我嘗試使用mongodb官方檔案中的一個例子，
db.students3.updateMany({ },
[
{ $set: { grade: { $switch: {
branches: [
{ case: { $gte: [ "$average", 90 ] }, then: "A" },
{ case: { $gte: [ "$average", 80 ] }, then: "B" },
{ case: { $gte: [ "$average", 70 ] }, then: "C" },
{ case: { $gte: [ "$average", 60 ] }, then: "D" }
],
default: "F"
} } } }
])
屬性grade被定義為Number型別。當我嘗試更新資料庫 student3 中的所有檔案時出現錯誤，
CastError: Cast to Number failed for value "{ '$switch': { branches: [ [Object] ] } }" (type Object) at path "grade"
有人可以解釋這個錯誤嗎？謝謝。
uj5u.com熱心網友回復：
你必須$trunc首先，然后average欄位將被創建。
{ $set: { average : { $trunc: [ { $avg: "$tests" }, 0 ] }, modified: "$$NOW" } }
完整更新
db.collection.update({},
[
{
$set: {
average: { $trunc: [ { $avg: "$tests" }, 0 ] },
modified: "$$NOW"
}
},
{
$set: {
grade: {
$switch: {
branches: [
{ case: { $gte: [ "$average", 90 ] }, then: "A" },
{ case: { $gte: [ "$average", 80 ] }, then: "B" },
{ case: { $gte: [ "$average", 70 ] }, then: "C" },
{ case: { $gte: [ "$average", 60 ] }, then: "D" }
],
default: "F"
}
}
}
}
])
mongoplayground
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