ruby:jsonpath使用if case进行访问

我有一个下面的json。使用jsonpath gem，我可以通过

JsonPath.new("$.child_events[*]").on(b)

但是，我需要检查在child_事件中是否有“via_reference_id”

但这是行不通的。只有在任何子事件中存在“via\u引用\u id”时，我才能访问票证\u id

b = {"created_at"=>"2016-12-12T23:03:45Z", "ticket_id"=>24510, "timestamp"=>1481583825, "event_type"=>"Audit", "system"=>{"longitude"=>nil, "location"=>nil, "client"=>nil, "latitude"=>nil}, "id"=>110084880989, "updater_id"=>7964288149, "via"=>"Web form", "child_events"=>[{"event_type"=>"Change", "previous_value"=>"offered", "id"=>110084881029, "via_reference_id"=>nil, "satisfaction_score"=>"good", "via"=>"Web form"}, {"status"=>"open", "event_type"=>"Change", "via"=>"Rule", "id"=>110084881109, "via_reference_id"=>46315149, "rel"=>"trigger", "previous_value"=>"solved"}]}

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它以什么方式不起作用？@WayneConrad它抛出一个错误

SyntaxError:（eval）：1:语法错误，意外的']'

b = {"created_at"=>"2016-12-12T23:03:45Z", "ticket_id"=>24510, "timestamp"=>1481583825, "event_type"=>"Audit", "system"=>{"longitude"=>nil, "location"=>nil, "client"=>nil, "latitude"=>nil}, "id"=>110084880989, "updater_id"=>7964288149, "via"=>"Web form", "child_events"=>[{"event_type"=>"Change", "previous_value"=>"offered", "id"=>110084881029, "via_reference_id"=>nil, "satisfaction_score"=>"good", "via"=>"Web form"}, {"status"=>"open", "event_type"=>"Change", "via"=>"Rule", "id"=>110084881109, "via_reference_id"=>46315149, "rel"=>"trigger", "previous_value"=>"solved"}]}