Question

我正在尝试通过文档快照来使用分页来定义查询游标。

第一次打开片段时，在onCreateView中，我使用下面的代码从firestore获取7个事件

fun getAllSearchedEventsFromTheBeginning(startDate: Date, endDate: Date, selectedCity: String, selectedEventType: String, limit: Long, completion: (errorMessage:String?, events: ArrayList<Event>?, lastDocument: DocumentSnapshot?) -> Unit) {

        // not only free events, paid events are also included

        FirestoreCollectionReference.event.getReference()
            .whereEqualTo(FIRESTORE_EVENT_FIELD_CITY,selectedCity)
            .whereEqualTo(FIRESTORE_EVENT_FIELD_EVENT_TYPE, selectedEventType)
            .whereEqualTo(FIRESTORE_EVENT_FIELD_HAS_BEEN_APPROVED,true)
            .whereGreaterThan(FIRESTORE_EVENT_FIELD_DATE_START_TIME,startDate)
            .whereLessThan(FIRESTORE_EVENT_FIELD_DATE_START_TIME,endDate)
            .orderBy(FIRESTORE_EVENT_FIELD_DATE_START_TIME, Query.Direction.ASCENDING)
            .limit(limit)
            .get()
            .addOnSuccessListener { snapshot ->

                val lastDocument = snapshot.documents[snapshot.size() - 1]

                val eventDocuments = snapshot.documents

                val eventArray = ArrayList<Event>()

                for (document in eventDocuments) {
                    val eventData = document.data
                    val event = Event(dataEvent = eventData)
                    eventArray.add(event)
                }

                completion(null,eventArray, lastDocument)

            }.addOnFailureListener {
                completion(it.localizedMessage,null,null)
            }

    }

我正在使用lamda表达式发送lastVisible文档，该lastVisible文档将用作下一个查询的起点

到达回收站视图的底部之后，我使用下面的代码从firestore中获取接下来的7个文档

fun getAllSearchedEventsAfterLastDocument(startDate: Date, endDate: Date, selectedCity: String, selectedEventType: String, limit: Long, lastDocument: DocumentSnapshot?, completion: (errorMessage:String?, events: ArrayList<Event>?, lastDocument: DocumentSnapshot?) -> Unit) {

        // not only free events, paid events are also included

        FirestoreCollectionReference.event.getReference()
            .whereEqualTo(FIRESTORE_EVENT_FIELD_CITY,selectedCity)
            .whereEqualTo(FIRESTORE_EVENT_FIELD_EVENT_TYPE, selectedEventType)
            .whereEqualTo(FIRESTORE_EVENT_FIELD_HAS_BEEN_APPROVED,true)
            .whereGreaterThan(FIRESTORE_EVENT_FIELD_DATE_START_TIME,startDate)
            .whereLessThan(FIRESTORE_EVENT_FIELD_DATE_START_TIME,endDate)
            .orderBy(FIRESTORE_EVENT_FIELD_DATE_START_TIME, Query.Direction.ASCENDING)
            .limit(limit)
            .startAfter(lastDocument)
            .get()
            .addOnSuccessListener { snapshot ->

                val eventDocuments = snapshot.documents

                if (eventDocuments.isEmpty()) {

                    completion("Event is empty",null, null)

                } else {

                    val lastDocument = snapshot.documents.last()

                    val eventArray = ArrayList<Event>()

                    for (document in eventDocuments) {
                        val eventData = document.data
                        val event = Event(dataEvent = eventData)
                        eventArray.add(event)
                    }

                    completion(null,eventArray, lastDocument)
                }





            }.addOnFailureListener {
                completion(it.localizedMessage,null,null)
            }

    }

我确定我向两个函数都发送了相同的参数，并且最后一个文档也是正确的，它与我的“回收者”视图中显示的最后一个文档完全相同。

但是如果调用第二个功能getAllSearchedEventsAfterLastDocument

，我总是得到空文档

，下面的这一行总是在getAllSearchedEventsAfterLastDocument中触发。

if (eventDocuments.isEmpty()) {
    completion("Event is empty",null, null)
}

请帮助我，我很困惑。

Answer 1

我终于找到了问题，

在.startAfter(lastDocument)

中

lastDocument仍为可空类型（DocumentSnapshot？），应该不会。

为什么在Firestore中使用分页时总是得到空文档

1 个答案: