Django项目优化数据库操作总结

class ModelName(models.Model):
	# 字段添加索引使用db_index
	name = models.CharField(db_index=True, max_length=100)
	class Meta:
		# 联合唯一索引使用index_together
		index_together = ('字段1', '字段2')

# 标准查询
# Hits the database.
e = Entry.objects.get(id=5)
# Hits the database again to get the related Blog object.
b = e.blog
# select_related 查询
# Hits the database.
e = Entry.objects.select_related('blog').get(id=5)
# Doesn't hit the database, because e.blog has been prepopulated
# in the previous query.
b = e.blog

from django.db import models
class Topping(models.Model):
    name = models.CharField(max_length=30)
class Pizza(models.Model):
    name = models.CharField(max_length=50)
    toppings = models.ManyToManyField(Topping)
    def __str__(self):
        return "%s (%s)" % (
            self.name,
            ", ".join(topping.name for topping in self.toppings.all()),
        )
# Good
pizza.objects.all().prefetch_related('toppings')

# Good
Entry.objects.bulk_create([
    Entry(headline='This is a test'),
    Entry(headline='This is only a test'),
])
# Bad
Entry.objects.create(headline='This is a test')
Entry.objects.create(headline='This is only a test')

# Good
entries[0].headline = 'This is not a test'
entries[1].headline = 'This is no longer a test'
Entry.objects.bulk_update(entries, ['headline'])
# Bad
entries[0].headline = 'This is not a test'
entries[0].save()
entries[1].headline = 'This is no longer a test'
entries[1].save()

# Good
my_band.members.add(me, my_friend)
# Bad
my_band.members.add(me)
my_band.members.add(my_friend)
# Good
PizzaToppingRelationship = Pizza.toppings.through
PizzaToppingRelationship.objects.bulk_create([
    PizzaToppingRelationship(pizza=my_pizza, topping=pepperoni),
    PizzaToppingRelationship(pizza=your_pizza, topping=pepperoni),
    PizzaToppingRelationship(pizza=your_pizza, topping=mushroom),
], ignore_conflicts=True)
# Bad
my_pizza.toppings.add(pepperoni)
your_pizza.toppings.add(pepperoni, mushroom)

# Good
my_band.members.remove(me, my_friend)
# Bad
my_band.members.remove(me)
my_band.members.remove(my_friend)
# Good
from django.db.models import Q
PizzaToppingRelationship = Pizza.toppings.through
PizzaToppingRelationship.objects.filter(
    Q(pizza=my_pizza, topping=pepperoni) |
    Q(pizza=your_pizza, topping=pepperoni) |
    Q(pizza=your_pizza, topping=mushroom)
).delete()
# Bad
my_pizza.toppings.remove(pepperoni)
your_pizza.toppings.remove(pepperoni, mushroom)