多个条件下的 Mongo DB 查询

Question

I am trying to do a simple query based on two conditions in MongoDB using pymongo.

I am using the sample restaurants data set from the tutorial documentation. I have:

from pymongo import MongoClient
import pymongo
import pandas as pd

client = MongoClient()

db = client.test

cursor = db.restaurants.find({"$and":[{'borough':"Manhattan"},{"grades":{'grade':"A"}}]}

for record in cursor:
    print record

I am just trying to print all the restaurants in Manhattan with a grade of 'B.' But this pulls back no results. I have also tried

cursor = db.restaurants.find({"borough":"Manhattan", "grades.grade":"B"})

but this will only filter by the first condition and won't filter by the "grade." It's exactly how it is laid out in the documentation but I can't get it to work.

Answer 1

The problem is in the second condition. grades is a subarray of grades , use $elemMatch :

db.restaurants.find({"$and": [{"borough": "Manhattan"}, {"grades": {"$elemMatch": {"grade": "A"}}}]})

Works for me.

Answer 2

I had a similar issue and it worked for me with the following syntax:

result = db.mycollection.find({"$and": [{"key1": value1}, {"key2": value2}]})

I have multiple records with the same value under key1 , but I want the only one with specific value on key2 . It seems to work for me.