How can you create a single field index for a collection?

Creating an index in MongoDB is essential for optimizing query performance, and a single field index can specifically enhance lookups for queries that match a specific field. The correct approach to create a single field index is using the createIndex() method.

When you use db.coll.createIndex({fieldname: 1}), you are instructing MongoDB to create an index on the specified field (fieldname) in ascending order (indicated by the value 1). This index will help MongoDB to quickly locate documents based on values in that field, significantly speeding up query performance.

The method createIndex() is the only proper method for index creation in MongoDB, providing the necessary functionalities for defining various index types, including single field indexes, compound indexes, and more. It allows for advanced configurations as well, like unique indexes or background indexing.

Other options listed are not valid methods in MongoDB for creating an index. For instance, method names like addIndex, createSingleFieldIndex, and makeIndex do not exist in MongoDB's function set for index management. The createIndex() method is widely documented and accepted as the standard way to handle index creation in this database system.