Fix Read-Only Errors for Cache Deletion in MultiDB Setup with database_selector

[Dandush03]

Description

When using Rails' MultiDB configuration with database_selector, attempts to delete entries from the SolidCache::Entry model may result in a read-only error. This issue arises because the database_selector configuration causes certain operations to route to the replica database, which is read-only.

The Error

The following error occurs when the application tries to execute a DELETE query in a replica marked as read-only by rails middleware

ActionView::Template::Error (Write query attempted while in readonly mode: DELETE FROM "solid_cache_entries" WHERE "solid_cache_entries"."key_hash" = 8850981528477303422)

This error disrupts operations that rely on cache clearing, such as session management or dynamic cache updates.

Reproduction Steps

1. Add the following configuration to your Rails app:

Rails.application.configure do
  config.active_record.database_selector = { delay: 2.seconds }
  config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
  config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
end

2. Configure a primary and replica database in database.yml.

3. Attempt to delete a cache entry using SolidCache::Entry in a context where the replica database connection is active.
   Observe the error described above.

Hint: I suggest using devise user_sign_in? method in an index action since it would make it easier to reproduce

Expected Behavior

Cache-related models like SolidCache::Entry should always use the writable primary database for operations that require modifications, regardless of the database_selector configuration.

My current solution:

# config/initializer/override_read_only_for_cache.rb
module OverrideReadOnlyForCache
  def readonly?
    false
  end
end

Rails.application.config.after_initialize do
  SolidCache::Entry.prepend(OverrideReadOnlyForCache)
end

This ensures that the model is always writable, bypassing the default read-only behavior in a MultiDB setup.

[ausangshukla]

Same MultiDB setup. This fix is not working for me, I get the error

ActiveRecord::ReadOnlyError - Write query attempted while in readonly mode: INSERT INTO solid_cache_entries
solid_cache (1.0.6)

Note there is no error with solid_cache (1.0.2), however the cache is not being populated, ie
mysql> select * from solid_cache_entries;
Empty set (0.00 sec)

Please can you help

[Dandush03]

Sorry for the delay, this should do the trick

module OverrideReadOnlyForCache
  # Instance method overrides
  def save(...)
    run_in_writing_role { super(...) }
  end

  def save!(...)
    run_in_writing_role { super(...) }
  end

  def create(...)
    run_in_writing_role { super(...) }
  end

  def create!(...)
    run_in_writing_role { super(...) }
  end

  def destroy(...)
    run_in_writing_role { super(...) }
  end

  def destroy!(...)
    run_in_writing_role { super(...) }
  end

  def destroy_all(...)
    run_in_writing_role { super(...) }
  end

  def delete(...)
    run_in_writing_role { super(...) }
  end

  def delete_all(...)
    run_in_writing_role { super(...) }
  end

  def update(...)
    run_in_writing_role { super(...) }
  end

  def update!(...)
    run_in_writing_role { super(...) }
  end

  def update_all(...)
    run_in_writing_role { super(...) }
  end

  def upsert_all(...)
    run_in_writing_role { super(...) }
  end

  def update_attribute(...)
    run_in_writing_role { super(...) }
  end

  def update_columns(...)
    run_in_writing_role { super(...) }
  end

  def touch(...)
    run_in_writing_role { super(...) }
  end

  def increment(...)
    run_in_writing_role { super(...) }
  end

  def increment!(...)
    run_in_writing_role { super(...) }
  end

  def decrement(...)
    run_in_writing_role { super(...) }
  end

  def decrement!(...)
    run_in_writing_role { super(...) }
  end

  def update_counters(...)
    run_in_writing_role { super(...) }
  end

  def self.prepended(base)
    base.singleton_class.prepend(ClassMethods)
  end

  module ClassMethods
    def save(...)
      run_in_writing_role { super(...) }
    end

    def save!(...)
      run_in_writing_role { super(...) }
    end

    def create(...)
      run_in_writing_role { super(...) }
    end

    def create!(...)
      run_in_writing_role { super(...) }
    end

    def destroy(...)
      run_in_writing_role { super(...) }
    end

    def destroy!(...)
      run_in_writing_role { super(...) }
    end

    def destroy_all(...)
      run_in_writing_role { super(...) }
    end

    def delete(...)
      run_in_writing_role { super(...) }
    end

    def delete_all(...)
      run_in_writing_role { super(...) }
    end

    def update(...)
      run_in_writing_role { super(...) }
    end

    def update!(...)
      run_in_writing_role { super(...) }
    end

    def update_all(...)
      run_in_writing_role { super(...) }
    end

    def upsert_all(...)
      run_in_writing_role { super(...) }
    end

    def update_attribute(...)
      run_in_writing_role { super(...) }
    end

    def update_columns(...)
      run_in_writing_role { super(...) }
    end

    def touch(...)
      run_in_writing_role { super(...) }
    end

    def increment(...)
      run_in_writing_role { super(...) }
    end

    def increment!(...)
      run_in_writing_role { super(...) }
    end

    def decrement(...)
      run_in_writing_role { super(...) }
    end

    def decrement!(...)
      run_in_writing_role { super(...) }
    end

    def update_counters(...)
      run_in_writing_role { super(...) }
    end

    private

    def run_in_writing_role(&)
      ActiveRecord::Base.connected_to(role: :writing, &)
    end
  end

  private

  def run_in_writing_role(&)
    ActiveRecord::Base.connected_to(role: :writing, &)
  end
end

Rails.application.config.to_prepare do
  SolidCache::Entry.prepend(OverrideReadOnlyForCache) unless Rails.env.test?
end

[djmb]

@Dandush03, @ausangshukla - what do your config/[solid_]cache.yml and config/database.yml look like?