MongoDB change field type in array

Question

I've documents with the following structure:

> db.orders.find().limit(1).pretty()
{
        "_id" : ObjectId("5846bf0e141be215b814f64a"),
        "date_add" : ISODate("2016-10-10T11:55:24Z"),
        "associations" : {
                "order_rows" : [
                        {
                                "product_id" : "31",
                                "product_quantity" : "1",
                        },
                        {
                                "product_id" : "133",
                                "product_quantity" : "1",
                        }
                ]
        },
 }

while I was able to change the "date_add" field from String to ISODate with the help of the already answered questions on stackoverflow I'm stuck with:

How to change the field type of "product_quantity" to Integer?

I've tried the following in the mongo shell:

db.orders.find().forEach(function(x){
x.associations.order_rows.product_quantity = new NumberInt(x.associations.order_rows.product_quantity);
db.orders.save(x); 
});

I then tried to use PyMongo and while I was able to extract the document and use the dictionary methods and a for loop to iterate over the list and change the value, I've no idea how to update the document back in the database.

A Solution in the mongo shell or python would be of tremendous help.

Thank you for your time and effort!

you're right. should've searched more thoroughly although my main problem was how to get to the element in the list. — Sven Tenscher
– Sven Tenscher, Commented Dec 12, 2016 at 8:47

A. Jesse Jiryu Davis · Accepted Answer · 2016-12-09 23:30:43Z

1

Use replace_one, with the document's _id as the criterion:

from pymongo import MongoClient

collection = MongoClient().test.c

# Sort to avoid seeing a doc multiple times if the update causes it to move.
for doc in collection.find().sort('_id'):
    rows = doc.get('associations', {}).get('order_rows', [])
    for row in rows:
        if 'product_quantity' in row:
            row['product_quantity'] = int(row['product_quantity'])

    collection.replace_one({'_id': doc['_id']}, doc)

answered Dec 9, 2016 at 23:30

A. Jesse Jiryu Davis

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