ActiveRecord method

Hello.I have a question. I am making chat application to practice RoR.

I have three models. User, Chat, and Message.
The relationship is that User has many chats(it means chat's host) and many
message,s Chat has many messages.

Now I want to create a lobby page like this.

This page shows all chats sorted by the last message's created_at. each chat
shows who is chat's host, and what the last message is.

Is there any good way to get resource by ActiveRecord's method?

Sorry, I don't understand the question.
Have you worked right through some tutorials (railstutorial is good
and is free to use online) to understand the basics of rails? If not
then I suggest you do this.

Besides, the amount of messages will be huge,so is there good way to get all
chats which have the last message by loading LIMIT 1 message?

You can fetch just the first record of a query by using .first