[英]Count number of documents with a particular field in a collection Firestore Flutter
[英]Get Firestore documents with a field that is equal to a particular string in flutter
我正在尝试获取集合中具有等于特定字符串的特定字段的文档。 我正在建立一个 POS,我想获得特定城市的所有销售额。
final FirebaseFirestore _firestore = FirebaseFirestore.instance;
final CollectionReference _mainCollection = _firestore.collection('Sales');
Stream<QuerySnapshot> readFeeds() {
CollectionReference notesItemCollection =
_mainCollection.where('seller_location', isEqualTo: "London").get();
return notesItemCollection.snapshots();
}
我收到此错误:
不能将“Future<QuerySnapshot<Object?>>”类型的值分配给“CollectionReference<Object?>”类型的变量。
我已将 added cast as CollectionReference<Object?>;
但查询仍然无效。 这就是我访问数据的方式:
@override
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
stream: readFeeds(),
builder: (context, snapshot) {
if (snapshot.hasError) {
return Text('Something went wrong');
} else if (snapshot.hasData || snapshot.data != null) {
return ListView.separated(
separatorBuilder: (context, index) => SizedBox(height: 16.0),
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) {
var noteInfo = snapshot.data!.docs[index];
String docID = snapshot.data!.docs[index].id;
String name = noteInfo['name'].toString();
String price = noteInfo['price'].toString();
String quantity = noteInfo['quantity'].toString();
return Ink(
decoration: BoxDecoration(
color: CustomColors.firebaseGrey.withOpacity(0.1),
borderRadius: BorderRadius.circular(8.0),
),
child: ListTile(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(8.0),
),
onTap: () => Navigator.of(context).push(
MaterialPageRoute(
builder: (context) => EditScreen(
documentId: docID,
currentName: name,
currentPrice: price,
currentQuantity: quantity,
),
),
),
title: Text(
name,
maxLines: 1,
overflow: TextOverflow.ellipsis,
style: TextStyle(color: Colors.white),
),
),
);
},
);
}
return Center(
child: CircularProgressIndicator(
valueColor: AlwaysStoppedAnimation<Color>(
CustomColors.firebaseOrange,
),
),
);
},
);
}
}
您收到以下错误:
不能将“Future<QuerySnapshot<Object?>>”类型的值分配给“CollectionReference<Object?>”类型的变量。
因为下面一行代码:
CollectionReference notesItemCollection =
_mainCollection.where('seller_location', isEqualTo: "London").get();
这是有道理的,因为get() function 返回一个Future而不是CollectionReference object。在 Dart 中没有办法创建这样的转换,因此出现错误。
由于您使用的是where() function,因此返回的 object 的类型是Query 。 所以你的代码应该是这样的:
Query queryBySellerLocation =
_mainCollection.where('seller_location', isEqualTo: "London");
正确定义此查询后,您可以执行 get() 调用并收集结果:
queryBySellerLocation.get().then(...);
如果有帮助,请试试这个。
QuerySnapshot<Map<String,dynamic>>readFeeds() {
QuerySnapshot<Map<String,dynamic>>response=await _mainCollection.where('seller_location', isEqualTo: "London").get()
return response;
}
你可以像这样访问这些数据
response.docs.forEach((element) {
///this is Map<String,dynamic>
element.data();
});
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.