mongodb使用mongoose分组查询

一个分组查询的例子：

model.aggregate([{$match: ops}, {$unwind: \'$details\'}, {$sort: {create_at: -1}}, {
    $group: {
        _id: {
            promotion_id: "$promotion_id",
            product_id: \'$details.product_id\',
            need_pay: \'$need_pay\'
        },
        product_name: {$first:"$details.name"},
        price: {$max: "$details.price"},
        amount: {$sum: "$details.amount"},
        packing: {$sum: "$details.packing"},
        quantity: {$sum: "$details.quantity"}
    }
}, {$match: ops2}, {
    $group: {
        _id: {
            promotion_id: "$_id.promotion_id",
            need_pay: \'$_id.need_pay\'
        },
        details: {
            $push: {
                product_id: "$_id.product_id",
                name: \'$product_name\',
                price: \'$price\',
                amount: \'$amount\',
                packing: \'$packing\',
                quantity: \'$quantity\'
            }
        }
    }
}], fn);