Django点滴（五）建模

ORM为数据库建模带来了便利。

https://docs.djangoproject.com/en/dev/topics/db/models/

https://docs.djangoproject.com/en/dev/ref/models/fields/#model-field-types

例如下列定义会自动生成SQL语句：

from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)

CREATE TABLE myapp_person (
    "id" serial NOT NULL PRIMARY KEY,
    "first_name" varchar(30) NOT NULL,
    "last_name" varchar(30) NOT NULL
);

常见字段域

AutoField ( **options )

BigIntegerField([**options])

BooleanField(**options)

CharField(max_length=None[, **options])

CommaSeparatedIntegerField(max_length=None[, **options])

DateField ( [ auto_now=False ,  auto_now_add=False ,  **options ] )

DateTimeField([auto_now=False, auto_now_add=False, **op tions ] )

DecimalField(max_digits=None, decimal_places=None[, **options])

EmailField([max_length=75, **options])

FileField(upload_to=None[, max_length=100, **options])

FloatField([**options])

ImageField(upload_to=None[, height_field=None, width_field=None, max_length=100, **options])

IntegerField([**options])

IPAddressField([**options])

TextField([**options])

TimeField([auto_now=False, auto_now_add=False, **options])

URLField([max_length=200, **options])

字段域的参数(options)

null 是否可以为null

blank 是否可以为空

default 缺省值

choices 枚举类型

class Student(models.Model):
    FRESHMAN = 'FR'
    SOPHOMORE = 'SO'
    JUNIOR = 'JR'
    SENIOR = 'SR'
    YEAR_IN_SCHOOL_CHOICES = (
        (FRESHMAN, 'Freshman'),
        (SOPHOMORE, 'Sophomore'),
        (JUNIOR, 'Junior'),
        (SENIOR, 'Senior'),
    )
    year_in_school = models.CharField(max_length=2,
                                      choices=YEAR_IN_SCHOOL_CHOICES,
                                      default=FRESHMAN)

    def is_upperclass(self):
        return self.year_in_school in (self.JUNIOR, self.SENIOR)

primary_key 是否为主键。如果不指定主键，会自动生成id字段作为主键。

unique 是否唯一

unique_for_date 是否对日期唯一

validator 指定验证器

verbose_name 更友好的显示名称（注意，django/admin 用到的是覆盖后的model.Model.__unicode__()方法）

关系字段域

外键：

class Car(models.Model):
    manufacturer = models.ForeignKey('Manufacturer')
    # ...

class Manufacturer(models.Model):
    # ...

多对多：

class Topping(models.Model):
    # ...

class Pizza(models.Model):
    # ...
    toppings = models.ManyToManyField(Topping)

多对多间接关系（注意 Person和Group不是直接关联的，而是通过 through='Membership'）：

class Person(models.Model):
    name = models.CharField(max_length=128)

    def __unicode__(self):
        return self.name

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(Person, through='Membership')

    def __unicode__(self):
        return self.name

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=64)

>>> ringo = Person.objects.create(name="Ringo Starr")
>>> paul = Person.objects.create(name="Paul McCartney")
>>> beatles = Group.objects.create(name="The Beatles")
>>> m1 = Membership(person=ringo, group=beatles,
...     date_joined=date(1962, 8, 16),
...     invite_reason= "Needed a new drummer.")
>>> m1.save()
>>> beatles.members.all()
[<Person: Ringo Starr>]
>>> ringo.group_set.all()
[<Group: The Beatles>]
>>> m2 = Membership.objects.create(person=paul, group=beatles,
...     date_joined=date(1960, 8, 1),
...     invite_reason= "Wanted to form a band.")
>>> beatles.members.all()
[<Person: Ringo Starr>, <Person: Paul McCartney>]

# THIS WILL NOT WORK
>>> beatles.members.add(john)
# NEITHER WILL THIS
>>> beatles.members.create(name="George Harrison")
# AND NEITHER WILL THIS
>>> beatles.members = [john, paul, ringo, george]