Update multiple fields in mongo based on their existence

Question

I am trying to copy selected fields from collection 'a' to collection 'b'. I would like to set multiple fields on b based on whether they exist in a. i.e If the field dosen't exist in 'a; then I don't want to set it in 'b'.

This is what I'm trying

b.update_one(
              {"_id": xyz},
              {"$set": {"name": a['name'],
                        "lastname": a.get('lastname', None)}})

This gives me None is lastname doesn't exist. I don't want lastname to be updated at all if there is not lastname in 'a'. Is there any other alternative apart from using 2 set statements?

Tomáš Linhart · Accepted Answer · 2019-09-28 12:13:20Z

1

Prepare the update definition beforehand. For example, suppose a has this value:

a = {
    'name': 'John'
}

Then define the update so that it only contains fields from a that you are interested in (and that are present in a):

update = {
    'name': a.get('name'),
    'lastname': a.get('lastname')
    ...
}
update = {k: v for k, v in update.items() if v is not None}

Now perform the update:

b.update_one(
    {"_id": xyz},
    {"$set": update}
)

answered Sep 28, 2019 at 12:13

Tomáš Linhart

10.2k1 gold badge30 silver badges42 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Update multiple fields in mongo based on their existence

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related