Unable to Create or Update Nested Fields When Parent Field is null in MongoDB

_INT1 · 2024-12-18T17:30:56.725Z

Description:

When attempting to create or update nested fields using dot notation in MongoDB, if the parent field is explicitly set to null, the operation fails with an error:

sql

Cannot create field 'coordinates' in element {position: null}

This issue prevents partial updates or nested field additions in documents where parent fields are initialized as null.

Steps to Reproduce:

Insert a document with a null parent field:

{
  
  
"_id": 1,
  "position": null
}

Attempt to add or update a nested field using dot notation:

db.collection.updateOne(
  { "_id": 1 },
  { "$set": { "position. coordinates": "new value" } }
)

MongoDB throws the following error:

Cannot create field 'coordinates' in element {position: null}

Expected Behavior:

The parent field should automatically be converted into an object (i.e., {}), allowing the nested field to be created or updated without explicit reinitialization.

How Can This Be Resolved Using Dot Notation?

steevej · 2024-12-18T20:11:13.970Z

Is this expected behavior documented somewhere:

_INT1:

Expected Behavior:

The parent field should automatically be converted into an object (i.e., {})

Until a better answer shows up you could try:

db.collection.updateOne(
  { "_id": 1 , "position" : null },
  { "$set": { "position" : { "coordinates": "new value" } } }
)

which is not an answer to

_INT1:

How Can This Be Resolved Using Dot Notation?

but is a possible way to get around the limitation.

If you do not know if you are in the null vs not null situation you may create a bulkWrite with 2 ordered updateOne to cover both cases.

Alternatively, the update with aggregation syntax could be use to $set with a $cond on position:null.

steevej · 2025-01-02T14:02:09.128Z

@_INT1, more that 2 weeks ago I provided you with some alternative ways to solve your issue.

I would appreciate a followup.

Thanks in advance.