如何在Python中使一组组合字段在Mongodb中唯一

Question

我想创建一个表，其中两个字段组合在一起形成一个索引字段。创建表的Python代码如下。我要做的是使组合字段course_name和group_name唯一，这样就不会创建具有相同course_name和{}的两个组。有人能帮我吗？在

class SocialGroup(Document):
    timestamp = DateTimeField(default=datetime.now)
    course_name = StringField()
    group_name = StringField(choices=[('A', 1), ('B', 1), ('C', 1),('D', 1), ('E', 1), ('F', 1), ('None',1)], default="None")

Answer 1

发件人：http://docs.mongoengine.org/guide/defining-documents.html#uniqueness-constraints

You may also specify multi-field uniqueness constraints by using unique_with, which may be either a single field name, or a list or tuple of field names

在您的情况下：

class SocialGroup(Document):
    timestamp = DateTimeField(default=datetime.now)
    course_name = StringField()
    group_name = StringField(choices=[('A', 1), ('B', 1), ('C', 1),('D', 1), ('E', 1), ('F', 1), ('None',1)], default="None",
                             unique_with='course_name')

或者更复杂：

^{pr2}$

Answer 2

您可以在类的metadict中指定indexes：

class SocialGroup(Document):
    timestamp = DateTimeField(default=datetime.now)
    course_name = StringField()
    group_name = StringField(choices=[('A', 1), ('B', 1), ('C', 1),('D', 1), ('E', 1), ('F', 1), ('None',1)], default="None")
    meta = {
        'indexes': [
            {'fields': ('course_name', 'group_name'), 'unique': True}
        ]
    }