如何检查Gsp中是否存在对象？

Question

<g:each in="${clientTripInstance?.startPointJob?.passengerActivities}" status="i" var="startPassengerActivity">
     <g:if test = "${startPassengerActivity?.passengerCount > 1}">
         <p> ${startPassengerActivity?.activity}  ${startPassengerActivity?.passengerRole?.displayName} (${startPassengerActivity?.passengerCount})
     </p>
     </g:if>
     <g:else>
       <p> ${startPassengerActivity?.activity}  ${startPassengerActivity?.passengerRole?.displayName}
          </p>
     </g:else>
</g:each>

当 clientTripInstance?.startPointJob?.passengerActivities 存在时，此代码工作正常。在某些情况下，clientTripInstance?.startPointJob?.passengerActivities 不存在...那么如何检查不存在？如果它不存在，我不想显示任何内容..

域类是

   class Trip {
            String notes
           List<PointJob> pointJobs = new ArrayList<PointJob>()
   }

   class PointJob {
       Point point
   List<PassengerActivity> passengerActivities = new ArrayList<PassengerActivity>();
   }


  class PassengerActivity {
    PassengerRole passengerRole;
    String activity;
    int passengerCount;

static constraints = {
    passengerRole()
    activity()
    passengerCount(nullable:true)
}

}

Answer 1

您不能将其全部包装在另一个测试中以确保列表不为空或为空吗？

<g:if test="${clientTripInstance?.startPointJob?.passengerActivities}">
  <g:each in="${clientTripInstance?.startPointJob?.passengerActivities}" status="i" var="startPassengerActivity">
    <g:if test = "${startPassengerActivity?.passengerCount > 1}">
      <p>
        ${startPassengerActivity?.activity}  ${startPassengerActivity?.passengerRole?.displayName} (${startPassengerActivity?.passengerCount})
      </p>
    </g:if>
    <g:else>
      <p>
        ${startPassengerActivity?.activity}  ${startPassengerActivity?.passengerRole?.displayName}
      </p>
    </g:else>
  </g:each>
</g:if>