[TYPO3-mvc] groupedFor and date object

[Manfred Rutschmann]

Hey guys,

i have a date property in my model and i would use this date for build
groups in frontend, but it doenst work:


<f:groupedFor each="{cards}" as="cardgroup" groupBy="date" groupKey="key">

#1273753083: Cannot cast object of type "DateTime" to string. 

Tx_Fluid_Core_Parser_Exception thrown in file
/home/revier.cc/domains/wochenblatt-online-de.revier.cc/public_html/typo3/sysext/fluid/Classes/Core/Parser/SyntaxTree/AbstractNode.php
in line 57.


Another test:

<f:groupedFor each="{cards}" as="cardgroup" groupBy="date.getTimestamp"
groupKey="key">

#1263391473: The property "date.getTimestamp" on the subject was not
accessible. 

Tx_Extbase_Reflection_Exception_PropertyNotAccessibleException thrown in
file
/home/revier.cc/domains/wochenblatt-online-de.revier.cc/public_html/typo3/sysext/extbase/Classes/Reflection/ObjectAccess.php
in line 79.


How can i handle this?

Thx and regards Manfred