详解python中mongoengine库用法详解python中mongoengine库用法

一、MongoDB的安装与连接
二、MongoEngine模型介绍

2.1、ODM模型介绍
2.2、常见数据类型
2.3、数据类型通用参数
2.4、类属性meta常见配置项
2.5、文档的嵌套模型

三、添加数据

3.1、方式一
3.2、方式二：使用create()方法

四、查询数据

4.1、单个文档查询
4.2、条件查询
4.3、聚合统计
4.4、排序
4.5、分页处理

五、修改和删除数据

5.1、修改数据
5.2、删除数据

【详解python中mongoengine库用法】
一、MongoDB的安装与连接安装：pip install mongoengine

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连接mongodb数据库

from pymongo import MongoClientcli = MongoClient('192.168.124.104', 27017)mongodb = cli['test']print(mongodb)

from mongoengine import connect#连接到User数据库connect('user', host='192.168.124.104', port=27017)

二、MongoEngine模型介绍
2.1、ODM模型介绍

from mongoengine import Document, StringFieldclass User(Document):email = StringField(required=True)first_name = StringField(max_length=50)last_name = StringField(max_length=50)

2.2、常见数据类型

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2.3、数据类型通用参数

db_field：文档中的field/域/列名称
required：是否为必填项
default：默认值
unique：唯一性约束
choices：可选择的列表
primary_key：是否为文档的主键，默认为False

2.4、类属性meta常见配置项
类属性，其配置项为python的dict（字典）

from mongoengine import Document, StringFieldclass User(Document):email = StringField(required=True)first_name = StringField(max_length=50)last_name = StringField(max_length=50)meta = {}

常见的配置项：

db_alias：指定文档所在的数据库（逻辑库）
collection：指定文档所在的集合
ordering：指定文档的默认排序规则
indexes：指定文档的索引规则

2.5、文档的嵌套模型
学生信息数据字典

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文档的嵌套场景
情况一，数组-简单数据类型：{'grades': [76, 51, 84]}

from mongoengine import Document, IntField, ListFieldclass Student(Document):grade = ListField(IntField())

情况二，单个文档：{'grade': {'course_name': '语文', 'score': 76}}

from mongoengine import Document, StringField, IntField, ListField, EmbeddedDocument, EmbeddedDocumentField#自定义类型class CourseGrade(EmbeddedDocument):course_name = StringField()score = IntField()class Student(Document):grade = EmbeddedDocumentField(CourseGrade)

情况三，数组-文档：{'grades': [{'score': 76}, {'score': 51}]}

from mongoengine import Document, IntField, ListField, EmbeddedDocument, EmbeddedDocumentField#自定义类型class CourseGrade(EmbeddedDocument):score = IntField()class Student(Document):grade = ListField(EmbeddedDocumentField(CourseGrade))

