Exception on bulk insert with EmbeddedDocument as primary key

I get an exception when trying to do a bulk insert on a collection where I have defined the primary key as an embedded document.

Repro:

from mongoengine import EmbeddedDocument, StringField, Document, EmbeddedDocumentField, connect

class Key(EmbeddedDocument):
    property1 = StringField()
    property2 = StringField()

class MainDoc(Document):
    key = EmbeddedDocumentField(Key, primary_key=True)

def main():
    connect(host="mongodb://root:rootpassword@localhost:27017/test_db?authSource=admin&authMechanism=SCRAM-SHA-1&tls=false")

    docs = [MainDoc(key=Key(property1='aaa', property2='bbb')),
            MainDoc(key=Key(property1='ccc', property2='ddd')),
            MainDoc(key=Key(property1='eee', property2='fff'))]

    MainDoc.objects.insert(docs)

main()

This results in the following output:

Traceback (most recent call last):
  File "C:\Users\danielber\AppData\Roaming\JetBrains\PyCharm2022.1\scratches\scratch_6.py", line 26, in <module>
    main()
  File "C:\Users\danielber\AppData\Roaming\JetBrains\PyCharm2022.1\scratches\scratch_6.py", line 23, in main
    MainDoc.objects.insert(docs)
  File "C:\Users\danielber\venvs\styrax\lib\site-packages\mongoengine\queryset\base.py", line 385, in insert
    documents = self.in_bulk(ids)
  File "C:\Users\danielber\venvs\styrax\lib\site-packages\mongoengine\queryset\base.py", line 748, in in_bulk
    doc_map[doc["_id"]] = self._document._from_son(
TypeError: unhashable type: 'dict'

Note that the data does get inserted to the collection, it looks like it's failing in verification code after the insert.

I encountered this using Python 3.9.9, mongoengine 0.24.1.

Thanks!

Start with the bulk insert path in mongoengine/queryset/base.py, especially insert and in_bulk, using the provided MainDoc.objects.insert reproduction. Check the post-insert verification that indexes documents by _id; done means bulk insertion completes without the unhashable-dict exception and the inserted documents remain usable.