本文介绍了简化MongoDB聚合的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在使用这种聚合按深度嵌套字段ObjectID对所有产品进行排序。
首先我填充CatalogProduct字段。
然后填充CatalogProduct内的类别。
按类别ID对所有数据排序(如果ID arr包含类别._id，则返回product)
按相反顺序排序，返回分页并按8限制分页。
然后获取没有分页和限制的所有已排序产品的总计数。
const sortedProducts = await StorageModel.aggregate([
// Unite products arr and totalCount of sorted products
{$facet: {
"sortedProducts": [
// populate catalogProduct ref by Id
{ $lookup: {
from: "catalogs",
localField: "catalogProduct",
foreignField: "_id",
as: "catalogProduct"
} },
// deconstruct this Arr, because we get only one Object
{ $unwind: "$catalogProduct" },
// populate category ref by Id inside catalogProduct object
{ $lookup: {
from: "categories",
localField: "catalogProduct.category",
foreignField: "_id",
as: "catalogProduct.category"
} },
// deconstruct this Arr, because we get only one Object
{ $unwind: "$catalogProduct.category" },
// returns product, if ids arr includes a catalogProduct.category._id
{ $match: {
"catalogProduct.category._id": { $in: ids }
} },
// sort in reverse order
{ $sort: { _id: -1 } },
// returns only *page
{ $skip: (page - 1) * 8 },
/// limit result by 8
{ $limit: 8 },
],
// total count for pagination, the same operations
"totalCount": [
{ $lookup: {
from: "catalogs",
localField: "catalogProduct",
foreignField: "_id",
as: "catalogProduct"
} },
{ $unwind: "$catalogProduct" },
{ $lookup: {
from: "categories",
localField: "catalogProduct.category",
foreignField: "_id",
as: "catalogProduct.category"
} },
{ $unwind: "$catalogProduct.category" },
{ $match: {
"catalogProduct.category._id": { $in: ids }
} },
// get total count of sorted data, without limit and pagination
{$count : "totalCount"},
]
}},
]);
products = sortedProducts[0].sortedProducts
totalProducts = sortedProducts[0].totalCount.totalCount我正在获取这样的数据：
[
{ sortedProducts: [ [Object], [Object] ], totalCount: [ [Object] ] }
]而且很好。但我认为，聚合可以简化，我不需要重复操作来获得总计数，但我不知道如何进行。
推荐答案
可以观察起始阶段，直到2中重复$matchbycatalogProduct.category._id。因此，您可以简单地将它们提取出来，然后将后续阶段分别放入$facet。
下面是我建议的代码版本：
StorageModel.aggregate([
{ $lookup: {
from: "catalogs",
localField: "catalogProduct",
foreignField: "_id",
as: "catalogProduct"
} },
// deconstruct this Arr, because we get only one Object
{ $unwind: "$catalogProduct" },
// populate category ref by Id inside catalogProduct object
{ $lookup: {
from: "categories",
localField: "catalogProduct.category",
foreignField: "_id",
as: "catalogProduct.category"
} },
// deconstruct this Arr, because we get only one Object
{ $unwind: "$catalogProduct.category" },
// returns product, if ids arr includes a catalogProduct.category._id
{ $match: {
"catalogProduct.category._id": { $in: ids }
} },
// Unite products arr and totalCount of sorted products
{$facet: {
"sortedProducts": [
// populate catalogProduct ref by Id
// sort in reverse order
{ $sort: { _id: -1 } },
// returns only *page
{ $skip: (page - 1) * 8 },
/// limit result by 8
{ $limit: 8 },
],
// total count for pagination, the same operations
"totalCount": [
// get total count of sorted data, without limit and pagination
{$count : "totalCount"},
]
}},
]);
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