$ lookup结果使用另一个数组中的键排序

安妮塔·保罗

我有以下数据结构：

播放列表集合：

{
    _id:123,
    artistId:959789,
    title:'playlist1',
    tracks:[{trackId:123456,createdDate:03.02.2017},
        {trackId:213556,createdDate:04.02.2017},
        {trackId:956125,createdDate:05.02.2017}]
},
{
    _id:456,
    artistId:456456,
    title:'playlist2',
    tracks:[{trackId:956336,createdDate:03.02.2017},
        {trackId:213556,createdDate:09.02.2017},
        {trackId:785556,createdDate:011.02.2017}]
},
{
    _id:456,
    artistId:456456,
    title:'playlist3',
    tracks:[{trackId:636985,createdDate:01.02.2017},
        {trackId:456585,createdDate:06.02.2017},
        {trackId:785556,createdDate:09.02.2017}]
}

所述trackId播放列表的曲目阵列中是_id一个轨道的轨道集合中

曲目收集：

{_id:956336,title:'abc'},
{_id:785556,title:'cdf'},
{_id:456585,title:'ghi'},
{_id:213556,title:'xyz'},
{_id:636985,title:'lmn'}

我所做的是在数组中$lookup使用的聚合trackId，tracks并且得到了结果。但是playlistTracks是以其他某种顺序排序的，而不是以tracks数组顺序的顺序排序。

{
        $match: {artistId: 456}
},
{
    $lookup: {
            from: 'tracks',
            localField: 'tracks.trackId',
            foreignField: '_id',
            as: 'playlistTracks'
        }
},

现在我需要的是让具有下列结构的特定艺术家播放列表的列表：本playlistTracks应在上的顺序排序createdDate中tracks数组。

{
    _id:456,
    title:'playlist2',
    tracks:[{trackId:636985,createdDate:01.02.2017},
        {trackId:456585,createdDate:06.02.2017},
        {trackId:785556,createdDate:09.02.2017}]
    playlistTracks:[{_id:956336,title:'abc'},
            {_id:213556,title:'xyz'},
            {_id:785556,title:'cdf'}]
},
{
    _id:456,
    title:'playlist2',
    tracks:[{trackId:636985,createdDate:01.02.2017},
        {trackId:456585,createdDate:06.02.2017},
        {trackId:785556,createdDate:09.02.2017}]
    playlistTracks:[{_id:636985,title:'lmn'},
            {_id:456585,title:'ghi'},
            {_id:785556,title:'cdf'}]
}

M14

遵循以下步骤

1 unwind the tracks array in playlist collection
2 $lookup match with tracks collection
3 add createddate of tracks array to lookup result as a new key
4 sort based on new key
5 group the results for your requirements

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