MongoDB: unconditional updates?
Solution 1:
The error says it all: You can only modify multiple documents using the $ modifier operators. You probably had something like this:
> db.coll.update({ }, { a: 'b' }, false, true);
Which would normally replace the first object in the collection with { a: 'b' } if multi was false. You wouldn't want to replace all the objects in your collection with the same document!
Use the $set operator instead:
> db.coll.update({ }, { '$set': { a: 'b' } }, false, true);
This will set the a property of every document (creating it as necessary) to 'b'.