简化MongoDB聚合

Question

I'm using such aggregation to sort all products by deep nested field ObjectId.

At first I populate catalogProduct field.

Then populate category inside catalogProduct.

Sort all data by category Id (return product if ids arr includes category._id)

Sort in reverse order, returns page and limit by 8 for pagination.

Then getting total count of all sorted products without paginatin and limit.

 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

I'm getting such data:

 [ { sortedProducts: [ [Object], [Object] ], totalCount: [ [Object] ] } ]

And It's fine. But I think, that aggregation can be simplified, and i don't need to repeat operations to get total count, but I don't know how.

Answer 1

You can observe the starting stages until $match by catalogProduct.category._id is repeated in the 2 $facet . Therefore, you can simply factor them out, then put the afterwards stages into $facet respectively.

Below is my suggested version of your code:

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"},
        ]
        }},
]);