我正在尝试使用聚合框架展平嵌套数组,但无法获得结果。 我的收藏是:
[
{
"id" : "xxx",
"countryName" : "xxx",
"cities" : [
{
"id" : "xxx",
"cityName" : "xxx"
},
{
"id" : "xxx",
"cityName" : "xxx"
}
]
}
]
我想从所有国家获得城市,我想要的结果是:
[
{
"id" : "xxx",
"cityName" : "xxx"
},
{
"id" : "xxx",
"cityName" : "xxx"
}
]
我尝试了此请求:
val aggregation = Aggregation.newAggregation(
Aggregation.group("cities")
)
return mongoDb.aggregate(aggregation, Country::class.java, Any::class.java).mappedResults
但是,我得到了这个结果:
[
{
"_id": [
{
"id": "xxx",
"cityName": "xxx"
},
{
"id": "xxx",
"cityName": "xxx"
}
]
}
]
有人可以帮我吗?
答案 0 :(得分:0)
此聚合将帮助您实现结果,但必须使用Java
驱动程序对其进行调整:
db.countries.aggregate([
{
"$unwind": "$cities"
},
{
"$project": {
"_id": 0,
"cities": 1
}
},
{
"$replaceRoot": {
"newRoot": "$cities"
}
}
])