CODEWITHSUNDEEP
mongodbmongoengine
J. Doe
J. Doe

Reputation: 23

Is it possible to delete a field with MongoEngine, without strict=False?

I've got a lot of data in MongoDB, which we access primarily via MongoEngine, and sometimes data first ended up in field F1, and then we later decided that field F2 is a better place for it, so we moved it over there, and stopped using F1.

That's convenient, but now we've got a bunch of stale (or useless) data in old F1 keys, and new documents are being created with empty F1 keys, for no reason.

While MongoDB being schemaless is convenient, I still appreciate the strict=True feature (which is on by default), and try to avoid turning it off except when absolutely necessary. I don't like turning off all the safety checks on a collection.

So is there any way to delete a field F1 from my MongoDB collection, without downtime, and without strict=False?

Is there any way with MongoEngine to say "This is an old field. You can load it (or ignore it) if it's there, but don't create it for any new documents"?

Upvotes: 2

Views: 3926

Answers (1)

matino
matino

Reputation: 17715

If I remove the field from my database first, MongoEngine will create it for any new records, until the model is updated

It's only true if you explicitly write to that field or if the field has a default value set. Otherwise the field won't exist in MongoDB.

So as first step I suggest to remove the code that writes to that field and remove the default value (or set it to None). Then it's safe to remove the field from the database.

Below a small proof:

import mongoengine

class Foo(mongoengine.Document):
    a = mongoengine.IntField()
    b = mongoengine.ListField(default=None)

f = Foo().save()
type(f.a)  # NoneType
type(f.b)  # NoneType

And the database query:

> db.foo.findOne()
{ "_id" : ObjectId("56c49ae8ee8b341b4ea02fcb") }

Upvotes: 1

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