mongo根据数组长度查询
原文:https://www.itranslater.com/qa/details/2105880015459058688
https://stackoverflow.com/questions/7811163/query-for-documents-where-array-size-is-greater-than-1
({"ids":{"$exists":true, "$ne":[], "$not":{"$size":1}}}) ({$expr:{$gt:[{$size:"$ids"}, 1]}}) ({'ids.1': {$exists: true}})