django查询表记录的十三种方法

all() 结果为queryset类型
~~~python

models.Book.objects.all()
<QuerySet [<Book: Book object>, <Book: Book object>, <Book: Book object>]>
~~~
filter() 条件查询(它下面也有很多种方法，见最下面)
~python
ret = models.Book.objects.filter(id=5)
ret
<QuerySet [<Book: Book object>]>
~
get() 得到的是一个model对象，有且只能有一个
会出现两种报错

• 1 查不到数据会报错 ：Book matching query does not exist.
• 2 返回值超过一个就报错 ：returned more than one Book — it returned 13！

>>> ret = models.Book.objects.get(id=5)
>>> ret
<Book: Book object>

exclude() 排除

1. object能够调用，models.Book.objects.exclude(book_name__startswith=’活’)
2. queryset类型数据能够调用。

>>> ret = models.Book.objects.all()
>>> ret.exclude(id=5)
<QuerySet [<Book: Book object>, <Book: Book object>]>

order_by() 排序
~~~python
models.Book.objects.all().order_by(‘-price’,’id’)

类似于mysql种的order by price desc,id asc;

~~~
reverse() 反转
~~~python
models.Book.objects.all().order_by(‘id’).reverse()

数据排序之后才能反转

~~~
count() 计数，统计返回结果的数量
~~~python

ret = models.Book.objects.all().count()
ret
3
~~~
first() 返回第一条数据，结果是model对象类型
~python
ret = models.Book.objects.all()
ret.first()
<Book: Book object>
ret.first().id
5
~
last() 返回最后一条数据，结果是model对象类型
~~~python
ret = models.Book.objects.all()
ret.last()
<Book: Book object>
ret.last().id
11

~~~
exists() 判断返回结果集是不是有数据
~~~python

ret = models.Book.objects.filter(id=999).exists()
ret
False
ret = models.Book.objects.filter(id=11).exists()
ret
True

~~~
values() (返回的queryset，里面是字典类型数据)
~~~python

ret = models.Book.objects.all().values(‘id’,’book_name’)
ret
<QuerySet [{‘id’: 5, ‘book_name’: ‘1’}, {‘id’: 6, ‘book_name’: ‘2’}, {‘id’: 11, ‘book_name’: ’23’}]>
~~~
values_list(返回的queryset,里面是数组类型数据)
~~~python
ret = models.Book.objects.all().values_list(‘id’,’book_name’)
ret
<QuerySet [(5, ‘1’), (6, ‘2’), (11, ’23’)]>

~~~
调用values或者values_list的是objects控制器,那么返回所有数据
~~~python

ret = models.Book.objects.values()
ret
<QuerySet [
{‘id’: 5, ‘book_name’: ‘1’, ‘price’: 2.0, ‘shijian’: ‘2018-03-22’, ‘press’: ‘admin’},
{‘id’: 6, ‘book_name’: ‘2’, ‘price’: 1234.0, ‘shijian’: ‘2013-3-2’, ‘press’: ‘sdf’},
{‘id’: 11, ‘book_name’: ’23’, ‘price’: 11.0, ‘shijian’: ‘2019-09-10’, ‘press’: ‘234’}]>

~~~
distinct() 去重，配置values和values_list来使用
~~~python

models.Book.objects.all().values(‘book_name’).distinct()
<QuerySet [{‘book_name’: ‘1’}, {‘book_name’: ‘2’}, {‘book_name’: ’23’}]>
~~~

filter双下划线查询

**__in** price值等于这三个里面的任意一个的对象
~~~python
Book.objects.filter(price__in=[100,200,300])
~~~
**__gt** 大于
~~~python

ret = models.Book.objects.filter(price__gt=1233)
ret.values()
<QuerySet [{‘id’: 6, ‘book_name’: ‘2’, ‘price’: 1234.0, ‘shijian’: ‘2013-3-2’, ‘press’: ‘sdf’}]>

~~~
**__gte**大于等于
~~~python

ret = models.Book.objects.filter(price__gte=2)
ret.count()
3

~~~
lt 等于
~~~python

ret = models.Book.objects.filter(price__lt=1234)
ret.count()
2

~~~
lte 小于等于
~~~python

ret = models.Book.objects.filter(price__lte=1234)
ret.count()
3

~~~
**__range** 大于等于35，小于等于38
~~~python

ret = models.Book.objects.filter(price__range=[35,38])
ret.count()
3
~~~
**__contains** 包含这个字符串的数据
~~~python
ret = models.Book.objects.filter(book_name__contains=’2′)
ret.values()
<QuerySet [{‘id’: 6, ‘book_name’: ‘2’, ‘price’: 1234.0, ‘shijian’: ‘2013-3-2’, ‘press’: ‘sdf’}, {‘id’: 11, ‘book_name’: ’23’, ‘price’: 11.0, ‘shijian’: ‘2019-09-10’, ‘press’: ‘234’}]>

~~~
**__icontains** 不区分大小写
~~~python
ret = models.Book.objects.filter(book_name__icontains=’py’)
~~~
**__startswith** 以什么开头 — endswith(以什么结尾) — istartswith(不区分大小写)
~~~python

ret = models.Book.objects.filter(book_name__startswith=’2′)
ret.values()
<QuerySet [{‘id’: 6, ‘book_name’: ‘2’, ‘price’: 1234.0, ‘shijian’: ‘2013-3-2’, ‘press’: ‘sdf’}, {‘id’: 11, ‘book_name’: ’23’, ‘price’: 11.0, ‘shijian’: ‘2019-09-10’, ‘press’: ‘234’}]>

~~~
**__year** 查询年 **__month** 月
~~~python
ret = models.Book.objects.filter(publish_date__year=’2018′)
~~~
**__isnull** 字段值为空的数据
~~~python
models.Book.objects.filter(publish_date__isnull=True)
~~~