Mongoengine 简明教程
MongoEngine - Custom Query Sets
默认情况下，文档类上的 object 属性返回未应用任何筛选器的 QuerySet。但是，您可以在文档上定义类方法来修改查询集。此类方法应该接受两个参数 - doc_cls 和 queryset ，并且需要用 queryset_manager() 装饰它才能被识别。
By default, the objects attribute on a document class returns a QuerySet without applying any filter. However, you can define a classmethod on a document that modifies a queryset. Such a method should accept two arguments – doc_cls and queryset and it needs to be decorated with queryset_manager() in order for it to be recognized.
@queryset_manager
def qry_method(docs_cls,queryset):
….
----在下面的示例中，名为 products 的文档类有一个经过 @queryset_manager 装饰的 expensive_prods() 方法。该方法本身将过滤器应用于查询集，以便仅返回价格 >20000 的对象。此方法现在是默认文档查询，products 类的 objects 属性返回已筛选的文档。
In the following example, the document class called products has an expensive_prods() method which is decorated by @queryset_manager. The method itself applies a filter to queryset such that only objects with price >20000 are returned. This method is now the default document query and objects attribute of products class returns filtered documents.
from mongoengine import *
con=connect('newdb')
class products (Document):
ProductID=IntField(required=True)
company=StringField()
Name=StringField()
price=IntField()
@queryset_manager
def expensive_prods(docs_cls,queryset):
return queryset.filter(price__gt=20000)
for product in products.expensive_prods():
print ("Name:{} company:{} price:{}".format(product.Name, product.company, product.price))Output
Name:Laptop company:Acer price:25000
Name:TV company:Samsung price:50000
Name:TV company:Philips price:31000
Name:Laptop company:Dell price:45000如果您希望自定义过滤文档的方法，请首先声明 QuerySet 类的子类，并将其用作元数据中的 queryset_class 属性的值。
If you wish to customize methods for filtering documents, first declare a subclass of QuerySet class, and use it as value of queryset_class property in meta dictionary.
以下示例使用 MyQuerySet 类作为自定义查询集的定义。此类中的 myqrymethod() 过滤名称字段以“er”结尾的文档。在 products 类中，meta 属性引用此查询集子类，用作 queryset_class 属性的值。
The example below uses MyQuerySet class as definition of custom queryset. The myqrymethod() in this class filters the documents whose name field ends with ‘er’. In products class, meta attribute refers to this queryset subclass is used as value of queryset_class property.
from mongoengine import *
con=connect('newdb')
class MyQuerySet(QuerySet):
def myqrymethod(self):
return self.filter(Name__endswith='er')
class products (Document):
meta = {'queryset_class': MyQuerySet}
ProductID=IntField(required=True)
company=StringField()
Name=StringField()
price=IntField()
for product in products.objects.myqrymethod():
print ("Name:{} company:{} price:{}".format(product.Name, product.company, product.price))