4. [Django入门-聚合](聚合.md)

5. [Django入门-URL调度器](URL调度器.md)

**不支持负索引**

>>> Blog.objects.all()[:5]

<QuerySet [<Blog: b1>, <Blog: blog2>]>

通过关键字参数的形式(field__lookuptype=value)传递给QuerySet的filter(),get()等方法。比如：

Entry.objects.get(headline__contains='Lennon')

* exact:完全匹配。

* iexact:不区分大小写的完全匹配。

* contains:等价于like语句。

* in:等价于in语句。

Entry.objects.filter(id__in=[1, 3, 4])

inner_qs = Blog.objects.filter(name__contains='Cheddar')

entries = Entry.objects.filter(blog__in=inner_qs)

* gt: 大于。

* gte: 大于或等于。

* lt: 小于。

* lte: 小于或等于。

* startswith：同python str.startswith(),区分大小写。

* istartswith: 同python str.startswith(),不区分大小写。

* endswith/iendswith: 原理同上。

* range：

import datetime

start_date = datetime.date(2005, 1, 1)

end_date = datetime.date(2005, 3, 31)

Entry.objects.filter(pub_date__range=(start_date, end_date))

* 其他date,year,month,week,day等。

>>> Entry.objects.filter(blog__name='b1')

<QuerySet [<Entry: entry1 headline>]>

>>> Blog.objects.filter(entry__headline='entry1 headline')

<QuerySet [<Blog: b1>]>

>>> from django.db.models import F

>>> from datetime import timedelta

>>> Entry.objects.filter(mod_date__gt=F('pub_date') + timedelta(days=3))

from django.db.models import Q

Q(question__startswith='Who') | Q(question__startswith='What')

Poll.objects.get(

Q(question__startswith='Who'),

Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))

)

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

Entry.objects.filter(pub_date__year=2007).update(headline='Everything is the same')

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

>>> e.blog

>>> b = Blog.objects.get(id=1)

>>> b.entry_set.all()

from django.db import models

class Author(models.Model):

name = models.CharField(max_length=100)

age = models.IntegerField()

class Publisher(models.Model):

name = models.CharField(max_length=300)

class Book(models.Model):

name = models.CharField(max_length=300)

pages = models.IntegerField()

price = models.DecimalField(max_digits=10, decimal_places=2)

rating = models.FloatField()

authors = models.ManyToManyField(Author)

publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE)

pubdate = models.DateField()

class Store(models.Model):

name = models.CharField(max_length=300)

books = models.ManyToManyField(Book)

>>> Book.objects.count()

>>> Book.objects.filter(publisher__name='BaloneyPress').count()

>>> from django.db.models import Avg

>>> Book.objects.all().aggregate(Avg('price'))

{'price__avg': 34.35}

>>> from django.db.models import Max

>>> Book.objects.all().aggregate(Max('price'))

{'price__max': Decimal('81.20')}

>>> from django.db.models import FloatField

>>> Book.objects.aggregate(price_diff=Max('price', output_field=FloatField()) - Avg('price'))

{'price_diff': 46.85}

>>> from django.db.models import Count

>>> pubs = Publisher.objects.annotate(num_books=Count('book'))

>>> pubs

<QuerySet [<Publisher: BaloneyPress>, <Publisher: SalamiPress>, ...]>

>>> pubs[0].num_books

>>> from django.db.models import Q

>>> above_5 = Count('book', filter=Q(book__rating__gt=5))

>>> below_5 = Count('book', filter=Q(book__rating__lte=5))

>>> pubs = Publisher.objects.annotate(below_5=below_5).annotate(above_5=above_5)

>>> pubs[0].above_5

>>> pubs[0].below_5

>>> pubs = Publisher.objects.annotate(num_books=Count('book')).order_by('-num_books')[:5]

>>> pubs[0].num_books

* **通过在 QuerySet 后添加 aggregate() 子句来计算 QuerySet 对象的汇总值。**

* 传递给aggregate()的参数描述了我们要计算的聚合值。

>>> Book.objects.aggregate(average_price=Avg('price'))

{'average_price': 34.35}

**使用 annotate() 子句可以生成每一个对象的汇总。当指定 annotate() 子句，QuerySet 中的每一个对象将对指定值进行汇总。**

** aggregate()s是字句，返回的是一个字典；annotate()不是终端子句,它返回的还是一个QuerySet。**

>>> q = Book.objects.annotate(num_authors=Count('authors'))

>>> q[0].num_authors

>>> q[1].num_authors

import multiprocessing

import os

import re

import logging.handlers

import time

import signal

def term(sig_num, addtion):

mylog.info('term current pid is %s, group id is %s' % (os.getpid(), os.getpgrp()))

os.killpg(os.getpgid(os.getpid()), signal.SIGKILL)

def log_record(log_filename):

"""

dir_path = os.path.split(__file__)[0]

logdir = os.path.join(dir_path, 'log')

try:

os.makedirs(logdir, exist_ok=True)

except FileExistsError:

pass

myapp = logging.getLogger(os.path.basename(log_filename))

myapp.setLevel(logging.DEBUG)

# 按照每天一个日志，保留最近14个

filehandler = logging.handlers.TimedRotatingFileHandler(

filename='%s/%s' % (logdir, os.path.basename(log_filename)),

when='midnight', interval=1, backupCount=14)

filehandler.suffix = '%Y%m%d.log'

filehandler.extMatch = re.compile(r'^\d{8}.log$') # 只有填写了此变量才能删除旧日志

filehandler.setFormatter(logging.Formatter('%(asctime)s %(message)s'))

myapp.addHandler(filehandler)

# 让日志输出到console

console = logging.StreamHandler()

console.setLevel(logging.INFO)

console.setFormatter(logging.Formatter('%(asctime)s %(message)s'))

myapp.addHandler(console)

return myapp

process_list = []

mylog = log_record('test')

class DataDeal(multiprocessing.Process):

def __init__(self):

multiprocessing.Process.__init__(self)

pass

def run(self):

while True:

mylog.info('ID:{} running....'.format(os.getpid()))

time.sleep(3)

if __name__ == '__main__':

signal.signal(signal.SIGTERM, term)

mylog.info('主进程ID:{}'.format(os.getpid()))

for _ in range(3):

p = DataDeal()

process_list.append(p)

mylog.info(process_list)

for p in process_list:

p.daemon = True

p.start()

for p in process_list:

p.join()