聚合投影查询中出现无法识别的表达式错误

Question

无效的$project:：由：：无法识别的表达式'$$variantPricePoint.ppId'引起

{
"pricepoint": {
"$filter": {
"input": "$OriginalPricePoints",
"as": "varientPricePoint",
"cond": {
"$$varientPricePoint.ppId": {
"$in": ["PP100"]
}
}
}
},
"_id": 0
}

Answer 1

您不能将变量用作根对象键，而是需要使用$in运算符进行包装，如下所示：

{
"pricepoint": {
"$filter": {
"input": "$OriginalPricePoints",
"as": "varientPricePoint",
"cond": {
$in: [
"$$varientPricePoint.ppId",
["PP100"]
]
}
}
}
}