MongoEngine – 排序

QuerySet的 order_by() 函数用于以排序的方式获得查询结果。其用法如下 –

Qset.order_by(‘fieldname’)

默认情况下，排序顺序为升序。对于降序，在字段的名称上附加-号。例如，要获得按价格排列的升序列表 —

from mongoengine import *
con=connect('newdb')

class products (Document):
   ProductID=IntField(required=True)
   company=StringField()
   Name=StringField()
   price=IntField()
for product in products.objects.order_by('price'):
   print ("Name:{} company:{} price:{}".format(product.Name, product.company, product.price))

输出

Name:Router company:Iball price:2000
Name:Scanner company:Cannon price:5000
Name:Printer company:Cannon price:12500
Name:Laptop company:Acer price:25000
Name:TV company:Philips price:31000
Name:Laptop company:Dell price:45000
Name:TV company:Samsung price:50000

下面的代码将按名字的降序获得列表—

for product in products.objects.order_by('-Name'):
   print ("Name:{} company:{} price:{}".format(product.Name, product.company, product.price))

输出

Name:TV company:Samsung price:50000
Name:TV company:Philips price:31000
Name:Scanner company:Cannon price:5000
Name:Router company:Iball price:2000
Name:Printer company:Cannon price:12500
Name:Laptop company:Acer price:25000
Name:Laptop company:Dell price:45000

你也可以对多个字段进行排序。这段代码会让你从公司的角度，按升序排列价格表。

for product in products.objects.order_by('company','price'):
   print ("Name:{} company:{} price:{}".format(product.Name, product.company, product.price))

输出

Name:Laptop company:Acer price:25000
Name:Scanner company:Cannon price:5000
Name:Printer company:Cannon price:12500
Name:Laptop company:Dell price:45000
Name:Router company:Iball price:2000
Name:TV company:Philips price:31000
Name:TV company:Samsung price:50000