完整代码：

from mongoengine import Document, connect, EnumField, StringField, IntField, ListField, EmbeddedDocument, \EmbeddedDocumentFieldfrom enum import Enum#连接到User数据库connect('user', host='192.168.124.104', port=27017)class SexEnum(Enum):MAN = '男'WOMAN = '女'class CourseGrade(EmbeddedDocument):"""成绩信息（科目、老师、成绩）-被嵌套的文档"""course_name = StringField(max_length=64, required=True, verbose_name='科目')teacher = StringField(max_length=16, verbose_name='老师')score = IntField(min_value=https://www.it610.com/article/0, max_value=150, required=True, verbose_name='成绩')def __repr__(self):return f"CourseGrade({self.course_name},{self.score})"def __str__(self):return self.__repr__()class Student(Document):"""学生信息"""# verbose_name 自定义参数，用于显示定义域的名称stu_no = IntField(required=True, unique=True, verbose_name='学号')stu_name = StringField(required=True, max_length=16, verbose_name='姓名')sex = EnumField(enum=SexEnum, verbose_name='性别')class_name = StringField(max_length=10, verbose_name='班级')address = StringField(max_length=255, verbose_name='家庭住址')phone_no = StringField(max_length=11, verbose_name='电话号码')age = IntField(min_value=https://www.it610.com/article/0, max_value=150, verbose_name='年龄')grades = ListField(EmbeddedDocumentField(CourseGrade), verbose_name='成绩数组')meta = {#指定文档的集合'collection': 'students',#指定排序，可以指定多个域。例如：'age':根据年龄升序，'-age'：根据年龄降序'ordering': ['-age']}def __repr__(self):return f'Grade({self.stu_no}, {self.stu_name})'def __str__(self):return self.__repr__()class Grade(Document):"""学生成绩"""# verbose_name 自定义参数，用于显示定义域的名称stu_no = IntField(required=True, verbose_name="学号")stu_name = StringField(required=True, max_length=16, verbose_name='姓名')sex = EnumField(enum=SexEnum, verbose_name='性别')class_name = StringField(max_length=10, verbose_name='班级')address = StringField(max_length=255, verbose_name='家庭住址')phone_no = StringField(max_length=11, verbose_name='电话号码')age = IntField(min_value=https://www.it610.com/article/0, max_value=150, verbose_name='年龄')grade = EmbeddedDocumentField(CourseGrade, verbose_name='成绩')meta = {# 指定文档的集合'collection': 'grades',# 指定排序，可以指定多个域。例如：'age':根据年龄升序，'-age'：根据年龄降序'ordering': ['-age']}def __repr__(self):return f'Grade({self.stu_no}, {self.stu_name})'def __str__(self):return self.__repr__()

三、添加数据添加数据一般有两种方式：

3.1、方式一
一般步骤：

第一步，构造ODM模型类对象：user=User(username='张三')
第二步，验证数据：user.validate()
第三步，保存数据：user.save()

模型中的验

内置的验证器，如max_length, min_value
自定义验证器

模型中自定义验证方法示例代码如下：

import refrom mongoengine import StringFieldfrom mongoengine.errors import ValidationErrordef phone_required(value):pattern = r'^1[0-9][10]$'if not re.search(pattern, value):raise ValidationError('请输入正确的手机号')phone_no = StringField(validation=phone_required)

方式一示例代码：

import randomfrom model import Student, Grade, SexEnum, CourseGradeclass LearnMongoDBEngine(object): def __init__(self, info):self.info = infoprint(self.info) def add_one_student(self):"""新增一个学生信息"""student = Student(stu_no=random.randint(3000, 9999999),stu_name=self.info['name'],sex=random.choice([SexEnum.MAN, SexEnum.WOMAN]),class_name='六年级三班',address=self.info['address'],phone_no=self.info['phone'],age=random.randint(10, 15),grades=[CourseGrade(course_name='语文', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='数学', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='英语', teacher=self.info['teacher'], score=random.randint(1, 100)),])print(student, student.grades)result = student.save()return resultif __name__ == '__main__':info = {'name': '铁扇公主', 'address': '北京市朝阳区', 'phone': '19121741234', 'teacher': '王老师'} obj = LearnMongoDBEngine(info)obj.add_one_student()

mongodb数据库中插入的数据：

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3.2、方式二：使用create()方法

User.objects.create(**kwargs)

示例代码：

import randomfrom model import Student, Grade, SexEnum, CourseGradeclass LearnMongoDBEngine(object):def __init__(self, info):self.info = infoprint(self.info)def add_one_student(self):"""新增一个学生信息"""result = Student.objects.create(stu_no=random.randint(3000, 9999999),stu_name=self.info['name'],sex=random.choice([SexEnum.MAN, SexEnum.WOMAN]),class_name='六年级三班',address=self.info['address'],phone_no=self.info['phone'],age=random.randint(10, 15),grades=[CourseGrade(course_name='语文', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='数学', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='英语', teacher=self.info['teacher'], score=random.randint(1, 100)),])# student = Student(#stu_no=random.randint(3000, 9999999),#stu_name=self.info['name'],#sex=random.choice([SexEnum.MAN, SexEnum.WOMAN]),#class_name='六年级三班',#address=self.info['address'],#phone_no=self.info['phone'],#age=random.randint(10, 15),#grades=[#CourseGrade(course_name='语文', teacher=self.info['teacher'], score=random.randint(1, 100)),#CourseGrade(course_name='数学', teacher=self.info['teacher'], score=random.randint(1, 100)),#CourseGrade(course_name='英语', teacher=self.info['teacher'], score=random.randint(1, 100)),#]# )print(result, result.grades)# result = student.save()return resultif __name__ == '__main__':info = {'name': '卢俊义', 'address': '上海市浦东新区', 'phone': '18721741234', 'teacher': '张老师'}obj = LearnMongoDBEngine(info)obj.add_one_student()

