fix cache bug

[BenZhang]

Hi, I ran into a very strange situation.

json.array! [1,2,3] do |i|
  json.cache! 'test' do
    json.name 'cache'
  end
  json.id i
end

The code above will print

[
  {"name":"cache","id":1},
  {"name":"cache","id":3},
  {"name":"cache","id":3}
]

If we move json.id on the top, it will work. The reason for that is when use cache! in the beginning of the block it will retrieve the same cached object from previous iteration and overwrite it. I think it is the same reason for this issue #330

[rails-bot]

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[BenZhang]

After further investigation, this will only happen when using memory_store for the cache. It is actually caused by the behaviour of Rails cache. Please see below example

Rails.cache.write('user', {id: 1})
a = Rails.cache.read('user')
#=> {:id=>1}
a[:name] = "Hello"
Rails.cache.read('user')
#=> {:id=>1, :name => "Hello"}

[ryanb]

I ran into this today. It would be great to get it fixed! Can someone address this PR?

[EvTi]

One more bug, i think

json.cache_collection! [1,2,3] do |category|
  next
end

result

{}
{}
{}

[dhh]

I know this is a million years old, but just stumbled over it. It strikes me as odd this is only happening in the memory store. That implies to me it should be fixed in the memory store. Anyone interested in digging deeper?

[pixeltrix]

@dhh what version was this in? I've tried using @BenZhang's test and his cache commands and can't seem to reproduce in any version of 7.x

Looking at his sequence of commands suggests it's an example of rails/rails#36956:

Rails.cache.write('user', {id: 1})
a = Rails.cache.read('user')
#=> {:id=>1}
a[:name] = "Hello"
Rails.cache.read('user')
#=> {:id=>1, :name => "Hello"}

that's not been applicable since rails/rails#37210.

[dhh]

Ha. Makes sense. The initial report was ancient but hadn't seen any updates. Will close. Thanks @pixeltrix 🙏