The validation plugin only amends the value
and checked
binding to make them automatically "validation" compatible.
So the selectedOptions
is not automatically validated so you need to call makeBindingHandlerValidatable
with the selectedOptions
before the ko.applyBindings
to make the validation work with your multi select:
ko.validation.makeBindingHandlerValidatable('selectedOptions');
ko.applyBindings(new viewModel);
Demo JSFiddle.
As an alternative solution you can also you the validationCore
(or the validationMessage
binding on separate span) on your select:
<select data-bind="selectedOptions: seekingTypes,
options: memberTypeSource,
optionsText: 'text',
optionsValue: 'id', validationCore: seekingTypes"
multiple></select>
Demo JSFiddle.