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Django点滴(5)-建模

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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=Falseauto_now_add=False**options])
DateTimeField([auto_now=Falseauto_now_add=False**options])
DecimalField(max_digits=Nonedecimal_places=None[**options])
EmailField([max_length=75**options])
FileField(upload_to=None[max_length=100**options])
FloatField([**options])
ImageField(upload_to=None[height_field=Nonewidth_field=Nonemax_length=100**options])
IntegerField([**options])
IPAddressField([**options])
TextField([**options])
TimeField([auto_now=Falseauto_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]

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