mongdb怎么在查找的时候统计某列数据

Question

假设有文档：

[
 { name: 'a', content: 'xxx', list: [ 'A', 'A', 'C' ] },
 { name: 'b', content: 'yyy' ,list: [ 'A', 'B' ] },
 { name: 'c', content: 'zzz', list: [ 'B' ] }
]

期望统计 list 中 A 元素个数，并保持其他信息字段不变：

[
 { name: 'a', content: 'xxx', list: 2 },
 { name: 'b', content: 'yyy' ,list: 1 },
 { name: 'c', content: 'zzz', list: 0 }
]

请问在 mongodb 要怎么写查询语句？

Answer 1

https://blog.csdn.net/qq_42938842/article/details/84592353