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指定要返回的文档

Overview

在本指南中，您可以学习；了解如何使用以下方法指定从读取操作中返回哪些文档：

limit()：指定从查询中返回的最大文档数。
sort()：指定返回文档的排序顺序。
skip()：指定在返回查询结果之前要跳过的文档数。

样本数据

本指南中的示例使用 Atlas示例数据集中的sample_restaurants.restaurants集合。要学习；了解如何创建免费的MongoDB Atlas 群集并加载示例数据集，请参阅 PyMongo入门教程。

Limit

要指定读取操作返回的最大文档数，请调用limit()方法。

以下示例查找 cuisine字段值为 "Italian" 的所有餐厅，并将结果限制为 5 文档。选择 Synchronous 或 Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}).limit(5)
for restaurant in results:
    print(restaurant["name"])

Isle Of Capri Resturant Italian
Arturo'S Italian
Patsy'S Italian Restaurant Italian
Piccola Venezia Italian
Roadhouse Restaurant Italian

results = restaurants.find({ "cuisine" : "Italian"}).limit(5)
async for restaurant in results:
    print(restaurant["name"])

Isle Of Capri Resturant Italian
Arturo'S Italian
Patsy'S Italian Restaurant Italian
Piccola Venezia Italian
Roadhouse Restaurant Italian

您还可以通过在 find() 方法中指定 limit 参数来限制返回的文档数量。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}, limit=5)
for restaurant in results:
    print(restaurant["name"])

Isle Of Capri Resturant Italian
Arturo'S Italian
Patsy'S Italian Restaurant Italian
Piccola Venezia Italian
Roadhouse Restaurant Italian

results = restaurants.find({ "cuisine" : "Italian"}, limit=5)
async for restaurant in results:
    print(restaurant["name"])

Isle Of Capri Resturant Italian
Arturo'S Italian
Patsy'S Italian Restaurant Italian
Piccola Venezia Italian
Roadhouse Restaurant Italian

提示

前面的示例返回查询返回的前五个文档（排名不分先后）。以下部分介绍如何按指定的排序顺序返回文档。

Sort

要按指定顺序返回文档，请调用sort()方法。 sort()方法接受两个参数：对结果进行排序的字段和排序方向。要指定排序方向，请指定pymongo.ASCENDING或pymongo.DESCENDING 。 ASCENDING将值从最低到最高排序， DESCENDING将值从最高到最低排序。如果未指定任一方向，则该方法默认按升序排序。

以下示例返回 cuisine 值为 "Italian" 的所有文档，并按升序排序。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}).sort("name", pymongo.ASCENDING)
for restaurant in results:
    print(restaurant["name"])

(Lewis Drug Store) Locanda Vini E Olii
101 Restaurant And Bar
44 Sw Ristorante & Bar
900 Park
A Voce
...
Zucchero E Pomodori

results = restaurants.find({ "cuisine" : "Italian"}).sort("name", pymongo.ASCENDING)
async for restaurant in results:
    print(restaurant["name"])

(Lewis Drug Store) Locanda Vini E Olii
101 Restaurant And Bar
44 Sw Ristorante & Bar
900 Park
A Voce
...
Zucchero E Pomodori

您还可以通过在 find() 方法中指定 sort 参数来对文档进行排序。以下示例指定 sort 参数，以按照与上一示例相同的顺序返回结果。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}, sort={"name": pymongo.ASCENDING} )
for restaurant in results:
    print(restaurant["name"])

(Lewis Drug Store) Locanda Vini E Olii
101 Restaurant And Bar
44 Sw Ristorante & Bar
900 Park
A Voce
...
Zucchero E Pomodori

results = restaurants.find({ "cuisine" : "Italian"}, sort={"name": pymongo.ASCENDING} )
async for restaurant in results:
    print(restaurant["name"])

(Lewis Drug Store) Locanda Vini E Olii
101 Restaurant And Bar
44 Sw Ristorante & Bar
900 Park
A Voce
...
Zucchero E Pomodori

跳过

要在返回查询结果之前跳过指定数量的文档，请调用skip()方法并传入要跳过的文档数。 skip()方法会忽略查询结果中指定数量的文档并返回其余文档。

以下示例返回 borough字段值为 "Manhattan" 的所有文档，并跳过前 10 个文档。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "borough" : "Manhattan"}, skip=10)
for restaurant in results:
    print(restaurant["name"])

Dorrian'S Red Hand Restaurant
The Princeton Club
Moran'S Chelsea
La Parisienne Diner
Jimmy'S Corner
...

results = restaurants.find({ "borough" : "Manhattan"}, skip=10)
async for restaurant in results:
    print(restaurant["name"])

Dorrian'S Red Hand Restaurant
The Princeton Club
Moran'S Chelsea
La Parisienne Diner
Jimmy'S Corner
...

您还可以使用 find() 方法的 skip 参数跳过返回的文档。以下示例指定了与前面的示例相同的 skip。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "borough" : "Manhattan"}, skip=10)
for restaurant in results:
    print(restaurant["name"])

Dorrian'S Red Hand Restaurant
The Princeton Club
Moran'S Chelsea
La Parisienne Diner
Jimmy'S Corner
...

results = restaurants.find({ "borough" : "Manhattan"}, skip=10)
async for restaurant in results:
    print(restaurant["name"])

Dorrian'S Red Hand Restaurant
The Princeton Club
Moran'S Chelsea
La Parisienne Diner
Jimmy'S Corner
...

组合限制、排序和跳过

您可以在单个操作中组合使用limit() 、 sort()和skip()方法。这允许您设置要返回的最大排序文档数，在返回之前跳过指定数量的文档。

以下示例返回 cuisine 值为 "Italian" 的文档。结果按字母顺序排序，跳过前 10 个文档。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}) \
                     .sort("name", pymongo.ASCENDING) \
                     .limit(5) \
                     .skip(10)
for restaurant in results:
    print(restaurant["name"])

Acqua
Acqua Restaurant
Acqua Santa
Acquista Trattoria
Acquolina Catering

results = restaurants.find({ "cuisine" : "Italian"}) \
                     .sort("name", pymongo.ASCENDING) \
                     .limit(5) \
                     .skip(10)
async for restaurant in results:
    print(restaurant["name"])

Acqua
Acqua Restaurant
Acqua Santa
Acquista Trattoria
Acquolina Catering

注意

调用这些方法的顺序不会更改返回的文档。驾驶员会自动对调用重新排序，以首先执行排序和跳过操作，然后执行限制操作。

您还可以在 find() 方法中将结果指定为参数，从而对结果进行限制、排序和跳过。以下示例指定与前面的示例相同的查询。选择Synchronous或Asynchronous标签页以查看相应的代码：

results = restaurants.find({ "cuisine" : "Italian"}, limit=5, sort={"name": pymongo.ASCENDING}, skip=10)
for restaurant in results:
    print(restaurant["name"])

Acqua
Acqua Restaurant
Acqua Santa
Acquista Trattoria
Acquolina Catering

results = restaurants.find({ "cuisine" : "Italian"}, limit=5, sort={"name": pymongo.ASCENDING}, skip=10)
async for restaurant in results:
    print(restaurant["name"])

Acqua
Acqua Restaurant
Acqua Santa
Acquista Trattoria
Acquolina Catering

指定要返回的文档

Overview

样本数据

Limit

提示

Sort

跳过

组合限制、排序和跳过

注意

更多信息

API 文档