更新: 刚发现在选择特定相册时 ManyToManyField 导致管理界面崩溃。我将它们注释掉，注释掉对它的所有引用，重新运行 makemigrations 和 migrate，现在管理界面再次工作......这让我离制作这个更远了“最喜欢的”专栏作品 :( 请参阅此跟进:Why is Django ManyToManyField causing admin interface to crash? Why is no through table being created?
背景:我的目标是成为“最爱？”此网页中的列反射(reflect)了当前登录用户最喜欢的相册，其中每个是“否”或"is"，并且是一个可单击的链接以切换选择。 (未登录时，它们都是灰色的“n/a”-s。)
因此，对于每个相册，每个用户可能恰好有零个或一个“已收藏”条目。如果该条目存在，则表示他们收藏了它。如果它不存在，他们就没有。
这是我的 Album 模型，带有 favorited_by_users 多对多列(完整的 models.py 在底部):
class Album(models.Model):
OFFICIALITY = (
('J', 'Major studio release'),
('I', 'Non-major official release'),
('U', 'Unofficial'),
)
title = models.CharField(max_length=70)
description = models.TextField(max_length=500, default="", null=True, blank=True)
pub_date = models.DateField('release date')
officiality = models.CharField(max_length=1, choices=OFFICIALITY)
is_concert = models.BooleanField(default=False)
main_info_url = models.URLField(blank=False)
thumbnail = models.FileField(upload_to=get_upload_file_name, blank=True, null=True)
#virtual field to skip over the through table.
songs = models.ManyToManyField("Song", through="AlbumSong")
favorited_by_users = models.ManyToManyField(User)
def __str__(self):
return self.title
class Meta:
#Default ordering is by release date, ascending.
ordering = ['pub_date']
我最初有这个 FavoriteAlbum 模型，但是由于它除了外键之外没有额外的信息，所以建议我删除它以支持上面的多对多列。
class FavoriteSongs(models.Model):
user = models.ForeignKey(User)
song = models.ForeignKey(Song)
class Meta:
unique_together = ('user', 'song',)
def __str__(self):
return "user=" + str(self.user) + ", song=" + str(self.song)
我需要做的是相册和用户之间的“左连接”，其中所有相册都被选中，并且当前登录用户的任何收藏夹都加入其中(None 如果他们还没有收藏它)。我不知道该怎么办。
我也听说过 extra()函数来执行此连接。 View 的 get_queryset() 中的当前工作查询是
return super(AlbumList, self).get_queryset().order_by("pub_date")
(下面是完整的 views.py。)我目前的猜测是:
return super(AlbumList, self).get_queryset().order_by("pub_date").extra(select={"is_favorite": "favorited_by_users__id = "+ str(request.user.id) })
但是，虽然这不会崩溃，但模板中每个 {{ is_favorite }} 的值都是nothing(空字符串)。这是有道理的，因为数据库中还没有任何内容，但是现在呢？我不知道这是否是正确的 Django 查询。
我想在数据库中添加一个项目来测试它，在 postgres 中使用手动 SQL 语句(还不是通过 Django 命令)，但是我应该如何以及在何处执行此操作？
我已成功运行 makemigrations，然后使用这个新的 m2m 列(并且没有 FavoriteSongs 模型)进行 migrate，但我什么也没看到在代表 is-favorite 值的数据库中。 billyjoel_album 中没有额外的列，也没有类似于 billyjoel_favoritealbum 的直通表。那么这些数据在数据库中存储在哪里/如何存储？
(关于这个额外的“收藏夹”列的任何其他建议也将不胜感激!)
谢谢。
模型.py
from django.db import models
from django.contrib.auth.models import User
from time import time
def get_upload_file_name(instance, filename):
return "uploaded_files/%s_%s" % (str(time()).replace(".", "_"), filename)
class Album(models.Model):
OFFICIALITY = (
('J', 'Major studio release'),
('I', 'Non-major official release'),
('U', 'Unofficial'),
)
title = models.CharField(max_length=70)
description = models.TextField(max_length=500, default="", null=True, blank=True)
pub_date = models.DateField('release date')
officiality = models.CharField(max_length=1, choices=OFFICIALITY)
is_concert = models.BooleanField(default=False)
main_info_url = models.URLField(blank=False)
thumbnail = models.FileField(upload_to=get_upload_file_name, blank=True, null=True)
#virtual field to skip over the through table.
songs = models.ManyToManyField("Song", through="AlbumSong")
favorited_by_users = models.ManyToManyField(User)
def __str__(self):
return self.title
class Meta:
#Default ordering is by release date, ascending.
