Dynamic lightning:inputfield validation not working

Question

I am trying to set a validation on a dynamic lightning:inputfield bus this is not working neighter do I get an error. I think my binding isn't correct.

Component

<aura:iteration items="{!v.fields}" var="field" >
                <aura:if isTrue="{!v.inputModeBool == true? true: false}">
                    <lightning:inputField fieldName="{!field.fieldPath}"  aura:id="{!field.fieldPath}"/>{!field.required}
                </aura:if>
                <aura:if isTrue="{!v.inputModeBool != true? true: false}">
                    <lightning:layout >
                        <lightning:layoutitem size="10">
                            <lightning:outputField fieldName="{!field.fieldPath}"/>
                        </lightning:layoutitem>
                        <lightning:layoutitem size="2">
                            <lightning:buttonIcon iconName="utility:edit" variant="bare"
                                                  alternativeText="edit"
                                                  onclick="{!c.next}"/>
                        </lightning:layoutitem>
                    </lightning:layout>
                </aura:if>
            </aura:iteration>

Controller

   next: function(component, event, helper) {
         alert('Whoohooo');
       var invalidFields = helper.isFormValid(component);
    if(invalidFields && invalidFields.length > 0){
        helper.reportUserError(
            'Please complete all required fields',
            'Incomplete: '+ invalidFields.join(', ')
        );
        event.preventDefault();
        return;
    }
    },

Helper

    isFormValid: function (component) {
    return (component.find('field.fieldPath') || [])
        .filter(function (i) {
            var value = i.get('v.value');
            return !value || value == '' || value.trim().length === 0;
        })
        .map(function (i) {
            return i.get('v.fieldName');
        });
}

Answer 1

1. lightning:inputField cannot be used without recordEditForm.
2. aura:id cannot be dynamic. It should be static. That is, you cannot mention it as {!dynamicValue}. You rather give it static value like "myInputField"
3. You cannot check validity in inputField, you can check custom validity on lightning:input. Documentation says:

Usage Considerations To persist requiredness on a field, select the Required checkbox when defining the custom field in Setup. A required field is displayed with a red asterisk next to the field label. An error message is displayed below a required field if you try to submit the form before entering a value.

By making aura:id as static, you can find it. If there is single element with that aura:id, it will return single element. If there there are multiple elements with same name, (like in iteration) then it will return array of elements. Ref: https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/components_ids.htm