removing document from collection during find

Question

how do I delete a document during iteration (using a cursor)?

db.users.find().forEach(function(myDoc) {
    print( "user: " + myDoc.name );
    // now I'm done with it
    myDoc.remove(); // <-- this doesn't work
} );

is there a way to do it without having to do a separate search?

db.users.find().forEach(function(myDoc) {
    print( "user: " + myDoc.name );
    // now I'm done with it
    db.users.findOneAndDelete(myDoc); // <-- this does work
} );

while the later does work, it seems like doing a search after already having the document would significantly slow down the process. (Am I wrong?)

Answer 1

You can first search objects and keep _ids in an array. And then use following code to remove all the elements once.

db.users.deleteMany(
      { "_id": {$in:idArray} },
      function(err, results) {

      }
   ); 

EDIT

I found a bulk approach to do that.

var bulk = db.users.initializeUnorderedBulkOp();
bulk.find( { "_id": {$in:idArray} }).remove();
bulk.execute();

according to my experiance, you can reduce the execution time more than 10 time faster if you use bulk operations since it reduces IO operations.

Answer 2

You can use findAndModify. Read more about it here

db.collection.findAndModify({
    query: <document>,
    remove: <boolean>
});

This function will return the deleted document, which you can use to print. You can loop it until no more documents are left.

EDIT:

Another approach you can take is using find and bulkWrite(deleteMany). First find and print all the docs. Then delete them using a bulkWrite operation.

db.users.find().forEach(function(myDoc) {
    print( "user: " + myDoc.name );
});

//This is much faster than your current approach of 
//finding and deleting singe documents

db.users.bulkWrite([
    {
        removeMany: <query>
    }
]);

bulkWrite() - MongoDB