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使用 Cloud Firestore 订购和限制数据

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));order_and_limit.js

Web version 8

citiesRef.orderBy("name").limit(3);test.firestore.js

迅速

注意：此产品不适用于 watchOS 和 App Clip 目标。

citiesRef.order(by: "name").limit(to: 3)ViewController.swift

目标-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

[[citiesRef queryOrderedByField:@"name"] queryLimitedTo:3];ViewController.m

Kotlin+KTX

citiesRef.orderBy("name").limit(3)DocSnippets.kt

Java

citiesRef.orderBy("name").limit(3);DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef.orderBy("name").limit(3);firestore.dart

爪哇

Query query = cities.orderBy("name").limit(3);
Query query = cities.orderBy("name").limitToLast(3);QueryDataSnippets.java

Python

cities_ref = db.collection("cities")
query = cities_ref.order_by("name").limit_to_last(2)
results = query.get()snippets.py

Python

cities_ref = db.collection("cities")
query = cities_ref.order_by("name").limit_to_last(2)
results = await query.get()snippets.py

C++

cities_ref.OrderBy("name").Limit(3);snippets.cpp

节点.js

const firstThreeRes = await citiesRef.orderBy('name').limit(3).get();index.js

去

query := cities.OrderBy("name", firestore.Asc).Limit(3)
query := cities.OrderBy("name", firestore.Asc).LimitToLast(3)query.go

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。

$query = $citiesRef->orderBy('name')->limit(3);query_order_limit.php

统一

Query query = citiesRef.OrderBy("Name").Limit(3);

C＃

Query query = citiesRef.OrderBy("Name").Limit(3);Program.cs

红宝石

query = cities_ref.order("name").limit(3)order_limit_data.rb

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));order_and_limit_desc.js

Web version 8

citiesRef.orderBy("name", "desc").limit(3);test.firestore.js

迅速

注意：此产品不适用于 watchOS 和 App Clip 目标。

citiesRef.order(by: "name", descending: true).limit(to: 3)ViewController.swift

目标-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

[[citiesRef queryOrderedByField:@"name" descending:YES] queryLimitedTo:3];ViewController.m

Kotlin+KTX

citiesRef.orderBy("name", Query.Direction.DESCENDING).limit(3)DocSnippets.kt

Java

citiesRef.orderBy("name", Direction.DESCENDING).limit(3);DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef.orderBy("name", descending: true).limit(3);firestore.dart

爪哇

Query query = cities.orderBy("name", Direction.DESCENDING).limit(3);QueryDataSnippets.java

Python

cities_ref = db.collection(u'cities')
query = cities_ref.order_by(
    u'name', direction=firestore.Query.DESCENDING).limit(3)
results = query.stream()snippets.py

Python

cities_ref = db.collection("cities")
query = cities_ref.order_by("name", direction=firestore.Query.DESCENDING).limit(3)
results = query.stream()snippets.py

C++

cities_ref.OrderBy("name", Query::Direction::kDescending).Limit(3);snippets.cpp

节点.js

const lastThreeRes = await citiesRef.orderBy('name', 'desc').limit(3).get();index.js

去

query := cities.OrderBy("name", firestore.Desc).Limit(3)query.go

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。

$query = $citiesRef->orderBy('name', 'DESC')->limit(3);query_order_desc_limit.php

统一

Query query = citiesRef.OrderByDescending("Name").Limit(3);

C＃

Query query = citiesRef.OrderByDescending("Name").Limit(3);Program.cs

红宝石

query = cities_ref.order("name", "desc").limit(3)order_limit_data.rb

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"));order_multiple.js

Web version 8

citiesRef.orderBy("state").orderBy("population", "desc");test.firestore.js

迅速

注意：此产品不适用于 watchOS 和 App Clip 目标。

citiesRef
    .order(by: "state")
    .order(by: "population", descending: true)ViewController.swift

目标-C

注意：此产品不适用于 watchOS 和 App Clip 目标。

[[citiesRef queryOrderedByField:@"state"] queryOrderedByField:@"population" descending:YES];ViewController.m

Kotlin+KTX

citiesRef.orderBy("state").orderBy("population", Query.Direction.DESCENDING)DocSnippets.kt

Java

citiesRef.orderBy("state").orderBy("population", Direction.DESCENDING);DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef.orderBy("state").orderBy("population", descending: true);firestore.dart

爪哇

Query query = cities.orderBy("state").orderBy("population", Direction.DESCENDING);QueryDataSnippets.java

Python

cities_ref = db.collection(u'cities')
cities_ref.order_by(u'state').order_by(
    u'population', direction=firestore.Query.DESCENDING)snippets.py

Python

cities_ref = db.collection("cities")
cities_ref.order_by("state").order_by(
    "population", direction=firestore.Query.DESCENDING
)snippets.py

C++

cities_ref.OrderBy("state").OrderBy("name", Query::Direction::kDescending);snippets.cpp

