When attempting to assign the _id property to a string during a MongoDB import, you may get the following error:

TypeError: Cannot create property `_id` on string

This error occurs when you try to manually assign _id, which is a reserved field in MongoDB. In most cases, you do not need to manually assign the _id field during the import process. When importing data into MongoDB, the database automatically assigns an _id as the unique identifier for each document.

To fix this error, you can remove the _id field from your JSON data file. MongoDB then automatically generates the _id values for each document during the import process. For example, a data.json file may look like this:

[
  { "name": "John Doe" },
  { "name": "Jane Doe" }
]

Then, when importing data.json into MongoDB, the database automatically generates the _id values needed for each document in data.json, like this:

[
  { "_id": ObjectId("6174f998f7c34a001f4efbc2"), "name": "John Doe" },
  { "_id" : ObjectId("6174f99af7c34a001f4efbc3"), "name": "Jane Doe" }
]