Rails应用缓存问题：数据库数据已删除但Redis缓存仍存在

Hey there! The issue you're running into makes total sense—let's break it down and fix it quickly.

What's Going Wrong #

Your current after_save :clear_cache callback only triggers when a Snippet is created or updated. When you run @snippet.destroy, Rails doesn't fire the after_save hook—so your Redis cache key "snippets" never gets deleted, leaving stale data behind.

The Fix: Cover Delete Operations in Your Callbacks #

You have two solid options to make sure the cache gets cleared after deletions:

Option 1: Use after_commit (Recommended)

after_commit triggers after a database transaction is successfully committed, which covers create, update, AND destroy operations. This is more reliable than separate hooks because it avoids edge cases where a transaction might roll back but you've already cleared the cache.

Update your Snippet model like this:

class Snippet < ApplicationRecord
  # Trigger clear_cache after create, update, or destroy commits
  after_commit :clear_cache, on: [:create, :update, :destroy]

  def clear_cache
    $redis.del("snippets")
  end
end

Option 2: Add an after_destroy Hook

If you prefer to keep separate hooks, explicitly add after_destroy :clear_cache to cover deletion events:

class Snippet < ApplicationRecord
  after_save :clear_cache
  after_destroy :clear_cache

  def clear_cache
    $redis.del("snippets")
  end
end

Why This Works #

Now when you delete a Snippet, the clear_cache method will run, deleting the "snippets" key from Redis. The next time someone hits the index action, your fetch_snippets helper will detect the missing cache key, pull the latest data from the database, and repopulate the cache with the updated list.

Just a quick check: make sure your fetch_snippets helper logic correctly re-populates the cache when it's missing. It should look something like this (adjust if your implementation differs):

# In SnippetsHelper
def fetch_snippets
  cached_snippets = $redis.get("snippets")
  if cached_snippets
    JSON.parse(cached_snippets)
  else
    snippets = Snippet.all.to_a
    $redis.set("snippets", snippets.to_json)
    snippets
  end
end

That should resolve the inconsistency—your cache will now stay in sync with the database after deletes!

内容的提问来源于stack exchange，提问作者user3576036