Issue
I am having trouble allowing MongoDB to generate an _id for embedded documents. Even though I can add the embedded object and specify my own _id, leaving _id blank is causing an error. I need help letting MongoDB generate a unique _id for embedded documents.
Resolution
If you're trying to let MongoDB automatically generate a unique _id for embedded documents using the $push operation, you might run into an error if you leave the _id field blank. Unfortunately, MongoDB doesn't create unique _id values for embedded documents automatically.
Instead of using ObjectId(''), which won’t work, you should manually generate a unique _id for each embedded document. You can do this by using new ObjectId() to create a new identifier whenever you insert an embedded document.