__exact 精確等于 like ‘a(chǎn)aa’
__iexact 精確等于 忽略大小寫(xiě) ilike ‘a(chǎn)aa’
__contains 包含 like ‘%aaa%’
__icontains 包含 忽略大小寫(xiě) ilike ‘%aaa%’，但是對(duì)于sqlite來(lái)說(shuō)，contains的作用效果等同于icontains。
__gt 大于
__gte 大于等于
__lt 小于
__lte 小于等于
__in 存在于一個(gè)list范圍內(nèi)
__startswith 以…開(kāi)頭
__istartswith 以…開(kāi)頭 忽略大小寫(xiě)
__endswith 以…結(jié)尾
__iendswith 以…結(jié)尾，忽略大小寫(xiě)
__range 在…范圍內(nèi)
__year 日期字段的年份
__month 日期字段的月份
__day 日期字段的日
__isnull=True/False
__isnull=True 與 __exact=None的區(qū)別

class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField()

def __unicode__(self):
return self.name

class Author(models.Model):
name = models.CharField(max_length=50)
email = models.EmailField()

def __unicode__(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 __unicode__(self):
return self.headline

這是model，有blog，author，以及entry；其中entry分別與blog與author表關(guān) 聯(lián)，entry與blog表是通過(guò) 外鍵(models.ForeignKey())相連，屬于一對(duì)多的關(guān)系，即一個(gè)entry對(duì)應(yīng)多個(gè)blog，entry與author是多對(duì)多的關(guān)系， 通過(guò)modles.ManyToManyField()實(shí)現(xiàn)。
一、插入數(shù)據(jù)庫(kù)，用save()方法實(shí)現(xiàn)，如下：
>>> from mysite.blog.models import Blog
>>> b = Blog(name=’Beatles Blog’, tagline=’All the latest Beatles news.’)
>>> b.save()

二、更新數(shù)據(jù)庫(kù)，也用save()方法實(shí)現(xiàn)，如下：
>> b5.name = ‘New name’
>> b5.save()

保存外鍵和多對(duì)多關(guān)系的字段，如下例子：
更新外鍵字段和普通的字段一樣，只要指定一個(gè)對(duì)象的正確類(lèi)型。
>>> cheese_blog = Blog.objects.get(name=”Cheddar Talk”)
>>> entry.blog = cheese_blog
>>> entry.save()

更新多對(duì)多字段時(shí)又一點(diǎn)不太一樣，使用add()方法添加相關(guān)聯(lián)的字段的值。
>> joe = Author.objects.create(name=”Joe”)
>> entry.authors.add(joe)

三、檢索對(duì)象

>>> Blog.objects

>>> b = Blog(name=’Foo’, tagline=’Bar’)
>>> b.objects
Traceback:
…
AttributeError: “Manager isn’t accessible via Blog instances.”

1、檢索所有的對(duì)象

>>> all_entries = Entry.objects.all()

使用all()方法返回?cái)?shù)據(jù)庫(kù)中的所有對(duì)象。

2、檢索特定的對(duì)象
使用以下兩個(gè)方法：
fileter(**kwargs)
返回一個(gè)與參數(shù)匹配的QuerySet,相當(dāng)于等于(=).
exclude(**kwargs)
返回一個(gè)與參數(shù)不匹配的QuerySet,相當(dāng)于不等于(!=)。

Entry.objects.filter(pub_date__year=2006)
不使用Entry.objects.all().filter(pub_date__year=2006),雖然也能運(yùn)行，all()最好再獲取所有的對(duì)象時(shí)使用。
上面的例子等同于的sql語(yǔ)句：
slect * from entry where pub_date_year=’2006′

鏈接過(guò)濾器：
>>> Entry.objects.filter(
… headline__startswith=’What’
… ).exclude(
… pub_date__gte=datetime.now()
… ).filter(
… pub_date__gte=datetime(2005, 1, 1)
… )

最后返回的QuerySet是headline like ‘What%’ and put_date2005-01-01

另外一種方法：
>> q1 = Entry.objects.filter(headline__startswith=”What”)
>> q2 = q1.exclude(pub_date__gte=datetime.now())
>> q3 = q1.filter(pub_date__gte=datetime.now())
這種方法的好處是可以對(duì)q1進(jìn)行重用。