mongodb数据库中插入的数据：

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四、查询数据结果集QuerySet的获取：User.objects，User是模型对象
常用的查询方法：

all()：查询所有文档
filter()：按照条件查询
count()：满足条件的文档数
sum()/average()：求和/求平均数
order_by()：排序
.skip().limit()：分页

4.1、单个文档查询

first()：没有文档则返回None，User.objects.first()
get(**kwargs)

多个文档时，异常：MultipleObjectsReturned
没有文档时，异常：DoesNotExist
仅有一个文档时：返回ODM对象
示例代码：

from model import Studentclass LearnMongoDBEngine(object):def get_one_student(self):"""查询一个学生的信息"""student_info = Student.objects.first()print(student_info, student_info.id, student_info.stu_name, student_info.address)return student_infodef get_all_student(self):"""查询所有学生的信息"""student_all_info = Student.objects.all()print(student_all_info)return student_all_infodef get_student_by_id(self, pk: str):"""根据学生的id查询"""student_info_id = Student.objects.get(id=pk)print(student_info_id)return student_info_idif __name__ == '__main__':obj = LearnMongoDBEngine()obj.get_one_student()obj.get_all_student()obj.get_student_by_id('62dcd1f1a0da9e5521e73223')

运行结果：

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4.2、条件查询
1）比较运算符

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在MongoEngine中使用双下划线(__)分割。比如：age__gt=12，表示年龄大于12的学生信息。
2）MongoEngine中的字符串查询【i表示不区分大小写】

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3）多个条件组合查询

Q函数的使用：from mongoengine.queryset.visitor import Q
多个条件同时满足：Student.objects.filter(Q(key1=value1) & Q(key2=value2))
多个条件部分满足：Student.objects.filter(Q(key1=value1) | Q(key2=value2))

from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def get_one_student(self):"""查询一个学生的信息"""student_info = Student.objects.first()print(student_info, student_info.id, student_info.stu_name, student_info.address)return student_infodef get_all_student(self):"""查询所有学生的信息"""student_all_info = Student.objects.all()print(student_all_info)return student_all_infodef get_student_by_id(self, pk: str):"""根据学生的id查询"""student_info_id = Student.objects.get(id=pk)print(student_info_id)return student_info_iddef get_student_1(self):"""获取大于12岁的学生信息"""result = Student.objects.filter(age__gt=12)print(result)return resultdef get_student_2(self):"""获取所有姓李的学生"""result = Student.objects.filter(stu_name__startswith='李')print(result)return resultdef get_student_3(self):"""查询年龄在9~12之间（含）的学生信息"""# SELECT * FROM school_student_info WHERE age BETWEEN 9 AND 12; # db.students.find({'age': {'$gte': 9, '$lte': 12}})result = Student.objects.filter(Q(age__gte=9) & Q(age__lte=12))print(result)return resultdef get_student_4(self):"""查询所有12岁以上的男生和9岁以下的女生"""result = Student.objects.filter(Q(age__gt=12, sex=SexEnum.MAN) | Q(age__lt=9, sex=SexEnum.WOMAN))print(result)return resultdef get_grade(self):"""查询大于等于60分的学生成绩信息"""result = Student.objects.filter(grades__score__gte=80)# 注意这儿写法print(result)for i in result:print(i.grades)return resultif __name__ == '__main__':obj = LearnMongoDBEngine()obj.get_one_student()obj.get_student_1()obj.get_student_2()obj.get_student_3()obj.get_student_4()obj.get_grade()

