id_match.rb

Issue = Struct.new(:id, :name)
Note = Struct.new(:id, :issue_id, :name)

issue1 = Issue.new(1, "aaa")
issue2 = Issue.new(2, "bbb")

note1_1 = Note.new(1, 1, "note1-1")
note1_2 = Note.new(2, 1, "note1-2")
note2_1 = Note.new(3, 2, "note2-1")

issues = [issue1, issue2]
notes = [note1_1, note1_2, note2_1]

p notes.select { |n| n.issue_id == issue1.id }  # => [#<struct Note id=1, issue_id=1, name="note1-1">, #<struct Note id=2, issue_id=1, name="note1-2">]
p notes.select { |n| n.issue_id == issue2.id }  # => [#<struct Note id=3, issue_id=2, name="note2-1">]