foreign_key_levels.rb

# Rails foreign key levels
table_names = (ActiveRecord::Base.connection.tables - %w[ar_internal_metadata schema_migrations])

$levels = table_names.map do |table_name|
  [table_name, 0]
end.to_h

$dependencies = table_names.map do |table_name|
  [table_name, []]
end.to_h

$links = table_names.map do |table_name|
  [table_name, []]
end.to_h

table_names.each do |table_name|
  foreign_keys = ActiveRecord::Base.connection.foreign_keys(table_name)
  foreign_keys.each do |foreign_key|
    $links[foreign_key.to_table] |= [foreign_key.from_table]
    $dependencies[foreign_key.from_table] |= [foreign_key.to_table]
  end
end

def update_levels(tables)
  tables.each do |parent_table|
    $links[parent_table].each do |child_table|
      $levels[child_table] = [$levels[parent_table] + 1, $levels[child_table]].max
    end
    update_levels($links[parent_table])
  end
end

root_tables = $dependencies.select { |table, dependencies| dependencies.size == 0 }.keys
update_levels(root_tables)

puts $levels