运行结果：【注意：打印信息是由model中__call__函数设置决定的】

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4.3、聚合统计

满足条件的文档数：User.objects.count()，所有的结果集都可以使用
求和/平均数：User.objects.filter().sum(field) / User.objects.filter().average(field)

from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def get_student_4(self):"""查询所有12岁以上的男生和9岁以下的女生"""result = Student.objects.filter(Q(age__gt=12, sex=SexEnum.MAN) | Q(age__lt=9, sex=SexEnum.WOMAN))print(result)return result def get_student_5(self):"""查询所有12岁以上的男生和9岁以下的女生总数"""result = Student.objects.filter(Q(age__gt=12, sex=SexEnum.MAN) | Q(age__lt=9, sex=SexEnum.WOMAN)).count()print(result)return result def get_man_sex(self):"""统计性别为男的总人数，并求出其平均年龄和总年龄"""queryset = Student.objects.filter(sex='男')print(queryset)man_num_count = queryset.count()print(man_num_count)man_avg_age = queryset.average('age')print(man_avg_age)man_sum_age = queryset.sum('age')print(man_sum_age)return man_avg_age, man_sum_ageif __name__ == '__main__':obj = LearnMongoDBEngine()obj.get_student_4()obj.get_student_5()obj.get_man_sex()

运行结果：

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4.4、排序

-：倒叙排列
(+)：正序排序，默认就是正序
Student.objects().order_by('field1', '-field2')

from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def get_max_min_age(self):"""获取最大年龄和最小年龄的学生信息"""queryset_min_age = Student.objects.order_by('age').first()queryset_max_age = Student.objects.order_by('-age').first()print(queryset_min_age, queryset_min_age.age)print(queryset_max_age, queryset_max_age.age) return '200 OK'if __name__ == '__main__':obj = LearnMongoDBEngine()obj.get_max_min_age()

运行结果：

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4.5、分页处理

方式一，切片方式：User.objects.all()[10:15]
方式二，.skip().limit()：User.objects.skip(10).limit(5)

from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def paginate(self, page: int = 1, page_size: int = 5):"""分页处理:param page: 当前是第几页:param page_size: 每页有多少数据:return:"""#方法一：切片start = (page - 1) * page_sizeend = start + page_sizequeryset1 = Student.objects.all()[start:end]print(queryset1)#方法二：skip().limit()queryset2 = Student.objects.skip(start).limit(page_size)print(queryset2)return "200 OK"if __name__ == '__main__':obj = LearnMongoDBEngine()obj.paginate(1, 6)print("*" * 100)obj.paginate(1, 3)obj.paginate(2, 3)

运行结果：

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五、修改和删除数据
5.1、修改数据
修改数据时一般先过滤数据，再修改

修改一条数据：User.objects.filter().update_one()
批量修改数据：User.objects.filter().update()

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from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def update_one(self):"""修改一条数据"""queryset = Student.objects.filter(stu_no='2438197')print(queryset)result = queryset.update_one(stu_name='白龙马', phone_no='16452412564')# result = queryset.update_one(stu_name='白龙马', unset__phone_no=True)print(result)def update_one_2(self):"""修改一条数据"""queryset = Student.objects.filter(stu_no=3152784).first()print(queryset)if queryset:queryset.stu_name = '沙和尚'result = queryset.save()print(result)return "200 OK"else:return "error"def update_many(self):"""将年龄10岁的学生年龄加一岁"""queryset = Student.objects.filter(age=10)print(queryset)queryset.update(inc__age=1)print(queryset)return "200 OK"if __name__ == '__main__':obj = LearnMongoDBEngine()obj.update_one()obj.update_one_2()obj.update_many()

运行结果：

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5.2、删除数据
User.objects.filter().delete()

from mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnumclass LearnMongoDBEngine(object):def delete_data(self):"""删除年龄大于13岁的学生"""queryset_start = Student.objects.all()print(f"删除前学生总数量：{queryset_start.count()}")queryset = Student.objects.filter(age__gt=13)print(f'删除的学生的数量：{queryset.count()}')res = queryset.delete()print(f"删除的结果：{res}")queryset_end = Student.objects.all()print(f"删除后剩余学生总数量：{queryset_end.count()}")if __name__ == '__main__':obj = LearnMongoDBEngine()obj.delete_data()