节点.js

const byStateByPopRes = await citiesRef.orderBy('state').orderBy('population', 'desc').get();index.js

去

query := client.Collection("cities").OrderBy("state", firestore.Asc).OrderBy("population", firestore.Desc)query.go

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。

$query = $citiesRef->orderBy('state')->orderBy('population', 'DESC');query_order_multi.php

统一

Query query = citiesRef.OrderBy("State").OrderByDescending("Population");

C＃

Query query = citiesRef.OrderBy("State").OrderByDescending("Population");Program.cs

红宝石

query = cities_ref.order("state").order("population", "desc")order_limit_data.rb

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));filter_and_order.js

Web version 8

citiesRef.where("population", ">", 100000).orderBy("population").limit(2);test.firestore.js

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")
    .limit(to: 2)ViewController.swift

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"]
    queryLimitedTo:2];ViewController.m

Kotlin+KTX

citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2)DocSnippets.kt

Java

citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2);DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef
    .where("population", isGreaterThan: 100000)
    .orderBy("population")
    .limit(2);firestore.dart

爪哇

Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population").limit(2);QueryDataSnippets.java

Python

cities_ref = db.collection(u'cities')
query = cities_ref.where(
    u'population', u'>', 2500000).order_by(u'population').limit(2)
results = query.stream()snippets.py

Python

cities_ref = db.collection("cities")
query = cities_ref.where("population", ">", 2500000).order_by("population").limit(2)
results = query.stream()snippets.py

C++

cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000))
    .OrderBy("population")
    .Limit(2);snippets.cpp

节点.js

const biggestRes = await citiesRef.where('population', '>', 2500000)
  .orderBy('population').limit(2).get();index.js

去

query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Desc).Limit(2)query.go

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。

$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('population')
    ->limit(2);query_order_limit_field_valid.php

统一

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population")
    .Limit(2);

C＃

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population")
    .Limit(2);Program.cs

红宝石

query = cities_ref.where("population", ">", 2_500_000).order("population").limit(2)order_limit_data.rb

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"));valid_filter_and_order.js

Web version 8

citiesRef.where("population", ">", 100000).orderBy("population");test.firestore.js

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")ViewController.swift

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"];ViewController.m

Kotlin+KTX

citiesRef.whereGreaterThan("population", 100000).orderBy("population")DocSnippets.kt

Java

citiesRef.whereGreaterThan("population", 100000).orderBy("population");DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef.where("population", isGreaterThan: 100000).orderBy("population");firestore.dart

爪哇

Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population");QueryDataSnippets.java

Python

cities_ref = db.collection(u'cities')
query = cities_ref.where(
    u'population', u'>', 2500000).order_by(u'population')
results = query.stream()snippets.py

Python

cities_ref = db.collection("cities")
query = cities_ref.where("population", ">", 2500000).order_by("population")
results = query.stream()snippets.py

节点.js

citiesRef.where('population', '>', 2500000).orderBy('population');index.js

去

query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Asc)query.go

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。

$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('population');query_order_with_filter.php

统一

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population");

C＃

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population");Program.cs

红宝石

query = cities_ref.where("population", ">", 2_500_000).order("population")order_limit_data.rb

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"));invalid_filter_and_order.js

Web version 8

citiesRef.where("population", ">", 100000).orderBy("country");test.firestore.js

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")ViewController.swift

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"];ViewController.m

Kotlin+KTX

citiesRef.whereGreaterThan("population", 100000).orderBy("country")DocSnippets.kt

Java

citiesRef.whereGreaterThan("population", 100000).orderBy("country");DocSnippets.java

Dart

final citiesRef = db.collection("cities");
citiesRef.where("population", isGreaterThan: 100000).orderBy("country");firestore.dart

爪哇

Query query = cities.whereGreaterThan("population", 2500000L).orderBy("country");QueryDataSnippets.java

Python

cities_ref = db.collection(u'cities')
query = cities_ref.where(u'population', u'>', 2500000).order_by(u'country')
results = query.stream()snippets.py

Python

cities_ref = db.collection("cities")
query = cities_ref.where("population", ">", 2500000).order_by("country")
results = query.stream()snippets.py

C++

// BAD EXAMPLE -- will crash the program:
cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000))
    .OrderBy("country");snippets.cpp

节点.js

citiesRef.where('population', '>', 2500000).orderBy('country');index.js

去

// Note: This is an invalid query. It violates the constraint that range
// and order by are required to be on the same field.
query := cities.Where("population", ">", 2500000).OrderBy("country", firestore.Asc)query.go

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。

$invalidRangeQuery = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('country');query_order_field_invalid.php

统一

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Country");

C＃

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Country");Program.cs

红宝石

query = cities_ref.where("population", ">", 2_500_000).order("country")order_limit_data.rb

您不能按相等 ( = ) 或子句in包含的任何字段对查询进行排序。