problem.sql

SELECT `problems`.* FROM `problems` LEFT OUTER JOIN `subject_nodes` ON `subject_nodes`.`id` = `problems`.`subject_node_id` WHERE `problems`.`deleted` = 0 AND (`problems`.`problem_subject_id` = 74 AND `problems`.`public` = 1 AND `problems`.`problem_set_type` IN (1, 2, 4) AND 'IF(problems.problem_set_type=4 AND problems.subject_node_id IS NOT NULL, subject_nodes.parent_id, problems.id) IS NOT NULL')

WHERE IF(problems.problem_set_type=4 AND problems.subject_node_id IS NOT NULL, subject_nodes.parent_id, problems.id) IS NOT NULL

WHERE IF(problems.problem_set_type=4 AND problems.subject_node_id IS NOT NULL, subject_nodes.parent_id IS NOT NULL, '')

WHERE (CASE problems.problem_set_type=4 AND problems.subject_node_id IS NOT NULL THEN subject_nodes.parent_id IS NOT NULL)

scope.rb

scope :public_problems_in_subject, lambda { |problem_subject_id|
  joins = arel_table.join(SubjectNode.arel_table, Arel::Nodes::OuterJoin).on(SubjectNode.arel_table[:id].eq(arel_table[:subject_node_id])).join_sources
  query = arel_table[:problem_subject_id].eq(problem_subject_id)
            .and(arel_table[:public].eq(true))
            .and(arel_table[:problem_set_type].in([PROBLEM_TYPE_QUIZ, PROBLEM_TYPE_DIAGNOSTIC, PROBLEM_TYPE_CONCEPT]))
            .and("(CASE problems.problem_set_type=#{PROBLEM_TYPE_CONCEPT} AND problems.subject_node_id IS NOT NULL THEN subject_nodes.parent_id IS NOT NULL END)")
  joins(joins).where(query)
}