How to rewrite aggregation function with map-reduce in python

Working with Data
,
1

I need help with writing function with map-reduce. I have such collection and aggregation function with it:

import pymongo

db_client = pymongo.MongoClient("mongodb://localhost:27017/")

current_db = db_client["pyloungedb"] 

collection2 = current_db["Abonement bought"]

abonement_bought = [
    {'ID': 1000,'client_id': 2 , 'price': 10,'client': 'Petras Petraitis','start_date': '2022.10.14','end_date': '2022.10.14'},
    {'ID': 1000, 'client_id': 1, 'price': 30,'client': 'Jonas Jonaitis','start_date': '2021.09.14','end_date': '2022.10.14'},
    {'ID': 1002, 'client_id': 3, 'price': 300,'client': 'Monika Mokaite','start_date': '2020.10.14','end_date': '2021.10.14'}
]

ins_result = collection2.insert_many(abonement_bought)  
print(ins_result.inserted_ids)

agg_result= collection2.aggregate( 
    [{ 
    "$group" :{
        "_id" : "$ID",
        "Total" : {"$sum" : 1},
        "revenue":{"$sum" : "$price"}}}
    
        
    ]) 
for i in agg_result: 
    print(i)

I have to rewrite this with map-reduce function. Note: var doesn’t work, so I have a code, which should work, just I get empty result after printing it

def mapReduce():
    mapf = "function(){emit(this.$ID, this.$price)}"
    reducef = "function(k, v) { return Array.sum(v) }" 
    result = current_db.command(
        'mapReduce',  
        'collection2',  
        map=mapf,  
        reduce=reducef,  
        out={'inline': 1})

    print(result)

mapReduce()

Output: {‘results’: , ‘ok’: 1.0}

Using JupyterLab Python

2

Welcome to the MongoDB Community @Laura_7777 !

Please note that Map-Reduce has been deprecated as of MongoDB 5.0, and an Aggregation Pipeline is the recommended approach for performance and usability.

I assume you have academic interest in converting your aggregation pipeline to a legacy equivalent.

The map and reduce functions are implemented in JavaScript, so the aggregation syntax of $variable will not work.

You need to reference field paths directly, similar to:

mapf = “function(){emit(this.ID, this.price)}”

The functions you are creating are essentially the same as Map-Reduce Examples in the MongoDB documentation if you would like a working reference to start from.

Regards,
Stennie