我正在尝试获取文档内嵌套数组中键的平均数量，但不确定如何完成此操作。这是我的文档的样子:{"_id":{"$oid":"XXXXXXXXXXXXXXXXX"},"data":{"type":"PlayerRoundData","playerId":"XXXXXXXXXXXXX","groupId":"XXXXXXXXXXXXXX","holeScores":[{"type":"RoundHoleData","points":2},{"type":"RoundHoleData","points":13},{"type":"RoundHoleData","points":3},{"type