ActiveRecord::PreparedStatementCacheExpired errors due to document after save hook

[jsugarman]

How to replicate
Deployment of the application which includes a migration against the documents table (Document model) coupled with saving a claim (on a server instance that has not been restarted since the migration?!)

Impact
Will raise an ActiveRecord::PreparedStatementCacheExpired error and users creating or updating claims
will experience a 500 error and possibly lose some changes they have made as a result.

Cause
The code below means that any save on claim queries and could attempt to update the document table. I believe the query itself is what can raise the error. If the document table has been migrated the query's prepared statement expires. Existing sessions on a server that have not been restarted following the migration will therefore be using an expired statement?!

    # app/models/claim/base_claim.rb
    after_save :find_and_associate_documents, :update_vat
    ...
    ...
    def find_and_associate_documents
      return if form_id.nil?

      Document.where(form_id: form_id).find_each do |document| <---- this line raises error
        document.update_column(:claim_id, id)
        document.update_column(:external_user_id, external_user_id)
      end
    end

Fix

This article is useful background reading but we should question whether we even need this after_save hook now.

[jrmhaig]

Further to the comment about whether we need the after_save block, it is possible that we can set the claim_id and external_user_id fields when the document is uploaded rather than when the claim is submitted.