ordering = ['pub_date']
class Song(models.Model):
name = models.CharField(max_length=100)
description = models.TextField(max_length=500, default="", null=True, blank=True)
length_seconds = models.IntegerField()
lyrics_url = models.URLField(default="", blank=True, null=True)
albums = models.ManyToManyField("Album", through="AlbumSong")
favorited_by_users = models.ManyToManyField(User)
def get_length_desc_from_seconds(self):
if(self.length_seconds == -1):
return "-1"
m, s = divmod(self.length_seconds, 60)
h, m = divmod(m, 60)
if(h):
return "%d:%02d:%02d" % (h, m, s)
else:
return "%d:%02d" % (m, s)
def __str__(self):
return self.name
class AlbumSong(models.Model):
song = models.ForeignKey(Song)
album = models.ForeignKey(Album)
sequence_num = models.IntegerField()
class Meta:
unique_together = ('album', 'sequence_num',)
unique_together = ('album', 'song',)
def __str__(self):
return str(self.album) + ": " + str(self.sequence_num) + ": " + str(self.song)
View .py
from .models import Album, Song, AlbumSong
from datetime import datetime, timedelta
from django.core.context_processors import csrf
from django.shortcuts import render, render_to_response
from django.views.generic import DetailView, ListView
from enum import Enum
def get_str_with_appended(string, between_if_str_non_empty, new_value):
if(len(string) == 0):
return new_value
else:
return string + between_if_str_non_empty + new_value
class PrependQuestionMark(Enum):
YES, NO = range(2)
def get_url_param_string_from_params(prepend_question_mark=PrependQuestionMark.YES, **kwargs_all_params):
param_list = ""
for key in iter(kwargs_all_params):
value = kwargs_all_params[key]
if(value is not None):
param_list = get_str_with_appended(param_list, '&', str(key) + "=" + str(value))
if(len(param_list) == 0):
return param_list;
if(prepend_question_mark == PrependQuestionMark.YES):
return "?" + param_list
else:
return param_list
class AlbumList(ListView):
model = Album
context_object_name = "albums"
#Derived from irc/#dango/tbaxter...START
def dispatch(self, request, *args, **kwargs):
#default to asc
self.sort_order = request.GET.get("sort_order", None)
self.sort_item = request.GET.get("sort_item", None)
self.csrf_token = csrf(request)["csrf_token"]
self.logged_in_user = request.user
#self.csrf_token = request.GET.get("csrf_token", None)
return super(AlbumList, self).dispatch(request, *args, **kwargs)
def get_queryset(self):
#Item zero in both is the default
#should be static global
asc_desc_list = ["asc", "dsc"]
sort_by_types = ["pub_date", "title"]
if(self.sort_order is None and self.sort_item is None):
#Use default ordering
return super(AlbumList, self).get_queryset()
#Custom ordering requested
sort_order = self.sort_order
sort_item = self.sort_item
if(sort_order is None or
sort_order not in asc_desc_list):
sort_order = asc_desc_list[0]
if(sort_item is None or
sort_item not in sort_by_types):
sort_item = sort_by_types[0]
order_minus = "" if sort_order == "asc" else "-"
return super(AlbumList, self).get_queryset().order_by(order_minus + sort_item).extra(select={"is_favorite": "favorited_by_users__id = " + str(self.logged_in_user.id) })
def get_context_data(self, **kwargs):
context = super(AlbumList, self).get_context_data(**kwargs)
context["sort_order"] = self.sort_order
context["sort_item"] = self.sort_item
context["url_params"] = get_url_param_string_from_params(
sort_item=self.sort_item,
sort_order=self.sort_order,
csrf_token=self.csrf_token)
return context
class AlbumDetail(DetailView):
model = Album
context_object_name = "album"
def dispatch(self, request, *args, **kwargs):
#default to asc
self.sort_order = request.GET.get("sort_order", None)
self.sort_item = request.GET.get("sort_item", None)
self.csrf_token = csrf(request)["csrf_token"]
return super(AlbumDetail, self).dispatch(request, *args, **kwargs)
def get_context_data(self, **kwargs):
#Call the base implementation first to get a context
context = super(AlbumDetail, self).get_context_data(**kwargs)
#Add in the required extra info: album_songs, ordered by
#sequence_num
#select_related is to query the database for all songs at once, here
#in the view, to prevent the template from pin-pricking the database
#in each for loop iteration. For large datasets, this is critical.
