无法从 Firestore 获取时间戳文档字段

Question

When getting data from Firestore, I am unable to get a timestamp field.

My Room document is structured like this:

and I'm getting the rooms from Firestore like below.

Helper class:

    fun getRooms(userId: String): Task<QuerySnapshot> {
        return FirebaseFirestore.getInstance()
                .collection(KEY_USERS).document(userId)
                .collection(KEY_ROOMS).get()
    }

Interactor class:

private fun getRooms(): Task<List<Room>> {
    val source = TaskCompletionSource<List<Room>>()
    val listener = OnCompleteListener<QuerySnapshot> {
        if (it.isSuccessful) {
            val roomSnapshots = it.result
            if (!roomSnapshots.isEmpty) {
                val rooms = ArrayList<Room>()
                for (roomSnapshot in roomSnapshots) {
                    rooms.add(Room(roomSnapshot))
                }
                source.setResult(rooms)
            }
        } else {
            source.setException(it.exception!!)
        }
    }
    FirebaseFireStoreHelper.getRooms(mUserId).addOnCompleteListener(listener)
    return source.task
}

My Room model class:

class Room(document: DocumentSnapshot) {

    companion object {
        private const val KEY_DATE_CREATED = "dateCreated"
        private const val KEY_TITLE = "title"
    }

    private lateinit var mId: String
    private lateinit var mDateCreated: Date
    private lateinit var mTitle: String

    init {
        if (document.exists()) {
            mId = document.id
            mDateCreated = document.getDate(KEY_DATE_CREATED)!!
            mTitle = document.getString(KEY_TITLE)!!
        }
    }

    fun getId(): String = mId

    fun getDateCreated(): Date? = mDateCreated

    fun getTitle(): String = mTitle

}

The issue is that document.getDate(KEY_DATE_CREATED) is always returning null . I've tried using get(KEY_DATE_CREATED) and getString(KEY_DATE_CREATED) just to see if I could get any value, but to no avail.

After a few more tries, I tested printing out the whole object and was able to get this:

DocumentSnapshot{
    key=users/kCKkmgLmLGfvbPFK09qyZ5uoyw32/rooms/R35Bj56rda7pkkYWH1MQ,
    metadata=SnapshotMetadata{
        hasPendingWrites=false,
        isFromCache=false
    },
    doc=Document{
        key=users/kCKkmgLmLGfvbPFK09qyZ5uoyw32/rooms/R35Bj56rda7pkkYWH1MQ,
        data=zza{
            (title=>Sample Room)
        };,
    version=SnapshotVersion(seconds=1523285961, nanos=350799000),
    hasLocalMutations=false
    }
}

So apparently, the dateCreated field is not being retrieved in the first place, which explains the null value. From the code I have, I believe I'm handling the parsing properly. What's confusing is I also have a Message object that has a dateCreated timestamp field and I'm able to get it properly.

PS: The sample codes are in Kotlin, I could post a Java code version if it could help make things more clear.

---

Update: Here's a screenshot of the Message document from Firestore.

And here's the my Message model class:

class Message(document: DocumentSnapshot) {

    companion object {
        private const val KEY_CONTENT = "content"
        private const val KEY_DATE_CREATED = "dateCreated"
    }

    private lateinit var mId: String
    private lateinit var mContent: String
    private lateinit var mDateCreated: Date

    // TODO: Figuring out why getDate doesn't seem to work for Rooms

    init {
        if (document.exists()) {
            mId = document.id
            mContent = document.getString(KEY_CONTENT)!!
            mDateCreated = document.getDate(KEY_DATE_CREATED)!!
        }
    }

    fun getId(): String = mId

    fun getContent(): String = mContent

    fun getDateCreated(): Date = mDateCreated

    fun getStringFormattedDateCreated() = FormatterUtil.getFormattedTimestamp(mDateCreated)

}

Making the Date nullable ( ? ) for Room does nothing.

Answer 1

Seems that is not parsing correctly the format of the date.

With firebase what I am doing is convert the date in to an Unix timestamp value, store that value in firebase. You can do that with the method getTime().

And when I retrieve the data, the same, I convert the Unix timestamp value to a type Date.

Date date = new Date((long)timeStamp*1000);

Ex:

Data ------> Unix timestamp

05/14/2018 @ 3:26pm (UTC) ------ > 1526311610

Answer 2

If I have understood this problem correctly then you'll need to set the snapshot options, or it could be you're not waiting for the full result.

I use the Node.js platform so you'll need to do the equivalent for your SDK.

If set, controls the return value for server timestamps that have not yet been set to their final value.

By specifying 'estimate', pending server timestamps return an estimate based on the local clock. This estimate will differ from the final value and cause these values to change once the server result becomes available.

By specifying 'previous', pending timestamps will be ignored and return their previous value instead.

If omitted or set to 'none', null will be returned by default until the server value becomes available

Here is the link to the Node.js Client SDK. This may help you in the right direction. https://firebase.google.com/docs/reference/js/firebase.firestore.SnapshotOptions

Answer 3

First, you need to keep the names on your POJO item with the same ones of your Database, all your POJOs in the examples are wrote with camelCase annotation and in your database it is not.

If you want to keep your model with camelCase and your database without, you can use the annotation PropertyName :

data class myFancyPojo(@PropertyName("name") val mName: String = "",
                   @ServerTimestamp
                   @PropertyName("timestamp")
                   val mTimestamp: Date? = null)

You missed the annotation @ServerTimestamp on your parameter in the POJO builder, which marks it it be inflated from a server timestamp.

Annotation used to mark a Date field to be populated with a server timestamp. If a POJO being written contains null for a @ServerTimestamp-annotated field, it will be replaced with a server-generated timestamp.

https://firebase.google.com/docs/reference/android/com/google/firebase/firestore/ServerTimestamp

Finally, don't forget that if you are writing your code in Java you should keep an empty constructor, and if you are writing it on Kotlin you should give a default value to any parameter of the class.

Answer 4

When getting timeStamp from document you can use this.

Object ob=document.getDate("createdDate", DocumentSnapshot.ServerTimestampBehavior.ESTIMATE);

And Then> ob.toString();