dao7

public class UserDao
{
    private NpgsqlDataSource dataSource;

    private UserDao(NpgsqlDataSource dataSource)
    {
        this.dataSource = dataSource;
    }

    public User findById(int id)
    {
        var command = newDataSource().CreateCommand("SELECT * FROM TABLE WHERE ID = {id}");
        // execute command etc.
    }

    public User findByFirstName(string firstName)
    {
        var command = newDataSource().CreateCommand("SELECT * FROM TABLE WHERE ID = {firstName}");
        // execute command etc.
    }
}