如何从Firestore获取对象数组 [英] How to get an Array of Objects from Firestore
问题描述
查询作为地图数组的字段的正确方法是什么。
What would be the right way to query a field that is an array of maps.
目前结构是
Collection1
Document1
-papers: <---- This is an array
(0):
-Name:abc
-Id:123
(1):
-Name:xyz
-Id:456
这是我的代码
DocumentReference docRef = db.collection("Collection1").document("Document1");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
public void onComplete(@NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document != null && document.exists()) {
//?? how can I retrieve papers
}
}
});
我基本上检索它并将其转换为ArrayList>然后循环遍历它以创建我的最终版本ArrayList?
Basically do I retrieve it and cast it as an ArrayList> and then loop through it to create my final ArrayList ?
或者它是如何工作的?
推荐答案
按照有关阵列的官方文档:
虽然Cloud Firestore可以存储数组,
但它不支持
查询数组成员或更新单个数组元素。
Although Cloud Firestore can store arrays,
it does not support
querying array members or updating single array elements.
如果您只想获得整个论文
数组,则需要迭代 Map
,如下所示:
If you only want to get the entire papers
array you need to iterate over a Map
like this:
Map<String, Object> map = document.getData();
for (Map.Entry<String, Object> entry : map.entrySet()) {
if (entry.getKey().equals("papers")) {
Log.d("TAG", entry.getValue().toString());
}
}
但请注意,即使论文
对象作为数组存储在数据库中, entry.getValue()
返回 ArrayList
,而不是数组
。
But note, even if papers
object is stored in the database as an array, entry.getValue()
returns an ArrayList
, not an array
.
编辑2018年8月13日:
根据有关数组成员资格,现在可以使用 whereArrayContains()
方法根据数组值过滤数据。一个简单的例子是:
According to the updated documentation regarding array membership, now it is possible to filter data based on array values using whereArrayContains()
method. A simple example would be:
CollectionReference citiesRef = db.collection("cities");
citiesRef.whereArrayContains("regions", "west_coast");
此查询返回每个城市文档,其中regions字段是一个数组包含west_coast。如果数组具有您查询的值的多个实例,则文档仅包含在结果中一次。
This query returns every city document where the regions field is an array that contains west_coast. If the array has multiple instances of the value you query on, the document is included in the results only once.
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