$推送MongoDB中$ group中的过滤项

Question

我怎样才能推送$ group中的过滤记录？我需要做类似的事情：

db.products.aggregate(
    { $unwind: '$designs' },
    { $group: {
        _id: { '$_id' },
        data_1: { $push: {$designs: {$where: <condition1>}} },
        data_2: { $push: {$designs: {$where: <condition2>}} }
    }}
)