Django ORM数据库操作Python化艺术探索

from django.db import models
class Author(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()
    def __str__(self):
        return self.name

python manage.py makemigrations
python manage.py migrate

new_author = Author(name='J.K. Rowling', age=54)
new_author.save()

Author.objects.create(name='George R.R. Martin', age=71)

authors = Author.objects.all()

author = Author.objects.get(name='J.K. Rowling')

young_authors = Author.objects.filter(age__lt=50)

old_authors = Author.objects.exclude(age__lt=50)

author = Author.objects.get(name='J.K. Rowling')
author.age = 55
author.save()

Author.objects.filter(age__lt=50).update(age=50)

author = Author.objects.get(name='J.K. Rowling')
author.delete()

Author.objects.filter(age__gt=70).delete()

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

books = Book.objects.filter(author__name='J.K. Rowling')

from django.db.models import Avg
average_age = Author.objects.all().aggregate(Avg('age'))

from django.db.models import Q
authors = Author.objects.filter(Q(age__gt=50) | Q(name__startswith='J'))

from django.db.models import F
authors = Author.objects.filter(age__gt=F('age') - 10)

from django.db.models import Count
books = Book.objects.annotate(num_authors=Count('author'))

# select_related用于“一对一”和“多对一”关系
books = Book.objects.select_related('author')

# prefetch_related用于“多对多”和“一对多”关系
authors = Author.objects.prefetch_related('book_set')

Author.objects.defer('age')