在django过滤器中使用dateadd [英] Using dateadd in django filter

问题描述

我有一个模型，按开始日期和持续时间（天）定义订阅期限：

I have a model that defines subscription periods by start date and duration (in days):

class SubscriptionProduct(models.Model):    
    start_date = models.DateField()
    duration = models.IntegerField()

我需要能够筛选当前活动的订阅，例如 start_date<现在< start_date + duration

I need to be able to filter subscriptions that are currently active, e.g. start_date < now < start_date+duration

我找不到django的方法。我可以使用使用Postgres'DATEADD等同于INTERVAL的原始SQL语句，但我更喜欢使用内置的和非特定的数据库。

I can't find the django way to do it. I can use raw SQL statements that use postgres' DATEADD equivalent of INTERVAL but i'd prefer to use something builtin and non db specific.

我认为我很想看用于dateadd注释方法。如下：

I assume ideally i'm looking for a dateadd annotation method. Something like:

SubscriptionProduct.objects.annotate(end_date=DateAdd('start_date','duration').filter(start_date__lt=datetime.now, end_date__gte=datetime.now)

推荐答案

最终编写了一个自定义的Func表达式，它精确地执行了我正在寻找的内容。
这是非常Postgresql特定的，有点黑客，但它可以工作，即使在比上面所示的更复杂的查询中使用。

I ended up writing a custom Func expression that does exacly what I was looking for. This is very Postgresql specific and a bit hacky but it works, even when used in more complex queries than the one illustrated above.

class DateAdd(Func):
    """
    Custom Func expression to add date and int fields as day addition
    Usage: SubscriptionProduct.objects.annotate(end_date=DateAdd('start_date','duration')).filter(end_date__gt=datetime.now)
    """
    arg_joiner = " + CAST("
    template = "%(expressions)s || ' days' as INTERVAL)"
    output_field = DateTimeField()

请注意，我不得不按照f执行arg_joiner技巧或两个字段名称在subselect表达式

Note that I had to do the arg_joiner trick in order for both field names to be resolved properly when used in subselect expressions

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