使用pymongo过滤器数据查找与位置

Question

I want to filter data using pymongo. But I don't know how is this two methods different. The Result show first method's performance is better than second. But I already filter a query set list in my storage. Is this mongodb feature? or pymongo feature?

This Following is my example cases:

1. Use find method:(faster)

    result = pymongo.db.mycollection.find({ condition1, condition2 }) 

2. Use find method & where expressions:(slower)

    query_data = pymongo.db.mycollection.find({ condition1 }) result = query_data.where(Code("function() { return condition2}")) 

In official documentation, mentions that if can use standard operators avoiding use $where expression. Doc.

Answer 1

You've basically given the answer already yourself. The first version should be your preferred option as the second one using $where will result in slower execution times. One of the reasons for that is eg that $where will not use any indexes ( link ).

You can see the queries that the PHP driver really sends to MongoDB in the server logs by enabling logging on the server like this:

db.setLogLevel(1)

Also, once you know the precise queries you can use .explain() to compare the different execution plans.