MongoDB的。从表中仅选择1列

Question

我有以下数据库

{"userName":"John Smith", "followers":8075,"body":"my text 1","confirmed":"no"}
{"userName":"james Bond", "followers":819, "body":"my text 2", "confirmed":"yes"}
{"userName":"Julia Roberts","followers":3882,"body":"my text 3","confirmed":"yes"}
{"userName":"Jamal David","followers":6531, "body":"my text 4","confirmed":"yes"}
{"userName":"jane fonda","followers":3941, "body":"my text 5","confirmed":"no"}

我需要计算名称以Ja开头的关注者数量（不区分大小写）

这就是我想要做的事情：

db.test.find({$and:[{followers:{$gte:0}}, {"userName":{$regex :/^Ja/i}}]})

但它给了我bach的整个匹配字符串，而我只需要userName。你能帮帮我吗？

Answer 1

将projection添加到查询

db.test.find({followers:{$gte:0}, userName:{$regex :/^Ja/i}}, {_id:0, userName:1})

请记住：

除非您在投影中指定_id:0，否则
• find始终返回_id。
• $和隐式使用操作 - 您不需要它来指定多个字段的过滤器