MongoCollection.createIndex

string createIndex(T)(T keys,
		 IndexOptions indexOptions =  IndexOptions.init,
		 CreateIndexOptions options =  CreateIndexOptions.init) if (!is(Unqual!T ==  IndexModel))

@safe

Convenience method for creating a single index. Calls createIndexes

Supports any kind of document for template parameter T or a IndexModel.

Parameters

keys a IndexModel or type with integer or string fields indicating index direction or index type.

string createIndex(const  IndexModel keys,
		 CreateIndexOptions options =  CreateIndexOptions.init)

@safe

ditto