MongoDB -复制字段到另一个集合

Question

假设我有一个collectionorders:

[
{
"id":"1",
"items":{
"itemId":"1000",
"name":"Item 1",
"status":"STATUS"
}
},
{
"id":"2",
"items":{
"itemId":"1000",
"name":"Item 1",
"status":"ANOTHER_STATUS"
}
}
]

我有另一个集合item_projections它是

[
{
"id":"1",
"itemId":"1000",
"name":"Item 1",
"orderId":"1"
},
{
"id":"1",
"itemId":"1000",
"name":"Item 1",
"orderId":"2"
}
]

对于集合orders中的每个项目，我想将字段status复制到投影中，并匹配顺序id和itemId，以具有

[
{
"id":"1",
"itemId":"1000",
"name":"Item 1",
"orderId":"1",
"status":"STATUS"
},
{
"id":"1",
"itemId":"1000",
"name":"Item 1",
"orderId":"2",
"status":"ANOTHER_STATUS"
}
]

有可能用聚合查找和合并管道来做吗?

Answer 1

解决方案1

1. $lookup-item_projectionscollection (key:orderId)连接orderscollection (key:id)，返回orders数组字段，仅包含status字段的文档。

2. $replaceRoot-用新文档替换输入文档。

   2.1。$mergeObjects-将根文档与orders的第一个文档合并。

3. $unset-删除orders字段。

db.item_projections.aggregate([
{
"$lookup": {
"from": "orders",
"localField": "orderId",
"foreignField": "id",
"pipeline": [
{
$project: {
status: "$items.status"
}
}
],
"as": "orders"
}
},
{
$replaceRoot: {
newRoot: {
$mergeObjects: [
"$$ROOT",
{
$first: "$orders"
}
]
}
}
},
{
$unset: "orders"
}
])

Sample Mongo Playground (Solution 1)

---

解决方案2

或者你可以用$project代替第二和第三级。

{
$project: {
"id": 1,
"itemId": 1,
"name": 1,
"orderId": 1,
"status": {
$first: "$orders.status"
}
}
}

Sample Mongo Playground (Solution 2)