DBRef('bar', ObjectId('6a73061f8f257c0343126b85'), 'foo')

DBRef('foo.bar', ObjectId('6a73061f8f257c0343126b85'))

Env: Python 3
python -m pip install pymongo

from pymongo import MongoClient
from bson import DBRef, ObjectId
from bson.codec_options import CodecOptions
from bson.raw_bson import RawBSONDocument
import bson

client = MongoClient("mongodb://localhost:27017/")
db = client["testdb"]

db.drop_collection("foo.bar")
db.drop_collection("baz")

# 1. Insert a document into a collection whose name itself contains a dot.
inserted = db["foo.bar"].insert_one({"name": "hello"})
target_id = inserted.inserted_id
print("Inserted into 'foo.bar':", target_id)

# 2. Build a DBRef pointing at that collection, using ONLY collection + id
#    (no database arg) -- this is the correct way to reference it.
ref = DBRef("foo.bar", target_id)
print("Constructed DBRef:", ref)
print("  ref.collection:", ref.collection)
print("  ref.database:", ref.database)

# 3. Store the DBRef in another document and read it back.
db["baz"].insert_one({"ref": ref})
readback = db["baz"].find_one()
print("Read back via pymongo:", readback)
print("  readback['ref'].collection:", readback["ref"].collection)
print("  readback['ref'].database:", readback["ref"].database)

# 4. Inspect the raw BSON bytes actually stored on disk, bypassing
#    pymongo's automatic DBRef decoding, to prove nothing got split.
raw_coll = db.get_collection("baz", codec_options=CodecOptions(document_class=RawBSONDocument))
raw_doc = raw_coll.find_one()
print("Raw BSON bytes:", raw_doc.raw)
print("Decoded raw BSON:", bson.decode(raw_doc.raw))

Inserted into 'foo.bar': 6a74f7612f58af1a5a376b87
Constructed DBRef: DBRef('foo.bar', ObjectId('6a74f7612f58af1a5a376b87'))
  ref.collection: foo.bar
  ref.database: None
Read back via pymongo: {'_id': ObjectId('6a74f7612f58af1a5a376b88'), 'ref': DBRef('foo.bar', ObjectId('6a74f7612f58af1a5a376b87'))}
  readback['ref'].collection: foo.bar
  readback['ref'].database: None
Raw BSON bytes: b'C\x00\x00\x00\x07_id\x00jt\xf7a/X\xaf\x1aZ7k\x88\x03ref\x00(\x00\x00\x00\x02$ref\x00\x08\x00\x00\x00foo.bar\x00\x07$id\x00jt\xf7a/X\xaf\x1aZ7k\x87\x00\x00'
Decoded raw BSON: {'_id': ObjectId('6a74f7612f58af1a5a376b88'), 'ref': DBRef('foo.bar', ObjectId('6a74f7612f58af1a5a376b87'))}

DBRef('foo.bar', ObjectId('6a74f7612f58af1a5a376b87'))