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使用 Cloud Firestore 訂購和限制數據

Cloud Firestore 提供了強大的查詢功能，用於指定您要從集合中檢索哪些文檔。這些查詢也可以與get()或addSnapshotListener()一起使用，如獲取數據中所述。

訂單和限制數據

默認情況下，查詢會按文檔 ID 升序檢索滿足查詢的所有文檔。您可以使用orderBy()指定數據的排序順序，並且可以使用limit()限制檢索的文檔數量。如果您指定limit() ，則該值必須大於或等於零。

例如，您可以按字母順序查詢前 3 個城市：

Web modular API

import { query, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, orderBy("name"), limit(3));order_and_limit.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

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

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[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

節點.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

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

您還可以按降序排序以獲得最後3 個城市：

Web modular API

import { query, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, orderBy("name", "desc"), limit(3));order_and_limit_desc.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

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

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[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('cities')
query = cities_ref.order_by(
    '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

節點.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

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

您還可以按多個字段排序。例如，如果您想按州排序，並在每個州內按人口降序排序：

Web modular API

import { query, orderBy } from "firebase/firestore";  

const q = query(citiesRef, orderBy("state"), orderBy("population", "desc"));order_multiple.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

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

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[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('cities')
cities_ref.order_by('state').order_by(
    '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

節點.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

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

您可以將where()過濾器與orderBy()和limit()結合使用。在下面的例子中，查詢定義了一個人口閾值，按人口升序排序，只返回前幾個超過閾值的結果：

Web modular API

import { query, where, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, where("population", ">", 100000), orderBy("population"), limit(2));filter_and_order.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "population")
    .limit(to: 2)ViewController.swift

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[[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('cities')
query = cities_ref.where(
    'population', '>', 2500000).order_by('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

節點.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

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

但是，如果您有一個具有範圍比較（ < 、 <= 、 > 、 >= ）的過濾器，您的第一次排序必須在同一字段上，請參閱下面的orderBy()限制列表。

限制

請注意orderBy()子句的以下限制：

orderBy()子句還過濾是否存在給定字段。結果集將不包括不包含給定字段的文檔。

如果您包含一個帶有範圍比較的過濾器（ < 、 <= 、 > 、 >= ），您的第一個排序必須在同一個字段上：

有效：同一字段上的範圍過濾器和orderBy

Web modular API

import { query, where, orderBy } from "firebase/firestore";  

const q = query(citiesRef, where("population", ">", 100000), orderBy("population"));valid_filter_and_order.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "population")ViewController.swift

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[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('cities')
query = cities_ref.where(
    'population', '>', 2500000).order_by('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

節點.js

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

去

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

PHP

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

無效：不同字段上的範圍過濾器和一階orderBy

Web modular API

import { query, where, orderBy } from "firebase/firestore";  

const q = query(citiesRef, where("population", ">", 100000), orderBy("country"));invalid_filter_and_order.js

Web namespaced API

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

迅速

注意：此產品不適用於 watchOS 和 App Clip 目標。

citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "country")ViewController.swift

目標-C

注意：此產品不適用於 watchOS 和 App Clip 目標。

[[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('cities')
query = cities_ref.where('population', '>', 2500000).order_by('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

節點.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

有關安裝和創建 Cloud Firestore 客戶端的更多信息，請參閱Cloud Firestore 客戶端庫。

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

統一

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

C＃

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

紅寶石

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

您不能按相等 ( = ) 或in中包含的任何字段對查詢進行排序。

`orderBy`和存在

當您按給定字段對查詢進行排序時，查詢只能返回存在排序字段的文檔。

例如，以下查詢不會返回任何未設置population字段的文檔，即使它們符合查詢過濾器。

爪哇

db.collection("cities").whereEqualTo("country", “USA”).orderBy(“population”);

一個相關的影響適用於不平等。在字段上使用不等式過濾器的查詢也意味著按該字段排序。以下查詢不會返回沒有population字段的文檔，即使該文檔中的country = USA也是如此。作為解決方法，您可以為每個排序執行單獨的查詢，或者您可以為您排序所依據的所有字段分配一個值。

爪哇

db.collection(“cities”).where(or(“country”, USA”), greaterThan(“population”, 250000));

上面的查詢包含對不等式的隱含排序，等同於以下內容：

爪哇

db.collection(“cities”).where(or(“country”, USA”), greaterThan(“population”, 250000)).orderBy(“population”);