about foreignKey

#關係對象#

from django.db import models

class Blog(models.Model):

    name = models.CharField(max_length=100)

    tagline = models.TextField()

    def __str__(self):

        return self.name

class Author(models.Model):

    name = models.CharField(max_length=50)

    email = models.EmailField()

    def __str__(self):

        return self.name

class Entry(models.Model):

    blog = models.ForeignKey(Blog)

    headline = models.CharField(max_length=255)

    body_text = models.TextField()

    pub_date = models.DateTimeField()

    authors = models.ManyToManyField(Author)

    def __str__(self):

        return self.headline

例如，b是Blog的對象， b.entry_set就能夠得到Entry的對象，就能夠操做  

1 Entry.objects.filter(blog__name__exact='Beatles Blog')，查找blog的對象的數據

2 Blog.objects.filter(entry__headline__contains='Lennon')， 反過來也能夠

3 select_related(),表示能夠把第一次查找的數據加入到緩存，第二次查找就到緩存裏面查找

   e = Entry.objects.select_related().get(id=2)

   print e.blog

   print e.blog

4. XXX_set  至關於得到XXX表的對象(必須得有一個類的實例，若是用Blog.entry_set, 發生錯誤)

   b = Blog.objects.get(id=1)

   b.entry_set.all() # Returns all Entry objects related to Blog.

    b.entry_set is a Manager that returns QuerySets.

   b.entry_set.filter(headline__contains='Lennon')

   b.entry_set.count()

5. related_name 參數

   能夠重載」XXX_set」名字.舉例,若是把」Entry」模型修改成」blog =ForeignKey(Blog, related_name=’entries’)」

6. get_FOO_display()

   GENDER_CHOICES = (

    ('M', 'Male'),

    ('F', 'Female'),

)

class Person(models.Model):

    name = models.CharField(max_length=20)

    gender = models.CharField(max_length=1, choices=GENDER_CHOICES)

p = Person(name='John', gender='M')

p.save()

p.gender

‘M’

p.get_gender_display()

 'Male'

7. get_object_or_404()

# Get the Entry with a primary key of 3

e = get_object_or_404(Entry, pk=3)

# Get the author of blog instance e with a name of 'Fred'

a = get_object_or_404(e.authors, name='Fred')

# Use a custom manager 'recent_entries' in the search for an

# entry with a primary key of 3

e = get_object_or_404(Entry.recent_entries, pk=3)

8. get_list_or_404()

get_list_or_404 行爲與 get_object_or_404() 相同，可是它用 filter() 取代了 get() 。若是列表爲空，它將引起 Http404