context['album_songs'] = kwargs["object"].albumsong_set.order_by('sequence_num').select_related("song")
context["url_params"] = get_url_param_string_from_params(
sort_item=self.sort_item,
sort_order=self.sort_order,
csrf_token=self.csrf_token)
return context
专辑列表.html
{% extends "base.html" %}
{% load bj_filters %}
{% block title %}Billy Joel Album Browser{% endblock %}
{% block sidebar %}
<UL>
<LI><a href="{% url 'album_list' %}{{ url_params }}">All albums</A></LI>
<LI><a href="/admin/">Admin</A></LI>
</UL>
{% endblock %}
{% block content %}
<TABLE ALIGN="center" WIDTH="100%" BORDER="1" CELLSPACING="0" CELLPADDING="4" BGCOLOR="#EEEEEE"><TR ALIGN="center" VALIGN="middle">
{% if user.is_authenticated %}
<TD>My profile (<a href="{% url 'accounts_logout' %}">Logout</A>)</TD>
{% else %}
<TD><a href="{% url 'accounts_login' %}">Login</A> to view your favorites</TD>
{% endif %}
</TR></TABLE>
<H1>Billy Joel Album Browser</H1>
<!--
<P>url_params={{ url_params }}</P>
-->
{% if albums.count > 0 %}
<P>Officiality: <IMG SRC="/static/images/major.jpg" height="20"/>=Major studio release, <IMG SRC="/static/images/minor.jpg" height="20"/>=Official release, <IMG SRC="/static/images/unofficial.jpg" height="20"/>=Unofficial</P>
<TABLE ALIGN="center" WIDTH="100%" BORDER="1" CELLSPACING="0" CELLPADDING="4" BGCOLOR="#EEEEEE"><TR ALIGN="center" VALIGN="middle">
<TD><B><U><a href="{% url 'album_list' %}?sort_item=title&sort_order=
{% if sort_item == 'pub_date' %}asc{% else %}
{{ sort_order|multival_to_str:'asc,dsc->dsc,asc,dsc' }}
{% endif %}
&csrf_token={{ csrf_token }}">Title</A></U></B><BR><I><FONT SIZE="-1">(click a title to view its song list)</FONT></I></TD>
<TD><B><U><a href="{% url 'album_list' %}?sort_item=pub_date&sort_order=
{% if sort_item == 'title' %}asc{% else %}
{{ sort_order|multival_to_str:'asc,dsc->dsc,asc,dsc' }}
{% endif %}
&csrf_token={{ csrf_token }}">Released</A></U></B></TD>
<TD>Officiality</TD>
<TD>Concert</TD>
<TD>Wiki</TD>
<TD>Favorite?</TD>
{% for album in albums %} <!-- No colon after "albums" -->
</TR><TR>
<TD VALIGN="top">
{% if album.thumbnail %}
<img src="/static/{{ album.thumbnail }}" width="25"/>
{% else %}
<img src="/static/images/white_block.jpg" width="25"/>
{% endif %}
<a href="/albums/get/{{ album.id }}{{ url_params }}">{{ album.title }}</a>
{% if album.description %}
<BR/><FONT SIZE="-1"><I>{{ album.description|truncatewords:10 }}</I></FONT>
{% endif %}
<TD>{{ album.pub_date|date:"m/y" }}</TD>
<TD><IMG SRC="/static/images/{{ album.officiality|multival_to_str:"J,I,U->major,minor,unofficial,broken_image"}}.jpg" height="20"/></TD>
<TD>{{ album.is_concert|yesno:"Yes,No" }}</TD>
<TD><A HREF="{{ album.main_info_url }}">Wiki</A></TD>
<TD><I>n/a {{ is_favorite }}</I></TD>
{% endfor %}
</TR></TABLE>
{% else %}
<P><I>There are no albums in the database.</I></P>
{% endif %}
{% endblock %}
请您参考如下方法:
M2M 关系是全新创建的表格。他们有一个唯一的名字，并且有两个外键。创建复合键，因此直接和相关模型组合是唯一的。
当你这样做时:
class Topping(models.Model):
name = ...
class Pizza(models.Model):
name = ...
toppings = models.ManyToManyField(Topping, related_name="pizzas")
#not including a related_name will generate a "pizza_set" related name.
出现一个描述关系的新表，带有一个内部名称。该表有一个 pizza_id 和一个 topping_id 外键，以及一个包含这两个字段的复合唯一键。您不能也不应该预测此类表的名称。
另一方面，如果您想要访问关系并可能声明更多字段，您可以:
class Topping(models.Model):
name = ...
class Pizza(models.Model):
name = ...
toppings = models.ManyToManyField(Topping, related_name="pizzas", through="PizzaAndTopping")
#not including a related_name will generate a "pizza_set" related name.
class PizzaAndTopping(models.Model):
more_data = models.TextField()
pizza = models.ForeignKey(Pizza, null=False)
topping = models.ForeignKey(Topping, null=False)
class Meta:
unique_together = (('pizza','topping'),)
请注意我是如何添加 through 参数的。现在您可以控制中间表但是您不能从关系中添加或删除模型。这意味着，使用这种方法您不能:
Pizza.objects.get(pk=1).toppings.append(Topping.objects.get(pk=2))
也不能删除，也不能在生命的Topping面做这些操作。
如果您想添加或删除 toppin-pizza 关系，您必须直接在 PizzaAndTopping 关系中进行。
如果您想知道当前用户是否将任何歌曲标记为他们的最爱，您应该预取 关系。在 Django 1.7 中，您可以使用自定义过滤器预取 M2M 相关字段:您可以使用 Prefetch 对象获取所有相册，并且仅获取当前用户的查询。请参阅有关预取的官方文档 here .
Antoher 解决方案包括:
- 获取当前用户最喜欢的专辑列表:
ulist = user.album_set.all() - 获取专辑的当前页面:
_list = Album.objects.all()[0:20] 获取用户相册的值:
ulist = ulist.values_list('id', flat=True)[1, 2, 4, 5, 10, ...] #you'll get a list of ids当遍历页面中的每个相册时，您测试
ulist 中的 currentAlbum.id并打印不同的消息(是或否)。
