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[Form] Inserted a warning about a limitation of model transformers #15780

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Oct 8, 2021
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[Form] Inserted a warning about a limitation of model transformers #15780

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15 changes: 15 additions & 0 deletions form/data_transformers.rst
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Expand Up @@ -482,6 +482,21 @@ Which transformer you need depends on your situation.

To use the view transformer, call ``addViewTransformer()``.

.. caution::

Be careful with model transformers and
:doc:`Collection </reference/forms/types/collection>` field types: As the
Collection's children are created early at `PRE_SET_DATA` by its
`ResizeFormListener`, their data is populated later from the Norm Data. So
your model transformer cannot reduce the number of items within the
Collection (i.e. filtering out some items), as in that case the collection
ends up with some empty children.

A possible workaround for that limitation could be not using the underlying
object directly, but a DTO (Data Transfer Object) instead, that implements
the transformation of such incompatible data structures.


So why Use the Model Transformer?
---------------------------------

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