Pymongo游标迭代的替代方法 [英] Alternative for Pymongo cursor iteration

问题描述

我经历了许多游标迭代问题，但没有发现任何可以解决我问题的方法.

I went through many cursor iterationn questions, but saw nothing which can solve my problem.

我有一个格式为

[{book:'A', author:'John'}, {book:'B', author:'Tony'}, {book:'C', author:'John'}...]

可能有同一作者的多本书.

Multiple books for same author possible.

我需要2个数组

authors = ['John','Tony','John']
books = ['A','B','C']

相应元素在两个数组中的索引相同.

where corresponding elements falls at same index in both arrays.

现在我可以通过游标迭代来获取它.

Now I am getting it by cursor iteration.

authors =[]
books =[]
cursor = collection.find()
for elem in cursor:
  authors.append(elem['author'])
  books.append(elem['book'])

但这很慢. 我有成千上万份文件. 是否还有其他类似查询的方法可以更快地获得结果.

But this is very slow. I have thousands of documents. Are there any other ways like queries to achieve the result faster.

推荐答案

可以执行汇总查询以收集所有作者和书籍. 例如

An aggregation query can be performed to collect all authors and books. e.g.

pipeline = [
    {
        '$group': { 
            '_id': None, 
            'authors': { '$push': '$author' }, 
            'books': { '$push': '$book' } 
        } 
    }
]

result = collection.aggregate(pipeline))

In [2]: print(result)
[{'_id': None, 'authors': ['John', 'Tony', 'John'], 'books': ['A', 'B', 'C']}]

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