Class: Publication::MostRecentRevisionLookup

Inherits:
Object
  • Object
show all
Defined in:
app/services/publication/most_recent_revision_lookup.rb

Overview

Service to efficiently precompute most recent revisions for a collection of publications.
This avoids N+1 queries by computing all revisions in a single database query.

Usage:
lookup = Publication::MostRecentRevisionLookup.new(publications)
most_recent_revisions = lookup.lookup_hash
most_recent = most_recent_revisions[publication.id]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(publications) ⇒ MostRecentRevisionLookup

Returns a new instance of MostRecentRevisionLookup.



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# File 'app/services/publication/most_recent_revision_lookup.rb', line 14

def initialize(publications)
  @publications = publications
end

Instance Attribute Details

#publications ⇒ Object (readonly)

Returns the value of attribute publications.



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# File 'app/services/publication/most_recent_revision_lookup.rb', line 12

def publications
  @publications
end

Instance Method Details

#lookup_hash ⇒ Object

Returns a hash mapping publication ID -> most recent revision (Item object)
If the publication IS the most recent revision, the value will be nil to indicate "no newer revision"



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# File 'app/services/publication/most_recent_revision_lookup.rb', line 20

def lookup_hash
  return {} if publications.blank?

  # Extract canonical SKUs from the current publications
  publication_ids = publications.map(&:id)
  canonical_skus_map = publications.to_h { |pub| [pub.id, extract_canonical_sku(pub.sku)] }

  # Get unique canonical SKUs
  unique_canonical_skus = canonical_skus_map.values.uniq

  # Build a single query to find the most recent revision for each canonical SKU
  # Using a subquery with DISTINCT ON for efficiency
  most_recent_by_canonical = find_most_recent_revisions(unique_canonical_skus)

  # Build the lookup hash
  result = {}
  publications.each do |pub|
    canonical_sku = canonical_skus_map[pub.id]
    most_recent = most_recent_by_canonical[canonical_sku]

    # Only return a value if there's a different, newer revision
    result[pub.id] = most_recent if most_recent && most_recent.id != pub.id
  end

  result
end