Get container category.

Determines whether this container object is a std::map<> equivalent(when returns false) or that of hash_map<> class(when returns true). This method is not in stl, but it may be called by users because some operations are not supported by both type(map/hash_map) of containers, you need to call this function to distinguish the two types. dbstl will not stop you from calling the wrong methods of this class.

Returns true if this container is a hash container based on a Berkeley DB hash database; returns false if it is based on a Berkeley DB btree database.