code: def build_multi_selection_condition(hashes, keys = unique_index_keys)
        arel_table = model_class.arel_table
        # We do pure SQL OR, since Arel is nesting every .or into another parentheses, otherwise this would be just
        # inject(:or) instead of to_sql with .join(" OR ")
        hashes.map { |hash| "(#{keys.map { |key| arel_table[key].eq(hash[key]) }.inject(:and).to_sql})" }.join(" OR ")
      end
docs: Builds a multiselection conditions like (table1.a = a1 AND table2.b = b1) OR (table1.a = a2 AND table2.b = b2)
  
   @param hashes [Array<Hash>] data we want to use for the query
   @param keys [Array<Symbol>] keys of attributes involved
   @return [String] A condition usable in .where of an ActiveRecord relation