How to multiple checbox using same ng-model?

I am using ionic framework for mobile app development.Set multiple checkbox using same ng-model,when i click one checkbox all three checkboxes should be clicked.And the values does not store.But i want normal HTML checkboxes (i.e)values stored same field in db with coma(,) seperated.

<label class="item item-input item-floating-label">Gender</label>
   <input type="radio" ng-model="data.days" value="sunday">sunday
  <input type="radio" ng-model="data.days" value="monday">monday