如何在 Firebase Firestore 中查询 Flutter 中 Geopoint 类型的字段？

Question

I am querying a firestore collection for documents inside of a latitude and longitude range. Since it appears you can't conduct a query with arguments given to two different fields ('lat', 'lon'), I have assigned a type Geopoint to a single field 'coords' that has the longitude and latitude. How do I use.where() with geopoints? Below is the general query I would like to use, where _latMin, _latMax, etc. are variables linked to the bounding box of my map.

_getDocs() async {
  print('getdocs');
  final QuerySnapshot snapshot = await FirebaseFirestore.instance
      .collection('collectionName')
      .where(
        'coords',
        isGreaterThan: _latMin,
        isLessThan: _latMax,
      )
      .where(
        'coords',
        isGreaterThan: _lonMin,
        isLessThan: _lonMax,
      )
      .get();
  snapshot.docs.forEach((DocumentSnapshot doc) {
    print(doc.data());
  });
}

How Do I reference the latitude and longitude inside of coords?

Answer 1

A Firestore query can only contain range conditions ( > , >= , etc) on one value. So you can filter on either the latitude or longitude of the coords , but not on both in a single query.

If you want to perform geoqueries on Firestore at the moment, the common approach is to store an additional so-called geohash value in your document, which is a (rather magical) string value that combines latitude and longitude in a way that allows you to query them to filter on geographic blocks.

If you want to learn how this works, I recommend checking out this video on the topic: Querying Firebase and Firestore based on geographic location or distance .

If you want to implement this approach on top of Firestore, check out the documentation onimplementing geoqueries on Firestore .

I also recommend checking out these previous questions on the topic:

• How to run a geo "nearby" query with firestore?
• How to filter Firestore collection data using function (for location distance filtering)
• Is there a way to use GeoFire with Firestore?
• Firestore multiple range query