QuerySet是延遲加載
只在使用的時(shí)候才會(huì)去訪問(wèn)數(shù)據(jù)庫(kù)，如下：
>>> q = Entry.objects.filter(headline__startswith=”What”)
>>> q = q.filter(pub_date__lte=datetime.now())
>>> q = q.exclude(body_text__icontains=”food”)
>>> print q
在print q時(shí)才會(huì)訪問(wèn)數(shù)據(jù)庫(kù)。

其他的QuerySet方法
>>> Entry.objects.all()[:5]
這是查找前5個(gè)entry表里的數(shù)據(jù)

>>> Entry.objects.all()[5:10]
這是查找從第5個(gè)到第10個(gè)之間的數(shù)據(jù)。

>>> Entry.objects.all()[:10:2]
這是查詢從第0個(gè)開(kāi)始到第10個(gè)，步長(zhǎng)為2的數(shù)據(jù)。

>>> Entry.objects.order_by(‘headline’)[0]
這是取按headline字段排序后的第一個(gè)對(duì)象。

>>> Entry.objects.order_by(‘headline’)[0:1].get()
這和上面的等同的。

>>> Entry.objects.filter(pub_date__lte=’2006-01-01′)
等同于SELECT * FROM blog_entry WHERE pub_date <= ’2006-01-01′; >>> Entry.objects.get(headline__exact=”Man bites dog”)
等同于SELECT … WHERE headline = ‘Man bites dog’;

>>> Blog.objects.get(id__exact=14) # Explicit form
>>> Blog.objects.get(id=14) # __exact is implied
這兩種方式是等同的，都是查找id=14的對(duì)象。

>>> Blog.objects.get(name__iexact=”beatles blog”)
查找name=”beatles blog”的對(duì)象，不去飯大小寫(xiě)。

Entry.objects.get(headline__contains=’Lennon’)
等同于SELECT … WHERE headline LIKE ‘%Lennon%’;

startswith 等同于sql語(yǔ)句中的 name like ‘Lennon%’,
endswith等同于sql語(yǔ)句中的 name like ‘%Lennon’.

>>> Entry.objects.filter(blog__name__exact=’Beatles Blog’)
查找entry表中外鍵關(guān)系blog_name=’Beatles Blog’的Entry對(duì)象。

>>> Blog.objects.filter(entry__headline__contains=’Lennon’)
查找blog表中外鍵關(guān)系entry表中的headline字段中包含Lennon的blog數(shù)據(jù)。

Blog.objects.filter(entry__author__name=’Lennon’)
查找blog表中外鍵關(guān)系entry表中的author字段中包含Lennon的blog數(shù)據(jù)。

Blog.objects.filter(entry__author__name__isnull=True)
Blog.objects.filter(entry__author__isnull=False,entry__author__name__isnull=True)
查詢的是author_name為null的值

Blog.objects.filter(entry__headline__contains=’Lennon’,entry__pub_date__year=2008)
Blog.objects.filter(entry__headline__contains=’Lennon’).filter( entry__pub_date__year=2008)
這兩種查詢?cè)谀承┣闆r下是相同的，某些情況下是不同的。第一種是限制所有的blog數(shù)據(jù)的，而第二種情況則是第一個(gè)filter是
限制blog的，而第二個(gè)filter則是限制entry的

>>> Blog.objects.get(id__exact=14) # Explicit form
>>> Blog.objects.get(id=14) # __exact is implied
>>> Blog.objects.get(pk=14) # pk implies id__exact
等同于select * from where id=14

# Get blogs entries with id 1, 4 and 7
>>> Blog.objects.filter(pk__in=[1,4,7])
等同于select * from where id in{1,4,7}
# Get all blog entries with id > 14
>>> Blog.objects.filter(pk__gt=14)
等同于select * from id>14

>>> Entry.objects.filter(blog__id__exact=3) # Explicit form
>>> Entry.objects.filter(blog__id=3) # __exact is implied
>>> Entry.objects.filter(blog__pk=3) # __pk implies __id__exact
這三種情況是相同的

>>> Entry.objects.filter(headline__contains=’%')
等同于SELECT … WHERE headline LIKE ‘%\%%’;

