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Django's ORM (Mapping Relational Objectum) opportunum praebet viam ut cum datorum correspondeant.

1. Django exemplum

在 `myapp/models.py` 中定义一个示例模型：

```python
from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()
    city = models.CharField(max_length=100)

    def __str__(self):
        return self.name
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Migrationem currunt imperium database mensas creare:

python manage.py makemigrations
python manage.py migrate
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2. crea

Facere unum objectum

from myapp.models import Person

# 创建并保存一个新对象
person = Person(name='Alice', age=25, city='New York')
person.save()
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usus create() methodo

person = Person.objects.create(name='Bob', age=30, city='Los Angeles')
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3. Read

Ut omnia objecta

people = Person.objects.all()
for person in people:
    print(person.name, person.age, person.city)
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Ut unum objectum

person = Person.objects.get(id=1)
print(person.name, person.age, person.city)
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Usus Filtra

# 获取所有年龄大于25的人
people = Person.objects.filter(age__gt=25)
for person in people:
    print(person.name, person.age, person.city)
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4. Update

Renovare objectum

person = Person.objects.get(id=1)
person.age = 26
person.save()
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Batch update

Person.objects.filter(city='New York').update(city='NYC')
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5. Delere

Delere unum objectum

person = Person.objects.get(id=1)
person.delete()
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batch deletionem

Person.objects.filter(age__lt=20).delete()
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6. Ordering

Sort per unum campum

people = Person.objects.all().order_by('age')
for person in people:
    print(person.name, person.age, person.city)
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Sort per plures agros

people = Person.objects.all().order_by('city', '-age')
for person in people:
    print(person.name, person.age, person.city)
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7. Grouping

Django ORM operationes copulationis directe non sustinet, sed uti potes annotate etaggregate ad consequi modi functionality similes.

usus annotate Praestare coetus numerus

from django.db.models import Count

# 按城市分组并计数
city_counts = Person.objects.values('city').annotate(count=Count('id'))
for city_count in city_counts:
    print(city_count['city'], city_count['count'])
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usus aggregate Praestare res aggregatio

from django.db.models import Avg, Max, Min

# 计算平均年龄
average_age = Person.objects.aggregate(Avg('age'))
print(average_age)  # 输出: {'age__avg': 27.5}

# 计算最大和最小年龄
age_stats = Person.objects.aggregate(Max('age'), Min('age'))
print(age_stats)  # 输出: {'age__max': 30, 'age__min': 25}
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8. Complexa queries

Q res pro universa queries

from django.db.models import Q

# 获取年龄大于25或城市为'New York'的人
people = Person.objects.filter(Q(age__gt=25) | Q(city='New York'))
for person in people:
    print(person.name, person.age, person.city)
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Comparationes inter agros F res praestare

from django.db.models import F

# 获取年龄大于等于城市长度的人
people = Person.objects.filter(age__gte=F('city__length'))
for person in people:
    print(person.name)
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