仅在mongodb集合中获取具有条件的第一个匹配文档

debugcn 发表于 Dev

莫希特·拉蒂（Mohit Rathi）

这是我的收藏

[
    {
        _id: "585be0da13385513689f704a",
        site: "NBT",
        url: "m.nbt.com",
        label: "NBT Home",
        platform: "mobile",
        speed: 61,
        date: "2016-12-22T14:18:57.975Z"
    },
    {
        _id: "585be0da13385513689f704b",
        site: "NBT",
        url: "nbt.com",
        label: "NBT Home",
        platform: "desktop",
        speed: 75,
        date: "2016-12-22T14:15:57.975Z"
    },
    {
        _id: "585be0da13385513689f704c",
        site: "MT",
        url: "m.mt.com",
        label: "MT Home",
        platform: "mobile",
        speed: 40,
        date: "2016-12-22T14:01:57.975Z"
    },
    {
        _id: "585be0da13385513689f704d",
        site: "NBT",
        url: "m.nbt.com",
        label: "NBT Home",
        platform: "mobile",
        speed: 90,
        date: "2016-12-22T12:18:57.975Z"
    }
]

预期产量：

[
    {
        _id: "585be0da13385513689f704b",
        site: "NBT",
        url: "nbt.com",
        label: "NBT Home",
        platform: "desktop",
        speed: 75,
        date: "2016-12-22T14:15:57.975Z"
    },
    {
        _id: "585be0da13385513689f704c",
        site: "MT",
        url: "m.mt.com",
        label: "MT Home",
        platform: "mobile",
        speed: 40,
        date: "2016-12-22T14:01:57.975Z"
    },
    {
        _id: "585be0da13385513689f704d",
        site: "NBT",
        url: "m.nbt.com",
        label: "NBT Home",
        platform: "mobile",
        speed: 90,
        date: "2016-12-22T12:18:57.975Z"
    }
]

基本上，我想先匹配不同的（标签+平台）组合文档。

如您所见，label- NBT Home存在于3个文档中，但是我只想检索label + platform的唯一组合。因此，我期望移动版NBT Home和桌面版NBT Home。

请帮忙。

费利克斯

试试这个：

db.collection.aggregate([
   {
      $group:{
         _id:{
            label:"$label",
            platform:"$platform"
         },
         site:{
            $first:"$site"
         },
         url:{
            $first:"$url"
         },
         speed:{
            $first:"$speed"
         }
      }
   }
])

输出：

{
    "_id" : {
        "label" : "MT Home",
        "platform" : "mobile"
    },
    "site" : "MT",
    "url" : "m.mt.com",
    "speed" : 40
}
{
    "_id" : {
        "label" : "NBT Home",
        "platform" : "desktop"
    },
    "site" : "NBT",
    "url" : "nbt.com",
    "speed" : 75
}
{
    "_id" : {
        "label" : "NBT Home",
        "platform" : "mobile"
    },
    "site" : "NBT",
    "url" : "m.nbt.com",
    "speed" : 61
}

本文收集自互联网，转载请注明来源。

如有侵权，请联系[email protected] 删除。