db={"article_parent":[{"name":"name1","group":1},{"name":"name2","group":1},{"name":"name3","group":2},{"name":"name4","group":3},{"name":"name5","group":2}],"article":[{"parent_name":"name1","value":"val1"},{"parent_name":"name2","value":"val2"},{"parent_name":"name3","value":"val3"},{"parent_name":"name4","value":"val4"},{"parent_name":"name5","value":"val5"}]}

db.article.aggregate([{$lookup:{from:"article_parent",let:{pname:"$parent_name"},pipeline:[{$match:{$expr:{$eq:["$name","$$pname"]},group:2}}],as:"parent"}},{$match:{parent:{$ne:[]}}}])