Symfony datetime field format
Have you tried the following date_format in your datetime definition?
'yyyy-MM-dd HH:mm'instead of what you have now:
'yyyy-MM-dd HH:i'I think you're mixing PHP date format options with the RFC format options the symfony form builder expects, according to the documentation. Peruse the accepted RFC datetime formats to see how to tweak it.
You should use the format option which accepts HTML5 DateTime format.
$builder->add( 'beginDate', 'datetime', array( 'widget' => 'single_text', 'format' => 'yyyy-MM-dd HH:mm' ))The format option should be used instead of date_format when using widget = single_text.