This demonstration presents FlexPref, a framework implemented inside the DBMS query processor that enables efficient and extensible preference query processing. FlexPref provides query processing support inside the database engine for a wide-array of preference evaluation methods (e.g., skyline, top-k, k-dominance, k-frequency) in a single extensible code base. Integration with FlexPref is simple, involving the registration of only three functions that capture the essence of the preference method. Once integrated, the preference method "lives" at the core of the database, enabling the efficient execution of preference queries involving common database operations (e.g, selection, join). Functionality of FlexPref, implemented inside PostgreSQL, is demonstrated through the implementation and use of several state-of-the-art preference methods in a real application scenario.