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 modelsclass 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, **options])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nullblank 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.nameclass Group(models.Model):    name = models.CharField(max_length=128)    members = models.ManyToManyField(Person, through='Membership')    def __unicode__(self):        return self.nameclass 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]