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python mongoengine使用

IT之一小佬 人气:0

一、MongoDB的安装与连接

安装：pip install mongoengine

连接mongodb数据库

from pymongo import MongoClient
cli = 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, StringField
class 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

 2.3、数据类型通用参数

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, StringField
class 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：

2.5、文档的嵌套模型

学生信息数据字典

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, ListField
class 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, \
    EmbeddedDocumentField
from 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=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=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=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：

模型中的验

模型中自定义验证方法示例代码如下：

import re
from mongoengine import StringField
from mongoengine.errors import ValidationError
def 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 random
from model import Student, Grade, SexEnum, CourseGrade
class LearnMongoDBEngine(object):
 
    def __init__(self, info):
        self.info = info
        print(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 result
if __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：

3.2、方式二：使用create()方法

User.objects.create(**kwargs)

示例代码：

import random
from model import Student, Grade, SexEnum, CourseGrade
class LearnMongoDBEngine(object):
    def __init__(self, info):
        self.info = info
        print(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 result
if __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：

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：

4.1、单个文档查询

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 Student
class 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_info
    def 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_info
    def 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_id
if __name__ == '__main__':
    obj = LearnMongoDBEngine()
    obj.get_one_student()
    obj.get_all_student()
    obj.get_student_by_id('62dcd1f1a0da9e5521e73223')

运行结果：

4.2、条件查询

1）比较运算符

 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】

3）多个条件组合查询

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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_info
    def 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_info
    def 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_id
    def 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 result
    def get_student_2(self):
        """获取所有姓李的学生"""
        result = Student.objects.filter(stu_name__startswith='李')
        print(result)
        return result
    def 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 result
    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_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 result
if __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】

4.3、聚合统计

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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_age
if __name__ == '__main__':
    obj = LearnMongoDBEngine()
    obj.get_student_4()
    obj.get_student_5()
    obj.get_man_sex()

运行结果：

 4.4、排序

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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： 

 4.5、分页处理

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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_size
        end = start + page_size
        queryset1 = 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：

 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

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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：

5.2、删除数据

User.objects.filter().delete()

from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum
class 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：

附录：

main.py 

import random
from mongoengine.queryset.visitor import Q
from model import Student, Grade, SexEnum, CourseGrade
class LearnMongoDBEngine(object):
    def __init__(self, info):
        self.info = info
        print(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 result
    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_info
    def 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_info
    def 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_id
    def 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 result
    def get_student_2(self):
        """获取所有姓李的学生"""
        result = Student.objects.filter(stu_name__startswith='李')
        print(result)
        return result
    def 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 result
    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_age
    def 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 result
    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'
    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_size
        end = start + page_size
        queryset1 = 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, \
    EmbeddedDocumentField
from 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=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=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=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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