instance method collapse_wheres

# File activerecord/lib/active_record/relation/query_methods.rb, line 199
    def collapse_wheres(arel, wheres)
      equalities = wheres.grep(Arel::Nodes::Equality)

      groups = equalities.group_by do |equality|
        equality.left
      end

      groups.each do |_, eqls|
        test = eqls.inject(eqls.shift) do |memo, expr|
          memo.and(expr)
        end
        arel = arel.where(test)
      end

      (wheres - equalities).each do |where|
        where = Arel.sql(where) if String === where
        arel = arel.where(Arel::Nodes::Grouping.new(where))
      end
      arel
    end