Filter an array of datetime given the start and end date in pymongo

Question

I'm having a problem when i go to filter an array of dates using "$gte" and "$lte" on pymongo. I leave you a piece of code to better understand the problem.

import datetime
from pymongo import MongoClient
 

client = MongoClient('mongodb://localhost:27017')
db = client["AirQuality"]
demo = db["demo"]


demo.save({
    "devId": 1,
    "samples": [
        {"value":3, "datetime":datetime.datetime(2021, 3, 4, 20, 15, 22)},
        {"value":6, "datetime":datetime.datetime(2021, 3, 4, 22, 35, 12)},
        {"value":2, "datetime":datetime.datetime(2021, 3, 6, 10, 15, 00)}
    ]
})

and I would like to filter the values for a particular range:

start = datetime.datetime(2021, 3, 4, 22, 00, 00)
end = datetime.datetime(2021, 3, 5, 2, 26, 49)
list(demo.find( { 'samples.datetime': {  "$gte":start, "$lte":end } } ))

the output is as follows:

[{'_id': ObjectId('604353efad253df2602dfaf9'), 'devId': 1, 'samples': [{'value': 3, 'datetime': datetime.datetime(2021, 3, 4, 20, 15, 22)}, {'value': 6, 'datetime': datetime.datetime(2021, 3, 4, 22, 35, 12)}, {'value': 2, 'datetime': datetime.datetime(2021, 3, 6, 10, 15)}]}]

but I expect:

[{'_id': ObjectId('604353efad253df2602dfaf9'), 'devId': 1, 'samples': [{'value': 6, 'datetime': datetime.datetime(2021, 3, 4, 22, 35, 12)}]}]

Where am I doing wrong? Even if I apply a filter on "value" it doesn't work, so I believe the error is in the query! Thanks! 🙏

Answer 1

Solved with aggregation:

result = demo.aggregate([
    {
    "$project": {
        "samples": {
            "$filter": {
                "input": "$samples",
                "as": "item",
                "cond": {  
                    "$and":[
                        { "$gte": [ "$$item.datetime", start ] }, 
                        { "$lte": [ "$$item.datetime", end ] }
                    ]}
            }
        }
    }
    }
])

list(result)

that return:

[{'_id': ObjectId('604353efad253df2602dfaf9'), 'samples': [{'value': 6, 'datetime': datetime.datetime(2021, 3, 4, 22, 35, 12)}]}]