问题
When I do this,
>>> b = Blog.objects.all()
>>> b
I get this:
>>>[<Blog: Blog Title>,<Blog: Blog Tile>]
When I query what type b is,
>>> type(b)
I get this:
>>> <class 'django.db.models.query.QuerySet'>
What does this mean? Is it a data type like dict, list, etc?
An example of how I can build data structure like a QuerySet will be appreciated.
I would want to know how Django builds that QuerySet (the gory details).
回答1:
Yes, it's just another type, built like every other type.
回答2:
A django queryset is like its name says, basically a collection of (sql) queries, in your example above print(b.query) will show you the sql query generated from your django filter calls.
Since querysets are lazy, the database query isn't done immediately, but only when needed - when the queryset is evaluated. This happens for example if you call its __str__ method when you print it, if you would call list() on it, or, what happens mostly, you iterate over it (for post in b..). This lazyness should save you from doing unnecessary queries and also allows you to chain querysets and filters for example (you can filter a queryset as often as you want to).
回答3:
A QuerySet represents a collection of objects from your database. It can have zero, one or many filters. Filters narrow down the query results based on the given parameters. In SQL terms, a QuerySet equates to a SELECT statement, and a filter is a limiting clause such as WHERE or LIMIT.
https://docs.djangoproject.com/en/1.8/topics/db/queries/
回答4:
A QuerySet is a list of objects of a given model, QuerySet allow you to read data from database
来源：https://stackoverflow.com/questions/4681202/what-is-a-django-queryset