如何將聚合資料從Firestore檔案映射回Kotlin串列

想使用 Firestore 減少我的應用程式中的讀取次數。所以我在我的集??合中創建了一個具有以下結構的檔案來保存 10 個“記錄”的值，我將通過一次讀取獲得 - 因為這個檔案的大小相當不錯，不用擔心單個檔案的 1MB 限制大小檔案。我正在使用云功能更新本檔案的內容。

name of collection: helperz
name of document: top10
field name in top10: tresholdCounter - this I need to check if a single map should be added to top10 or not
field name in top10: top10 . . array of maps


helperz/top10/tresholdCounter
helperz/top10/top10/0/author
helperz/top10/top10/0/name
helperz/top10/top10/0/url
helperz/top10/top10/1/author
helperz/top10/top10/1/name
helperz/top10/top10/1/url
helperz/top10/top10/2/author
helperz/top10/top10/2/name
helperz/top10/top10/2/url
helperz/top10/top10/3/author
helperz/top10/top10/3/name
helperz/top10/top10/3/url
helperz/top10/top10/4/author
helperz/top10/top10/4/name
helperz/top10/top10/4/url
..
helperz/top10/top10/10/author
helperz/top10/top10/10/name
helperz/top10/top10/10/url

我有一個資料類。. 像這樣：

data class MyClass(
    var name: String? = null,
    var url: String? = null,
    var author: String? = null,
    var counter: Int = 0,
    var free: Boolean? = false,
    var global: Boolean?=true,
    var poses: ArrayList<MyPoze>? = null,
    var docId: string? = null,
    var category: ArrayList<String>? = null,
    @get:PropertyName(CREATED)
    @set:PropertyName(CREATED)
    @ServerTimestamp var created: Timestamp? = null
    )

還有一些其他領域，但對于這個問題，應該沒問題。

我有一個從 Firestore 檢索資料的代碼（在我的 viewModel 中）：

private fun getHelperzTop10() = viewModelScope.launch {
    Log.d("MP23", "getHelperzTop10")
    val docRef = db.collection("helperz").document("top10")

    docRef.addSnapshotListener { snapshot, e ->
        if (e != null) {
            Log.w("MP23", "Listen failed.", e)
            return@addSnapshotListener
        }

        if (snapshot != null && snapshot.exists()) {
            val docSize = firestoreDocument.getSize(snapshot);
            Log.d("MP23","docSize in Bytes: $docSize, in KB: ${docSize * 0.001}, in MB: ${docSize * 0.000001}"
            )
            val top10 = snapshot.data
            Log.d("MP23", top10!!::class.simpleName.toString() )

            if ("top10" in keys) {
                val top10arr = top10["top10"] as ArrayList<MyClass>
                Log.d("MP23", "we have top10 in top10")
                Log.d("MP23", top10arr!!::class.simpleName.toString())
                Log.d("MP23", top10arr.toString())
            //// ?? PROBLEM HERE ///                
            // here I need somehow to cast this array of maps as MyClass, but I am getting error:
            // java.util.ArrayList cannot be cast to java.lang.MyClass
            // or
            // java.util.ArrayList cannot be cast to java.lang.Object[] - with some other versions
            }
        } else {
            Log.d("MP23", "Current data: null")
        }
    }
}

如果有人可以建議我如何將結果轉換為 MyClass，那就太好了。在正常情況下（我有我查詢的檔案）作為單個檔案，我可以輕松地做到：

val singleRec = singleRec.toObject(MyClass::class.java)

uj5u.com熱心網友回復：

如果您想將top10陣列作為List<MyClass>，我能想到的最簡單的解決方案是創建另一個類：

data class Document(
    var top10: MutableList<MyClass>? = null
)

并像這樣閱讀檔案的內容：

docRef.get().addOnCompleteListener {
    if (it.isSuccessful) {
        val snapshot = it.result
        snapshot?.let {
            val document = snapshot.toObject(Document::class.java)
            document?.let {
                val top10 = document.top10
                top10?.let {
                    for (myClass in top10) {
                        val name =  myClass.name
                        Log.d("TAG", "$name")
                    }
                }
            }
        }
    } else {
        it.exception?.message?.let { message ->
            Log.d("TAG", message) //Never ignore potential errors!   
        }
    }
}

我還建議您閱讀以下資源以更好地理解：

• 如何將物件陣列從 Cloud Firestore 映射到物件串列？

標籤：Google Cloud Collective 安卓火力基地科特林谷歌云平台谷歌云火库

上一篇：按下后退按鈕時處理前一個片段的onViewCreated()

下一篇：如何訪問Context以在JetpackCompose中創建檔案目錄？