Wrong output for 3-way join

[neilconway]

Test case:

require "rubygems"
require "bud"

class CombosTestCase
  include Bud

  state do
    scratch :explicit_tc, [:from, :to]
    scratch :use_tiebreak, [:from, :to]
    scratch :sem_hist, [:from, :to]
    scratch :result, [:from, :to]
  end

  bloom do
    result <= (sem_hist * use_tiebreak * explicit_tc).combos(sem_hist.from => use_tiebreak.from, sem_hist.to => explicit_tc.from, sem_hist.from => explicit_tc.to) do |s,t,e|
      puts "JOIN RESULT: sem_hist: #{s}, use_tiebreak: #{t}, explicit_tc: #{e}"
      puts "sem_hist.from: #{s.from}; use_tiebreak.from: #{t.from}"
      [s.to, t.to]
    end
  end
end

c = CombosTestCase.new
c.explicit_tc <+ [[1, -Float::INFINITY]]
c.sem_hist <+ [[-Float::INFINITY, 1]]
c.use_tiebreak <+ [[1, 2]]
c.tick

puts c.result.to_a.sort.inspect

Expected results: empty array Observed results:

JOIN RESULT: sem_hist: [-Infinity, 1], use_tiebreak: [1, 2], explicit_tc: [1, -Infinity]
sem_hist.from: -Infinity; use_tiebreak.from: 1
[[1, 2]]

[neilconway]

Ah, interesting. The problem is the following:

1. The join predicates are given using the Ruby hash literal notation
2. The predicate names are method calls that return an array [tbl_name, column_offset, column_name]
3. Two join predicates have the same table name + column name on the LHS (e.g., sem_hist.from => x, sem_hist.from => y). This results in constructing a hash literal with two values for the same key, so Ruby just preserves the last key/value pair (sem_hist.from => y).

One kludgey way to fix the problem would be to have the schema accessors return an additional array element containing a unique ID (e.g., an incremented counter). If anyone has suggestions for a less gross fix, let me know...

[neilconway]

Another possible fix would be to rewrite the hash literal into an array literal in the rewriter. Not sure if that is more or less ugly, though...