运行结果：

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附录：
main.py

import randomfrom mongoengine.queryset.visitor import Qfrom model import Student, Grade, SexEnum, CourseGradeclass LearnMongoDBEngine(object):def __init__(self, info):self.info = infoprint(self.info)def add_one_student(self):"""新增一个学生信息"""result = Student.objects.create(stu_no=random.randint(3000, 9999999),stu_name=self.info['name'],sex=random.choice([SexEnum.MAN, SexEnum.WOMAN]),class_name='六年级三班',address=self.info['address'],phone_no=self.info['phone'],age=random.randint(10, 15),grades=[CourseGrade(course_name='语文', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='数学', teacher=self.info['teacher'], score=random.randint(1, 100)),CourseGrade(course_name='英语', teacher=self.info['teacher'], score=random.randint(1, 100)),])# student = Student(#stu_no=random.randint(3000, 9999999),#stu_name=self.info['name'],#sex=random.choice([SexEnum.MAN, SexEnum.WOMAN]),#class_name='六年级三班',#address=self.info['address'],#phone_no=self.info['phone'],#age=random.randint(10, 15),#grades=[#CourseGrade(course_name='语文', teacher=self.info['teacher'], score=random.randint(1, 100)),#CourseGrade(course_name='数学', teacher=self.info['teacher'], score=random.randint(1, 100)),#CourseGrade(course_name='英语', teacher=self.info['teacher'], score=random.randint(1, 100)),#]# )print(result, result.grades)# result = student.save()return resultdef get_one_student(self):"""查询一个学生的信息"""student_info = Student.objects.first()print(student_info, student_info.id, student_info.stu_name, student_info.address)return student_infodef get_all_student(self):"""查询所有学生的信息"""student_all_info = Student.objects.all()print(student_all_info)return student_all_infodef get_student_by_id(self, pk: str):"""根据学生的id查询"""student_info_id = Student.objects.get(id=pk)print(student_info_id)return student_info_iddef get_student_1(self):"""获取大于12岁的学生信息"""result = Student.objects.filter(age__gt=12)print(result)return resultdef get_student_2(self):"""获取所有姓李的学生"""result = Student.objects.filter(stu_name__startswith='李')print(result)return resultdef get_student_3(self):"""查询年龄在9~12之间（含）的学生信息"""# SELECT * FROM school_student_info WHERE age BETWEEN 9 AND 12; # db.students.find({'age': {'$gte': 9, '$lte': 12}})result = Student.objects.filter(Q(age__gte=9) & Q(age__lte=12))print(result)return resultdef get_student_4(self):"""查询所有12岁以上的男生和9岁以下的女生"""result = Student.objects.filter(Q(age__gt=12, sex=SexEnum.MAN) | Q(age__lt=9, sex=SexEnum.WOMAN))print(result)return resultdef get_student_5(self):"""查询所有12岁以上的男生和9岁以下的女生总数"""result = Student.objects.filter(Q(age__gt=12, sex=SexEnum.MAN) | Q(age__lt=9, sex=SexEnum.WOMAN)).count()print(result)return resultdef get_man_sex(self):"""统计性别为男的总人数，并求出其平均年龄和总年龄"""queryset = Student.objects.filter(sex='男')print(queryset)man_num_count = queryset.count()print(man_num_count)man_avg_age = queryset.average('age')print(man_avg_age)man_sum_age = queryset.sum('age')print(man_sum_age)return man_avg_age, man_sum_agedef get_grade(self):"""查询大于等于60分的学生成绩信息"""result = Student.objects.filter(grades__score__gte=80)# 注意这儿写法print(result)for i in result:print(i.grades)return resultdef get_max_min_age(self):"""获取最大年龄和最小年龄的学生信息"""queryset_min_age = Student.objects.order_by('age').first()queryset_max_age = Student.objects.order_by('-age').first()print(queryset_min_age, queryset_min_age.age)print(queryset_max_age, queryset_max_age.age)return '200 OK'def paginate(self, page: int = 1, page_size: int = 5):"""分页处理:param page: 当前是第几页:param page_size: 每页有多少数据:return:"""#方法一：切片start = (page - 1) * page_sizeend = start + page_sizequeryset1 = Student.objects.all()[start:end]print(queryset1)#方法二：skip().limit()queryset2 = Student.objects.skip(start).limit(page_size)print(queryset2)return "200 OK"def update_one(self):"""修改一条数据"""queryset = Student.objects.filter(stu_no='2438197')print(queryset)result = queryset.update_one(stu_name='白龙马', phone_no='16452412564')# result = queryset.update_one(stu_name='白龙马', unset__phone_no=True)print(result)def update_one_2(self):"""修改一条数据"""queryset = Student.objects.filter(stu_no=3152784).first()print(queryset)if queryset:queryset.stu_name = '沙和尚'result = queryset.save()print(result)return "200 OK"else:return "error"def update_many(self):"""将年龄10岁的学生年龄加一岁"""queryset = Student.objects.filter(age=10)print(queryset)queryset.update(inc__age=1)print(queryset)return "200 OK"def delete_data(self):"""删除年龄大于13岁的学生"""queryset_start = Student.objects.all()print(f"删除前学生总数量：{queryset_start.count()}")queryset = Student.objects.filter(age__gt=13)print(f'删除的学生的数量：{queryset.count()}')res = queryset.delete()print(f"删除的结果：{res}")queryset_end = Student.objects.all()print(f"删除后剩余学生总数量：{queryset_end.count()}")if __name__ == '__main__':#自我测试代码pass

