django model的一些用法

時間 2019-11-10

原文原文鏈接

Django中級用法

抽象models類

class BaseProfile(models.Model):
    USER_TYPES = (
        (0, 'Ordinary'),
        (1, 'SuperHero'),
    )

    user = models.OnToOneField(settings.AUTH_USER_MODEL, primary_key=True)
    user_type = models.IntegerField(max_length=1, null=True,    choices=USER_TYPES)
    bio = models.CharField(max_length=200, blank=True, null=True)

    def __str__(self):
        return "{}:{:.20}".format(self.user, self.bio or "")

    class Meta:
        abstract = True


class SuperHeroProfile(models.Model):
    origin = models.CharField(max_length=100, blank=True, null=True)

    class Meta:
        abstract = True


class OrdinaryProfile(models.Model):
    address = models.CharField(max_length=200, blank=True, null=True)

    class Meta:
        abstract = True


class Profile(SuperHeroProfile, OrdinaryProfile, BaseProfile):
    pass

擴展django內建User

定義(Profile.models)html

# models.py
# 將primary_key賦值爲True，以阻止相似PostgreSQL這樣的數據庫後端中的併發問題
class Profile(models.Model):
    user = models.OnToOneField(settings.AUTH_USER_MODEL, primary_key=True)

信號

# signals.py
from django.db.models.signals import post_save
from django.dispatch import receiver
from django.conf import settings
from . import models


@receiver(post_save, sender=settings.AUTH_USER_MODEL)
def create_profile_handler(sender, instance, created, **kwargs):
    if not created:
        return
    # 僅在created是最新時才建立帳戶對象
    profile = models.Profile(user=instance)
    profile.save()

首先，爲你的應用建立一個__init__.py包以引用應用的ProfileConfig:python

# __init__.py
default_app_config = "profile.apps.ProfileConfig"

接下來是app.py中的子類ProfileConfig方法，可以使用ready方法配置信號：web

# apps.py
from django.apps import AppConfig

class ProfileConfig(AppConfig):
    name = "profiles"
    verbose_name = "User Profiles"

    def ready(self):
        from . import signals

爲了操做方便，帳戶admin能夠經過定義一個自定義的UserAdmin嵌入到默認的用戶admin中：數據庫

# admin.py
from django.contrib import admin
from .models import Profile
from django.contrib.auth.models import User


class UserProfileInline(admin.StackedInline):
    model = Profile


class UserAdmin(admin.UserAdmin):
    inlines = [UserProfileInline]


admin.site.unregister(User)
admin.site.register(User, UserAdmin)

更新：django

上下文Mixin

class FeedMixin(object):
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["feed"] = models.Post.objects.viewable_posts(self.request.user)
        return context

注意雙星號包含的變量

class MyFeed(**FeedMixin**, generic.CreateView):
    model = models.Post
    template_name = "myfeed.html"
    success_url = reverse_lazy("my_feed")

服務模式

# service.py
API_URL = "http://api.herocheck.com/?q={0}"

class SuperHeroWebAPI:
    ...

    @staticmehtod
    def is_hero(username):
        url = API_URL.format(username)
        return webclient.get(url)

加上黑名單功能的服務

class SuperHeroWebAPI:
    ...

    @staticmethod
    def is_hero(username):
        blacklist = set(["syndrome", "kcka$$", "superfake"])
        ulr = API_URL.format(username)
        return username not in blacklist and webclient.get(url)

使用服務後端

from .services import SuperHeroWebAPI

def is_superhero(self):
    return SuperHeroWebAPI.is_superhero(self.user.username)

模型的方法做爲屬性

Python類可使用property裝飾器把函數看成一個屬性來使用。這樣，Django模型也能夠較好地利用它。替換前面那個例子中的函數：api

@property
def age(self):
    ...

如今咱們能夠用profile.age來訪問用戶的年齡。注意，函數的名稱要儘量的短。

緩存特性

很好理解，直接看代碼：緩存

from django.utils.function import cached_property
    #...
    @cached_property
    def full_name(self):
        # 代價高昂的操做，好比，外部服務調用
        return "{0} {1}".format(self.firstname, self.lastname)

定製模型管理器(Manager)

太簡單了，直接看官網併發

Querysets 組合查詢

from django.db.models import Q

# Union 交集
>>> User.objects.filter(Q(username__in["a", "b", "c"]) | Q(username__in=["c", "d"]))
[`<User: a>, <User: b>, <User: c>, <User: d>`]

# Intersection 並集
>>> User.objects.filter(Q(username__in["a", "b", "c"]) & Q(username__in=["c", "d"]))
[<User: c>]

# Difference 補集
>>> User.objects.filter(Q(username__in=["a", "b", "c"]) & ~Q(username__in=["c", "d"]))
[<User: a>, <User: b>]

Querysets連接

這是一個很天真的作法，開銷很大：app

>>> recent = list(posts)+list(comments)
>>> sorted(recent, key=lambda e: e.modified, reverse=True)[:3]
[<Post: user: Post1>, <Comment: user: Comment1>, <Post: user: Post0>]

