There is an expression "cache an object" when caching, but is this object an object-oriented object?

Does caching objects mean caching Text objects?

Yes, the object in that case is considered synonymous with the instance.

text=Text.first
Rails.cache.write("some_cache_key", text)

However, if you write like this, you may misunderstand that "data retrieved from DB" or "instantiated objects" are cached.

In fact, it doesn't matter if it's a string, a number, or anything.
The basic idea of caching is to reuse previously used data to avoid time-consuming processing, and whatever data you want is fine.

Caching Objects and
I don't know how to use it differently when I use fragment cache.

fragment cache is a feature of rails that makes object caching convenient in views.

html generation is a time-consuming process, so I want to avoid it.
→ However, if you cache all the html, you can't handle pages that change part of it every time.
→ Then you can cache each part.But it's hard to write object cache every time.
→ Created a convenient mechanism for use
→ Let's call it fragment cache

It says (I think) around here.

Fragment caching is used for caching variable blocks without views without the entire action as a whole

Therefore, I think that the use of view is fragment cache, and the rest is object cache.
(Of course, you can use your own object cache, even if it's a view.)