[TYPO3-dev] Checkbox-viewhelper doesn't handle ObjectStorages correctly regarding object-creation

[Michael Bakonyi]

Hi everone,

Use case: Via a fluid form you want to create an object with an 
associated property of type ObjectStorage (e.g. an 1:n-relation). The 
records of the property shall be represented via checkboxes.

The problem is, that the checkbox-viewhelper only rendeders the 
name-attribute correclty like this 
"tx_myExt_pi1[myObject][myProperty][]" (with the extended 
"[]"-characters at the end) when there's a form-object already. So if 
you want to edit your object, everything's fine, as the object is 
already existant/persisted. In case you don't have a form-object as you 
want to create a new object with the form the viewhelper doesn't 
generate an array-value within the name-attribute. This results in not 
persisted form-values.

The code-problem in detail:

The checkbox-viewhelper tries to get the property-value via 
getPropertyValue() which comes from AbstractFormFieldViewHelper.php. 
Based on the returned value of this function the decision is taken to 
extend the regular value of the name-attribute with the needed 
"[]"-characters or not. In the function getPropertyValue() there's a 
check for the existance for a form-object (see also 
https://forge.typo3.org/issues/35894) and if no such object is existing 
the function returns nothing and thus no "[]"-characters are added.

I could provide a patch with which a new attribute "multiple" is 
registered for the checkbox-viewhelper. So even if the propertyValue 
returns nothing the characters get added, if multiple="1" is set for the 
checkbox-viewhelper.

But I don't think this is a clean approach and would like to hear some 
thoughts of you, who are more familiar with all the fluid-generation 
including sideffects regarding changes within the core-code.

Cheers,
Michael