一個更好的解決方案是使用迭代器減小內存消耗。以下，使用itertools.chain方法合併多個QuerySets：

>>> from itertools import chain
>>> recent = chain(posts, comments)
>>> sorted(recent, key=lambda e: e.modified, reverse=True)[:3]

以上：2016年05月31日14:51:32

裝飾器

第一種

@login_required
def simple_view(request):
       return HttpResponse()

2 經過對基於函數視圖或者基於類視圖使用一個裝飾器實現控制：

@login_required(MyView.as_view())

3 經過覆蓋mixin的類視圖的dispatch方法實現控制：

class LoginRequiredMixin:
    @method_decorator(login_required)
    def dispatch(self, request, *args, **kwargs):
        return super().dispatch(request, *args, **kwargs)

nav active的問題

每一個模板都要包含下列代碼：

{% include "_navbar.html" with active_link='link2' %}

而後

{# _navbar.html #}
<ul class="nav nav-pills">
  <li{% if active_link == "link1" %} class="active"{% endif %}><a
href="{% url 'link1' %}">Link 1</a></li>
  <li{% if active_link == "link2" %} class="active"{% endif %}><a
href="{% url 'link2' %}">Link 2</a></li>
  <li{% if active_link == "link3" %} class="active"{% endif %}><a
href="{% url 'link3' %}">Link 3</a></li>
</ul>

以前我都是從view傳一個current_page變量來判斷的，好蠢

Template tag

# app/templatetags/nav.py
from django.core.urlresolvers import resolve
from django.template import Library

register = Library()

@register.simple_tag
def active_nav(request, url):
   url_name = resolve(request.path).url_name
   if url_name == url:
       return "active"
   return ""

使用：

{# base.html #}
{% load nav %}
<ul class="nav nav-pills">
  <li class={% active_nav request 'active1' %}><a href="{% url
'active1' %}">Active 1</a></li>
  <li class={% active_nav request 'active2' %}><a href="{% url
'active2' %}">Active 2</a></li>
  <li class={% active_nav request 'active3' %}><a href="{% url
'active3' %}">Active 3</a></li>
</ul>

動態表單

# forms.py
class PersonDetailsForm(forms.Form):
    name = forms.CharField(max_length=100)
    age = forms.IntegerField()
    def __init__(self, *args, **kwargs):
       upgrade = kwargs.pop("upgrade", False)
       super().__init__(*args, **kwargs)
       # Show first class option? 顯示頭等艙選項？
       if upgrade:
            self.fields["first_class"] = forms.BooleanField(label="Fly First Class?")

# views.py
class PersonDetailsEdit(generic.FormView):
    ...
    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        kwargs["upgrade"] = True
        return kwargs

用戶表單(表單須要根據已經登陸的用戶來進行定製)

須要django-braces庫

from braces.forms import UserKwargModelFormMixin

class PersonDetailsForm(UserKwargModelFormMixin, forms.Form):
    ...
    def __init__(self, *args, **kwargs):
       super().__init__(*args, **kwargs)
       # Are you a member of the VIP group?
       if self.user.groups.filter(name="VIP").exists():
           self.fields["first_class"] = forms.BooleanField(label="Fly First Class?")

而後再確認只有登陸用戶才能看到此視圖

class VIPCheckFormView(LoginRequiredMixin, UserFormKwargsMixin,
generic.FormView):
   form_class = PersonDetailsForm
   ...

一個視圖的多個表單行爲

crispy表單訂閱器修改不一樣的按鈕

# forms.py
class SubscribeForm(forms.Form):
    email = forms.EmailField()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.helper = FormHelper(self)
        self.helper.layout.append(Submit('subscribe_butn', 'Subscribe'))

UnSubscribeForm以徹底相同的方式來定義，除了按鈕不一樣

# views.py
from .forms import SubscribeForm, UnSubscribeForm

class NewsletterView(generic.TemplateView):
   subcribe_form_class = SubscribeForm
   unsubcribe_form_class = UnSubscribeForm
   template_name = "newsletter.html"

   def get(self, request, *args, **kwargs):
       kwargs.setdefault("subscribe_form", self.subcribe_form_class())
       kwargs.setdefault("unsubscribe_form", self.unsubcribe_form_class())
       return super().get(request, *args, **kwargs)

單獨來看post方法

def post(self, request, *args, **kwargs):
       form_args = {
           'data': self.request.POST,
           'files': self.request.FILES,
       }

       if "subscribe_butn" in request.POST:
           form = self.subcribe_form_class(**form_args)
           if not form.is_valid():
               return self.get(request,
                                  subscribe_form=form)
           return redirect("success_form1")
       elif "unsubscribe_butn" in request.POST:
           form = self.unsubcribe_form_class(**form_args)
           if not form.is_valid():
               return self.get(request,
                                  unsubscribe_form=form)
           return redirect("success_form2")
       return super().get(request)

這裏我感受登陸和註冊兩個表單能夠用這個方法