation.

Author: Jonathan

reference/forms/types/entity.rst

@@ -203,6 +203,13 @@ passed the ``EntityRepository`` of the entity as the only argument and should
 return a ``QueryBuilder``. Returning ``null`` in the Closure will result in
 loading all entities.
 
+.. caution::
+
+    The entity used in ``FROM`` clause of `query_builder`_ option 
+    will always be validated against the class which you have specified in form field option `class`_. 
+    If you return another entity instead of the one used in your ``FROM`` clause, 
+    for instance ``SELECT`` an entity from a joined table, it will break validation.
+    
 Overridden Options
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