mongo 更新数组 键值对

{ "_id" : 1, "grades" : [ 80, 85, 90 ] }{ "_id" : 2, "grades" : [ 88, 90, 92 ] }{ "_id" : 3, "grades" : [ 85, 100, 90 ] }

To update 80 to 82 in the grades array in the first document, use the positional $ operator if you do not know the position of the element in the array:

如果不知道值在数组的下标，可以用$操作把数组中的 80 更新成82

db.students.update(   { _id: 1, grades: 80 },   { $set: { "grades.$" : 82 } })

{  _id: 4,  grades: [     { grade: 80, mean: 75, std: 8 },     { grade: 85, mean: 90, std: 5 },     { grade: 90, mean: 85, std: 3 }  ]}
用$操作符 来更新 std 字段的内嵌文档
db.students.update(   { _id: 4, "grades.grade": 85 },   { $set: { "grades.$.std" : 6 } })