这里是订单和产品的一个假设案例。
- "产品"系列
[
{
"_id": "61c53eb76eb2dc65de621bd0",
"name": "Product 1",
"price": 80
},
{
"_id": "61c53efca0a306c3f1160754",
"name": "Product 2",
"price": 10
},
... // truncated
]
- '订单'集合:
[
{
"_id": "61c53fb7dca0579de038cea8", // order id
"products": [
{
"_id": "61c53eb76eb2dc65de621bd0", // references products._id
"quantity": 1
},
{
"_id": "61c53efca0a306c3f1160754",
"quantity": 2
},
]
}
]
正如您所看到的,订单拥有一个产品ID列表。当我提取订单的详细信息时,我还需要产品详细信息的组合,比如:
{
_id: ObjectId("61c53fb7dca0579de038cea8"),
products: [
{
_id: ObjectId("61c53eb76eb2dc65de621bd0"),
quantity: 1,
name: 'Product 1',
price: 80
},
{
_id: ObjectId("61c53efca0a306c3f1160754"),
quantity: 2,
name: 'Product 2',
price: 10
},
... // truncated
]
}
这是我提出的聚合流水线:
db.orders.aggregate([
{
$match: {_id: ObjectId('61c53fb7dca0579de038cea8')}
},
{
$unwind: {
path: "$products"
}
},
{
$lookup: {
from: 'products',
localField: 'products._id',
foreignField: '_id',
as: 'productDetail'
}
},
{
$unwind: {
path: "$productDetail"
}
},
{
$group: {
_id: "$_id",
products: {
$push: {$mergeObjects: ["$products", "$productDetail"]}
}
}
}
])
考虑到数据的组织方式,我怀疑管道阶段是否是最佳的,是否可以做得更好(减少阶段数量的可能性等(。有什么建议吗?
正如评论中已经提到的,设计很差。您可以避免多个$unwind
和$group
,通常情况下,的性能会更好
db.orders.aggregate([
{ $match: { _id: "61c53fb7dca0579de038cea8" } },
{
$lookup: {
from: "products",
localField: "products._id",
foreignField: "_id",
as: "productDetail"
}
},
{
$project: {
products: {
$map: {
input: "$products",
as: "product",
in: {
$mergeObjects: [
"$$product",
{
$first: {
$filter: {
input: "$productDetail",
cond: { $eq: [ "$$this._id", "$$product._id" ] }
}
}
}
]
}
}
}
}
}
])
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