<aura:component implements="force:appHostable">
<aura:attribute name="recordId" type="String" />
<lightning:card title="Create Reservation">
    <lightning:recordEditForm
                              onsuccess="{!c.handleSuccess}"
                              objectApiName="Campsite_Reservation__c">
        <!-- the messages component is for error messages -->
        <lightning:messages />
        <lightning:inputField fieldName="Campsite__c" value="a041o00000ZWoFbAAL"/>
        <lightning:inputField fieldName="Reference__c"/>
        <div class="slds-m-top_medium">
            <lightning:button variant="brand" type="submit" name="save" label="Save" />
        </div>
    </lightning:recordEditForm>
</lightning:card>

({

handleSuccess: function(cmp, event, helper) {
    var params = event.getParams();
    cmp.set('v.recordId', params.response.id);
}