聚合包含嵌套文档的MongoDB数组

Question

我想让我的MongoDB数据库顾问:

我想做的是获取一些数据，这些数据集成在一个嵌套数组中，并通过这个嵌套键之一进行筛选。

文件内容如下:

[
{
"name": "PharmaMaria",
"country": "Spain",
"currency": "EUR",
"medicines": [
{
"name": "Medicine 1",
"type": "Suncream",
"price": 32,

},
{
"name": "Medicine 2",
"type": "Suncream",
"price": 5
},
{
"name": "Medicine 3",
"type": "Pills",
"price": 7
}
]
}
]

我想通过medicines.type

得到这样的结果

values = [
{
"name": "Medicine 1",
"price": 32
},
{
"name": "Medicine 2",
"price": 5
}
]

这是我创建的游乐场https://mongoplayground.net/p/_riatO8PKVp

谢谢!

Answer 1

您必须添加$project或$addFields阶段，并使用$filter运算符对每个元素应用条件。

db.collection.aggregate([
{
"$match": {
"country": "Spain",
"medicines.type": "Suncream"
},

},
{
"$addFields": {  // <- To add a new key
"medicines": {  // <- Replacing existing `medicines` key
"$filter": {  // <- Apply condition on each array elements
"input": "$medicines",
"as": "elem",
"cond": {  // <- Applying match condition inside this block
"$eq": [
"$$elem.type",
"Suncream"
],

}
}
}
}
},

])

使用$map

从数组中获取特定的键

db.collection.aggregate([
{
"$match": {
"country": "Spain",
"medicines.type": "Suncream"
},

},
{
"$addFields": {
"medicines": {
"$map": {
"input": {
"$filter": {
"input": "$medicines",
"as": "elem",
"cond": {
"$eq": [
"$$elem.type",
"Suncream"
],

}
}
},
"as": "med",
"in": {
"name": "$$med.name",
"price": "$$med.price",

}
},

}
}
},

])

上面的Mongo Execution示例

Mongo Playground Sample Execution