按ObjectId日期汇总MongoDB结果 [英] Aggregate MongoDB results by ObjectId date

问题描述

如何按ObjectId日期汇总MongoDB结果.示例:

How can I aggregate my MongoDB results by ObjectId date. Example:

默认光标结果:

cursor = [
    {'_id': ObjectId('5220b974a61ad0000746c0d0'),'content': 'Foo'},
    {'_id': ObjectId('521f541d4ce02a000752763a'),'content': 'Bar'},
    {'_id': ObjectId('521ef350d24a9b00077090a5'),'content': 'Baz'},
]

预计结果:

projected_cursor = [
    {'2013-09-08':
        {'_id': ObjectId('5220b974a61ad0000746c0d0'),'content': 'Foo'},
        {'_id': ObjectId('521f541d4ce02a000752763a'),'content': 'Bar'}
    },
    {'2013-09-07':
        {'_id': ObjectId('521ef350d24a9b00077090a5'),'content': 'Baz'}
    }
]

这是我目前在PyMongo中用于实现这些结果的方法，但是它很凌乱，我想看看如何使用MongoDB的聚合框架(甚至是MapReduce)来做到这一点:

This is what I'm currently using in PyMongo to achieve these results, but it's messy and I'd like to see how I can do it using MongoDB's aggregation framework (or even MapReduce):

cursor = db.find({}, limit=10).sort("_id", pymongo.DESCENDING)
messages = [x for x in cursor]
this_date = lambda x: x['_id'].generation_time.date()
dates = set([this_date(message) for message in messages])
dates_dict = {date: [m for m in messages if this_date(m) == date] for date in dates}

是的，我知道最简单的方法是向每个记录添加一个新的日期字段，然后以此为依据进行汇总，但这不是我现在想做的.

And yes, I know that the easiest way would be to simply add a new date field to each record then aggregate by that, but that's not what I want to do right now.

谢谢！

推荐答案

所以这不能直接回答我的问题，但是我确实找到了一种更好的方法，可以使用Python的setdefault替换上面所有的lambda废话:

So this doesn't answer my question directly, but I did find a better way to replace all that lambda nonsense above using Python's setdefault:

d = {}
for message in messages:
    key = message['_id'].generation_time.date()
    d.setdefault(key,[]).append(message)

感谢@raymondh暗示了PyCon谈话:

Thanks to @raymondh for the hint in is PyCon talk:

将代码转换为漂亮的惯用Python

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