model.py

from mongoengine import Document, connect, EnumField, StringField, IntField, ListField, EmbeddedDocument, \EmbeddedDocumentFieldfrom enum import Enum#连接到User数据库connect('user', host='192.168.124.104', port=27017)class SexEnum(Enum):MAN = '男'WOMAN = '女'class CourseGrade(EmbeddedDocument):"""成绩信息（科目、老师、成绩）-被嵌套的文档"""course_name = StringField(max_length=64, required=True, verbose_name='科目')teacher = StringField(max_length=16, verbose_name='老师')score = IntField(min_value=https://www.it610.com/article/0, max_value=150, required=True, verbose_name='成绩')def __repr__(self):return f"CourseGrade({self.course_name},{self.score})"def __str__(self):return self.__repr__()class Student(Document):"""学生信息"""# verbose_name 自定义参数，用于显示定义域的名称stu_no = IntField(required=True, unique=True, verbose_name='学号')stu_name = StringField(required=True, max_length=16, verbose_name='姓名')sex = EnumField(enum=SexEnum, verbose_name='性别')class_name = StringField(max_length=10, verbose_name='班级')address = StringField(max_length=255, verbose_name='家庭住址')phone_no = StringField(max_length=11, verbose_name='电话号码')age = IntField(min_value=https://www.it610.com/article/0, max_value=150, verbose_name='年龄')grades = ListField(EmbeddedDocumentField(CourseGrade), verbose_name='成绩数组')meta = {#指定文档的集合'collection': 'students',#指定排序，可以指定多个域。例如：'age':根据年龄升序，'-age'：根据年龄降序'ordering': ['-age'],'strict': False# 设置非严格校验字段则不需要吧所有字段都声明}def __repr__(self):return f'Grade({self.stu_no}, {self.stu_name})'def __str__(self):return self.__repr__()class Grade(Document):"""学生成绩"""# verbose_name 自定义参数，用于显示定义域的名称stu_no = IntField(required=True, verbose_name="学号")stu_name = StringField(required=True, max_length=16, verbose_name='姓名')sex = EnumField(enum=SexEnum, verbose_name='性别')class_name = StringField(max_length=10, verbose_name='班级')address = StringField(max_length=255, verbose_name='家庭住址')phone_no = StringField(max_length=11, verbose_name='电话号码')age = IntField(min_value=https://www.it610.com/article/0, max_value=150, verbose_name='年龄')grades = EmbeddedDocumentField(CourseGrade, verbose_name='成绩')meta = {# 指定文档的集合'collection': 'grades',# 指定排序，可以指定多个域。例如：'age':根据年龄升序，'-age'：根据年龄降序'ordering': ['-age']}def __repr__(self):return f'Grade({self.stu_no}, {self.stu_name})'def __str__(self):return self.__repr__()

官方文档：
https://docs.mongoengine.org/guide/querying.html
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