Flutter Firebase 复杂查询

Question

我有一个复杂的查询要执行。我在我的 Firebase 项目中为此查询添加了一个复合索引。 这是查询。

FirebaseFirestore.instance
              .collection('HouseDetails')
              .where('housePrice', isGreaterThan: GV.price[0].ceil() - 1)
              .where('housePrice', isLessThan: GV.price[1].ceil() + 1)
              .where('houseArea', isGreaterThan: GV.area[0].ceil() - 1)
              .where('houseArea', isLessThan: GV.area[1].ceil() + 1)
              .where('bathrooms',
                  isEqualTo: int.parse(bathrooms.first).ceil() + 1)
              .snapshots();

引发错误

I/flutter ( 9116): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter ( 9116): The following assertion was thrown while handling a gesture:
I/flutter ( 9116): All where filters with an inequality (<, <=, >, or >=) must be on the same field. But you have
I/flutter ( 9116): inequality filters on 'FieldPath([housePrice])' and 'FieldPath([houseArea])'.
I/flutter ( 9116): 'package:cloud_firestore/src/query.dart':
I/flutter ( 9116): Failed assertion: line 484 pos 18: 'hasInequality == field'

阅读文档后，我了解到我无法一次过滤出多个字段类型。但我不明白如何执行需要多个字段进行比较的查询 (housePrice 和 houseArea 在我的例子中）。

如何执行这些查询？

Answer 1

你必须选择一个字段，然后从结果中，你可以过滤另一个字段。

例如，

ModelHouseDetails _requestHouseDetailsFromSnapshot(DocumentSnapshot snapshot) {
return ModelHouseDetails(
    houseId: snapshot.id,
    houseArea: snapshot['houseArea'],
    housePrice: snapshot['housePrice'],
    bathrooms: snapshot['bathrooms']);
}

Stream<List<HouseDetails>> get listHouseDetails {
return FirebaseFirestore.instance.collection('request-service')
      .where('housePrice', isGreaterThan: GV.price[0].ceil() - 1)
      .where('housePrice', isLessThan: GV.price[1].ceil() + 1)
      .snapshots()
      .map((snapshot) =>
      snapshot.docs.where((element) => element['houseArea'] >= GV.area[0].ceil() - 1 && element['houseArea'] <= GV.area[1].ceil() + 1 && element['bathrooms'] == int.parse(bathrooms.first).ceil() + 1).map(_requestHouseDetailsFromSnapshot).toList());
}

Answer 2

我知道这很烦人（我去过那里），但 Firestore 不允许 where 过滤器在不同字段上存在不等式，如文档中所述：

In a compound query, range (<, <=, >, >=) and not equals (!=, not-in) comparisons must all filter on the same field.

您有两种解决方法：

1. 选择一个字段来使用 where 过滤器，然后在客户端执行其余的过滤。以下代码对housePrice 以及服务器端的bathrooms 和客户端的houseArea 执行过滤：

FirebaseFirestore.instance
  .collection('houseDetails')
  .where('housePrice', isGreaterThan: GV.price[0].ceil() - 1)
  .where('housePrice', isLessThan: GV.price[1].ceil() + 1)
  .where('bathrooms', isEqualTo: int.parse(bathrooms.first).ceil() + 1)
  .snapshots()
  // Transform each query snapshot into new stream as list of document snapshots
  .map<List<QueryDocumentSnapshot<Map<String, dynamic>>>>(
  // Discard any document snapshots whose house area data is not in the range
  (querySnapshot) => querySnapshot.docs.where((snapshot) {
    // Try to parse house area as number
    // Note: I don't know house area is a double or int, so I used num for type safety
    final houseArea = num.tryParse(snapshot.data()["houseArea"]);

    // Make sure house area is not null
    if (houseArea != null) {
      // and make sure house area is in the range you specified
      if (houseArea > GV.area[0].ceil() - 1) {
        if (houseArea < GV.area[1].ceil() + 1) {
          // Return true to add the document snapshot to list
          return true;
        }
      }
    }

    // Return false to discard the document snapshot
    return false;
  }).toList(),
);

1. 更改数据模型时考虑复制数据，这是 Firestore 的常见情况。例如，您可以将价格范围为200k-350k的房屋详情存储在一个名为houseDetails-200k-350k的集合中，并对houseArea和bathrooms进行过滤：

FirebaseFirestore.instance
  .collection('houseDetails-200k-350k')
  .where('houseArea', isGreaterThan: GV.area[0].ceil() - 1)
  .where('houseArea', isLessThan: GV.area[1].ceil() + 1)
  .where('bathrooms', isEqualTo: int.parse(bathrooms.first).ceil() + 1)
  .snapshots();