Python 在 Django ORM 中查询时如何将字符转换为整数？
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How do i cast char to integer while querying in django ORM?
提问by Learner_Programmer
Recently started using Django ORM.I want to execute this query
最近开始使用Django ORM。我想执行这个查询
select student_id from students where student_id like "%97318%" order by CAST(student_id as UNSIGNED) desc;
where student_id is a CharField which I want as integer for querying. I tried with
其中 student_id 是一个 CharField，我想要作为查询的整数。我试过
students.objects.filter(student_id__contains "97318").order('-student_id')
works fine. But don't know and couldn't find how to cast "student_id" to int like the actual MySQL query mentioned above with "Django ORM". should I use raw query or is there a way out? Let me know your suggestions.
工作正常。但是不知道也找不到如何将“student_id”转换为 int 就像上面提到的“Django ORM”的实际 MySQL 查询一样。我应该使用原始查询还是有出路？让我知道你的建议。
采纳答案by erikreed
An updated alternative without requiring the use of extrais the cast function (new in Django 1.10):
不需要使用的更新替代方法extra是 cast 函数（Django 1.10 中的新功能）：
>>> from django.db.models import FloatField
>>> from django.db.models.functions import Cast
>>> Value.objects.create(integer=4)
>>> value = Value.objects.annotate(as_float=Cast('integer', FloatField())).get()>
>>> print(value.as_float)
4.0
From https://docs.djangoproject.com/en/1.10/ref/models/database-functions/#cast
来自https://docs.djangoproject.com/en/1.10/ref/models/database-functions/#cast
回答by catavaran
回答by KinoP
I have tried extra()and annotate()to CAST, but they did not work well with related fields and generates JOINS resulting unexpected queryset sometimes.
我曾尝试extra()和annotate()给CAST，但他们并没有与相关领域很好地工作，并产生联接有时会造成意想不到的查询集。
What I ended up was to create a Custom Lookup.
我最终是创建一个自定义查找。
The documentation is few but can be found at hereand here
Here is my example:
这是我的例子：
@Field.register_lookup
class IntegerValue(Transform):
# Register this before you filter things, for example in models.py
lookup_name = 'int' # Used as object.filter(LeftField__int__gte, "777")
bilateral = True # To cast both left and right
def as_sql(self, compiler, connection):
sql, params = compiler.compile(self.lhs)
sql = 'CAST(%s AS UNSIGNED)' % sql
return sql, params
Then below should work:
那么下面应该工作：
students.objects.filter(student_id__int__gte="97318").order('-student_id')
