Cloud Firestore 提供了强大的查询功能,用于指定您要从集合中检索哪些文档。这些查询也可以与get()
或addSnapshotListener()
一起使用,如获取数据中所述。
订单和限制数据
默认情况下,查询会按文档 ID 升序检索满足查询的所有文档。您可以使用orderBy()
指定数据的排序顺序,并且可以使用limit()
检索的文档数量。
例如,您可以按字母顺序查询前 3 个城市:
Web version 9
import { query, orderBy, limit } from "firebase/firestore"; const q = query(citiesRef, orderBy("name"), limit(3));
Web version 8
citiesRef.orderBy("name").limit(3);
迅速
citiesRef.order(by: "name").limit(to: 3)
目标-C
[[citiesRef queryOrderedByField:@"name"] queryLimitedTo:3];
Kotlin+KTX
citiesRef.orderBy("name").limit(3)
Java
citiesRef.orderBy("name").limit(3);
Dart
final citiesRef = db.collection("cities"); citiesRef.orderBy("name").limit(3);
爪哇
Python
Python
C++
cities_ref.OrderBy("name").Limit(3);
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef.OrderBy("Name").Limit(3);
C#
红宝石
您还可以按降序排序以获得最后3 个城市:
Web version 9
import { query, orderBy, limit } from "firebase/firestore"; const q = query(citiesRef, orderBy("name", "desc"), limit(3));
Web version 8
citiesRef.orderBy("name", "desc").limit(3);
迅速
citiesRef.order(by: "name", descending: true).limit(to: 3)
目标-C
[[citiesRef queryOrderedByField:@"name" descending:YES] queryLimitedTo:3];
Kotlin+KTX
citiesRef.orderBy("name", Query.Direction.DESCENDING).limit(3)
Java
citiesRef.orderBy("name", Direction.DESCENDING).limit(3);
Dart
final citiesRef = db.collection("cities"); citiesRef.orderBy("name", descending: true).limit(3);
爪哇
Python
Python
C++
cities_ref.OrderBy("name", Query::Direction::kDescending).Limit(3);
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef.OrderByDescending("Name").Limit(3);
C#
红宝石
您还可以按多个字段排序。例如,如果您想按州排序,并在每个州内按人口降序排序:
Web version 9
import { query, orderBy } from "firebase/firestore"; const q = query(citiesRef, orderBy("state"), orderBy("population", "desc"));
Web version 8
citiesRef.orderBy("state").orderBy("population", "desc");
迅速
citiesRef .order(by: "state") .order(by: "population", descending: true)
目标-C
[[citiesRef queryOrderedByField:@"state"] queryOrderedByField:@"population" descending:YES];
Kotlin+KTX
citiesRef.orderBy("state").orderBy("population", Query.Direction.DESCENDING)
Java
citiesRef.orderBy("state").orderBy("population", Direction.DESCENDING);
Dart
final citiesRef = db.collection("cities"); citiesRef.orderBy("state").orderBy("population", descending: true);
爪哇
Python
Python
C++
cities_ref.OrderBy("state").OrderBy("name", Query::Direction::kDescending);
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef.OrderBy("State").OrderByDescending("Population");
C#
红宝石
您可以将where()
过滤器与orderBy()
和limit()
结合使用。在下面的例子中,查询定义了一个人口阈值,按人口升序排序,只返回前几个超过阈值的结果:
Web version 9
import { query, where, orderBy, limit } from "firebase/firestore"; const q = query(citiesRef, where("population", ">", 100000), orderBy("population"), limit(2));
Web version 8
citiesRef.where("population", ">", 100000).orderBy("population").limit(2);
迅速
citiesRef .whereField("population", isGreaterThan: 100000) .order(by: "population") .limit(to: 2)
目标-C
[[[citiesRef queryWhereField:@"population" isGreaterThan:@100000] queryOrderedByField:@"population"] queryLimitedTo:2];
Kotlin+KTX
citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2)
Java
citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2);
Dart
final citiesRef = db.collection("cities"); citiesRef .where("population", isGreaterThan: 100000) .orderBy("population") .limit(2);
爪哇
Python
Python
C++
cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000)) .OrderBy("population") .Limit(2);
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef .WhereGreaterThan("Population", 2500000) .OrderBy("Population") .Limit(2);
C#
红宝石
但是,如果您有一个具有范围比较( <
、 <=
、 >
、 >=
)的过滤器,您的第一次排序必须在同一字段上,请参阅下面的orderBy()
限制列表。
限制
请注意orderBy()
子句的以下限制:
-
orderBy()
子句还过滤给定字段的存在。结果集将不包括不包含给定字段的文档。 如果您包含一个带有范围比较(
<
、<=
、>
、>=
)的过滤器,您的第一个排序必须在同一个字段上:有效:同一字段上的范围过滤器和
orderBy
Web version 9
import { query, where, orderBy } from "firebase/firestore"; const q = query(citiesRef, where("population", ">", 100000), orderBy("population"));
Web version 8
citiesRef.where("population", ">", 100000).orderBy("population");
迅速
注意:此产品不适用于 watchOS 和 App Clip 目标。citiesRef .whereField("population", isGreaterThan: 100000) .order(by: "population")
目标-C
注意:此产品不适用于 watchOS 和 App Clip 目标。[[citiesRef queryWhereField:@"population" isGreaterThan:@100000] queryOrderedByField:@"population"];
Kotlin+KTX
citiesRef.whereGreaterThan("population", 100000).orderBy("population")
Java
citiesRef.whereGreaterThan("population", 100000).orderBy("population");
Dart
final citiesRef = db.collection("cities"); citiesRef.where("population", isGreaterThan: 100000).orderBy("population");
爪哇
Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population");
Python
Python
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef .WhereGreaterThan("Population", 2500000) .OrderBy("Population");
C#
红宝石
无效:不同字段上的范围过滤器和一
orderBy
Web version 9
import { query, where, orderBy } from "firebase/firestore"; const q = query(citiesRef, where("population", ">", 100000), orderBy("country"));
Web version 8
citiesRef.where("population", ">", 100000).orderBy("country");
迅速
注意:此产品不适用于 watchOS 和 App Clip 目标。citiesRef .whereField("population", isGreaterThan: 100000) .order(by: "country")
目标-C
注意:此产品不适用于 watchOS 和 App Clip 目标。[[citiesRef queryWhereField:@"population" isGreaterThan:@100000] queryOrderedByField:@"country"];
Kotlin+KTX
citiesRef.whereGreaterThan("population", 100000).orderBy("country")
Java
citiesRef.whereGreaterThan("population", 100000).orderBy("country");
Dart
final citiesRef = db.collection("cities"); citiesRef.where("population", isGreaterThan: 100000).orderBy("country");
爪哇
Python
Python
C++
// BAD EXAMPLE -- will crash the program: cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000)) .OrderBy("country");
节点.js
去
PHP
PHP
有关安装和创建 Cloud Firestore 客户端的更多信息,请参阅Cloud Firestore 客户端库。
统一
Query query = citiesRef .WhereGreaterThan("Population", 2500000) .OrderBy("Country");
C#
红宝石
- 您不能按相等 (
=
) 或子句in
包含的任何字段对查询进行排序。