从Django中的一系列ID中检索匹配对象的列表 [英] Retrieve a list of matching objects from a range of ids in Django

问题描述

我想实现一些相对简单的事情:我想从给定一定范围的ID的模型中检索所有对象(例如，从一本书的章节中检索第5至10行).

I want to achieve something relatively simple: I want to retrieve all objects from my model given a range of ids (for eg, retrieve the lines 5 to 10 from a book's chapter).

现在在我的views.py中，我已经:

Right now in my views.py, I've:

def line_range(request, book_id, chapter_id, line_start, line_end):
   book_name = get_object_or_404(Book, id = book_id)
   chapter_lines = []
   for i in range (int(line_start), int(line_end)+1):
      chapter_lines .append(Line.objects.get(book = book_id, chapter = chapter_id, line = i))
return render_to_response('app/book.html', {'bookTitle': book_name, 'lines': chapter_lines })

现在，这显然不是最优化的处理方式，因为它只能对一个数据库执行n个数据库查询.有没有办法做类似的事情:

Now, this is obviously not the most optimized way of doing things, as it would do n database queries, when it could be done in only one. Is there a way of doing something like:

def line_range(request, book_id, chapter_id, line_start, line_end):
   book_name = get_object_or_404(Book, id = book_id)
   lines_range = range (int(line_start), int(line_end)+1)
   chapter_lines = get_list_or_404(Line, book = book_id, chapter = chapter_id, line = lines_range)
return render_to_response('app/book.html', {'bookTitle': book_name, 'lines': chapter_lines })

从理论上讲，这将生成更好的数据库查询(用1代替n)，并且应该在性能上更好.当然，这种语法不起作用(期望一个整数，而不是一个列表).

This would in theory generate a much better database query (1 instead of n) and should be better performance wise. Of course, this syntax does not work (expecting an integer, not a list).

谢谢！

推荐答案

我认为您想要 __ range :

I think you want __range:

范围测试(含).

Range test (inclusive).

示例:

开始日期= datetime.date(2005，1，1)
end_date = datetime.date(2005，3，31)
Entry.objects.filter(pub_date__range =(开始日期，结束日期))

等效于SQL:

SELECT ...在'2005-01-01'和'2005-03-31'之间的发布日期；

您可以在SQL中可以使用BETWEEN的任何地方使用范围-用于日期，数字甚至字符.

You can use range anywhere you can use BETWEEN in SQL — for dates, numbers and even characters.

所以我想你会的:

chapter_lines = get_list_or_404(..., line__range=(int(line_start), int(line_end)+1))

同样，您可以使用 __ lt ， __ gt ， __ lte ， __ gte 进行单方面比较

Likewise, you can use __lt, __gt, __lte, __gte for one-sided comparisons.

我鼓励您始终使用Django文档打开一个窗口.只要看一下，那里就会有很多很棒的信息.

I would encourage you to always keep a window open with the Django documentation. There is lots of great info there if you just look.

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