Caching and QuerySets

>>> print [e.headline for e in Entry.objects.all()]
>>> print [e.pub_date for e in Entry.objects.all()]
應(yīng)改寫(xiě)為：
>> queryset = Poll.objects.all()
>>> print [p.headline for p in queryset] # Evaluate the query set.
>>> print [p.pub_date for p in queryset] # Re-use the cache from the evaluation.、
這樣利用緩存，減少訪問(wèn)數(shù)據(jù)庫(kù)的次數(shù)。

四、用Q對(duì)象實(shí)現(xiàn)復(fù)雜的查詢

Q(question__startswith=’Who’) | Q(question__startswith=’What’)
等同于WHERE question LIKE ‘Who%’ OR question LIKE ‘What%’

Poll.objects.get(
Q(question__startswith=’Who’),
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)
等同于SELECT * from polls WHERE question LIKE ‘Who%’ AND (pub_date = ’2005-05-02′ OR pub_date = ’2005-05-06′)

Poll.objects.get(
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)),
question__startswith=’Who’)
等同于Poll.objects.get(question__startswith=’Who’, Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)))

五、比較對(duì)象

>>> some_entry == other_entry
>>> some_entry.id == other_entry.id

六、刪除

Entry.objects.filter(pub_date__year=2005).delete()

b = Blog.objects.get(pk=1)
# This will delete the Blog and all of its Entry objects.
b.delete()

Entry.objects.all().delete()
刪除所有

七、一次更新多個(gè)值

# Update all the headlines with pub_date in 2007.
Entry.objects.filter(pub_date__year=2007).update(headline=’Everything is the same’)

>>> b = Blog.objects.get(pk=1)
# Change every Entry so that it belongs to this Blog.
>>> Entry.objects.all().update(blog=b)

如果用save()方法，必須一個(gè)一個(gè)進(jìn)行保存，需要對(duì)其就行遍歷，如下：
for item in my_queryset:
item.save()

關(guān)聯(lián)對(duì)象

one-to-many
>>> e = Entry.objects.get(id=2)
>>> e.blog # Returns the related Blog object.

>>> e = Entry.objects.get(id=2)
>>> e.blog = some_blog
>>> e.save()

>>> e = Entry.objects.get(id=2)
>>> e.blog = None
>>> e.save() # “UPDATE blog_entry SET blog_id = NULL …;”

>>> e = Entry.objects.get(id=2)
>>> print e.blog # Hits the database to retrieve the associated Blog.
>>> print e.blog # Doesn’t hit the database; uses cached version.

>>> e = Entry.objects.select_related().get(id=2)
>>> print e.blog # Doesn’t hit the database; uses cached version.
>>> print e.blog # Doesn’t hit the database; uses cached version

>>> 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()

>>> b = Blog.objects.get(id=1)
>>> b.entries.all() # Returns all Entry objects related to Blog.
# b.entries is a Manager that returns QuerySets.
>>> b.entries.filter(headline__contains=’Lennon’)
>>> b.entries.count()

You cannot access a reverse ForeignKey Manager from the class; it must be accessed from an instance:
>>> Blog.entry_set

add(obj1, obj2, …)
Adds the specified model objects to the related object set.
create(**kwargs)
Creates a new object, saves it and puts it in the related object set. Returns the newly created object.
remove(obj1, obj2, …)
Removes the specified model objects from the related object set.
clear()
Removes all objects from the related object set.

many-to-many類(lèi)型：
e = Entry.objects.get(id=3)
e.authors.all() # Returns all Author objects for this Entry.
e.authors.count()
e.authors.filter(name__contains=’John’)
a = Author.objects.get(id=5)
a.entry_set.all() # Returns all Entry objects for this Author.

one-to-one 類(lèi)型：
class EntryDetail(models.Model):
entry = models.OneToOneField(Entry)
details = models.TextField()

ed = EntryDetail.objects.get(id=2)
ed.entry # Returns the related Entry object

使用sql語(yǔ)句進(jìn)行查詢：

def my_custom_sql(self):
from django.db import connection
cursor = connection.cursor()
cursor.execute(“SELECT foo FROM bar WHERE baz = %s”, [self.baz])
row = cursor.fetchone()
return row

轉(zhuǎn)載于:https://www.cnblogs.com/floodwater/p/9951017.html

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