authenticate: function(username, password){
      return this.find({'account.username': username}).first(function(user){
        if(user.account.username == user.account.username && user.account.password == password.md5) this.result(user);
        else this.result(false);
      });
    },

    existByUsername: function (username) {
      return this.find({'account.username': username}).first(function(user){
        if(user.account.username.length) this.result(user);
        else this.result(false);
      });
    },