(lyx) Chapter Number after Part Number (Chapter 4.4 instead of Chapter 4)

Question

I know its counter-intuitive and doesn't make any sense at all, but bear with me. I am using the classic thesis style (in lyx), and the recommendation of my university ask me to do so. So currently My structure is something like this

Part 1 Introduction
  Chapter 1 AAAAA
  Chpater 2 BBBBB
  Chapter 3 CCCCC

Part 2 Something
  Chapter 4 DDDDD
  Chapter 5 EEEEE
  Chpter  6 FFFFFF

I need it turned into something like this

Part 1 Introduction
  Chapter 1.1 AAAAA
  Chpater 1.2 BBBBB
  Chapter 1.3 CCCCC

Part 2 Something
  Chapter 2.1 DDDDD
  Chapter 2.2 EEEEE
  Chpter  2.3 FFFFF

Needless to say, If the esctions and subsections can also ripple down like that That'd be great.

Any suggestions?

EDIT:

I received a suggestion to use

\renewcommand{\thechapter}{\arabic{part}.\arabic{chapter}}

The results look great. However, classic thesis does not support decimal points in chapter number (and it looks ugly).

So I looked around the net and from this Move chapter number to chapter title in classicthesis, My chapter numbers look more acceptable like this

However, the chapter numbers do not reset when we change parts.

Suggestions?

EDIT: The counterwithin command bugs out the pdf bookmark like this, and when I use the LaTeX solution, this doesn't happen.

Answer 1

A short answer, but too long for a comment and good highlighting. It is not meant to keep it.

For resetting, you have to add it the reset list (;-))

In the preamble, say after the last \usepackage{}, but before \begin{document}

\makeatletter
\@addtoreset{chapter}{part}
\makeatother

This will reset the chapter number when a new part starts!

Answer 2

You can use the chngcntr package:

\usepackage{chngcntr}
\counterwithin{chapter}{part}

both will reset the chapter counter each time a new part begins and will prefix the chapter counter with the part counter.