MongoDB - 打印 [英] MongoDB - Print

问题描述

我对打印一系列查询感兴趣.我有以下代码.

I am interested in printing a range of query. I have the following code.

start = datetime.datetime(2012, 2, 2, 6, 35, 6, 764) 

end = datetime.datetime(2012, 2, 2, 6, 55, 3, 381) 

for doc in db.model.find({'time': {'$gte': start, '$lt': end}}): 
    print doc 

它完成工作，打印出我插入数据的方式.

It does the job, printing out basically how I inserted the data.

我的问题是:

是否可以打印出整个查询的一个元素?例如，我希望它只打印项目或日期或插入的其他输入，而不是给我 {'time': datetime.datime(....), 'input1': ..., 'item': ...}.否则，如果我必须重新解析我已经解析的 mongodb 查询数据以放入 mongodb，这将大大减慢我的程序.

Is it possible to print out one element of the whole query? Such as, I want it to only print the item or the date or another input inserted, not give me {'time': datetime.datime(....), 'input1': ..., 'item': ...}. Otherwise, it would greatly slow my program if I had to reparse the mongodb query data I have already parsed to put into mongodb.

谢谢.

推荐答案

让我们了解一下 pymongo 的工作原理.

Let's have some basics about how pymongo works.

假设您在 Mongo 中有一些带有插入数据的集合.您想通过查询从该集合中获取数据:

Let's assume you have some collection in Mongo with inserted data. You want to get data from that collection by making queries:

cursor = db.model.find({'time': {'$gte': start, '$lt': end}})

"model" 集合对象的方法 find 返回 Cursor 对象:一个包含有关查询和查询结果的所有信息的实体.

Method find of "model" collection object returns Cursor object: an entity that holds all info about the query and query results.

于是查询完毕，下一步就是获取结果了.Mongo 查询的结果类型可能因方法而异.在我们的例子中(find 方法) - 结果是一堆 JSON 对象(迭代器对象)，它们中的每一个都由 Python 语言中的 dict 类型表示.这意味着您不必解析结果:它们已经被解析为字典.

So the query is made, and the next step is getting results. Result types of Mongo queries can differ from method to method. In our case (find method) - result is a bunch of JSON objects (iterator object), each of them is represented by dict type in Python language. It means that you don't have to parse results: they are already parsed into dicts.

关于Cursor 的另一件事:它是懒惰的.这意味着您可以按需获得结果.对于 Cursor 对象，您必须遍历它以获取使用查询获取的对象:

Another thing about Cursor: it is lazy. It means that you receive results on demand. In case of Cursor object, you must iterate through it to get object fetched with query:

for result_object in cursor:
    print result_object   # result_object is a dict that holds JSON object
    result_object['_id']  # Mongo ObjectId of the result_object
    # result_object["<field_name>"]  # Value stored in a field named <fieldname>

通常，您必须尝试阅读 Pymongo 教程:它很短而且指示整个驱动程序的工作方式.

Generally, you have to try reading Pymongo Tutorial: it's quite short and gives direction of how the whole driver works.

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