MongoDB $project: $filter子数组

Question

MongoDB $project: $filter子数组

11

有一个物品（mongoose）模式，看起来像这样（简化到问题所在的部分）：

{
    brand: {
        name: String,
    },
    title: String,
    description: [{ lang: String, text: String }],
    shortDescription: [{ lang: String, text: String }],
    variants: {
        cnt: Number,
        attrs: [
            {
                displayType: String,
                displayContent: String,
                displayName: [{ lang: String, text: String }],
                name: String,
            },
        ],
    }
}

我正在尝试通过语言筛选项目，因此我构建了以下查询：

db.items.aggregate([
    { $match: { 'description.lang': 'ca', 'shortDescription.lang': 'ca' } },
    { $project: {
        'brand.name': 1,
        title: 1,
        description: {
            '$filter': {
                input: '$description',
                as: 'description',
                cond: { $eq: ['$$description.lang', 'ca'] }
            }
        },
        shortDescription: {
            '$filter': {
                input: '$shortDescription',
                as: 'shortDescription',
                cond: { $eq: ['$$shortDescription.lang', 'ca'] }
            }
        },
        'variants.cnt': 1,
        'variants.attrs': 1
    } }
])

它按预期工作：通过语言过滤description和shortDescription。我现在想知道是否也可以过滤每个variants.attrs.$.displayName。有什么方法可以做到吗？

我一直在尝试使用$unwindvariant.attrs，但是当我尝试再次$group时完全迷失了方向，我不确定这是否是最佳方法...

- Miquel

我有一个问题：description、shortDescription、variants.attrs和variants.attrs.displayName都是列表。这4个列表都可以有多个元素吗？ - sergiuz

是的，它们包含每种语言的文本。 description: [{ lang:'en', text: 'This item is awful' }, { lang: 'es', text: 'Este producto es increíble' }, ...] - Miquel

1个回答

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- Nishant Bhardwaj · Accepted Answer

你快要成功了。请尝试以下步骤：

use $unwind stage before $project stage to expand the outer array of documents, i.e. variants.attrs
Add filter for the sub array variants.attrs.displayName in the $project stage.
You will have to project all the sub fields of variants key.
Next add $group stage and group by all the elements except the sub-array. Use $push to rebuild the sub array in group by stage.

Lastly, add $project stage to rebuild the document to its original structure.

db.items.aggregate([
  { $match: { 'description.lang': 'ca', 'shortDescription.lang': 'ca' } },
  { $unwind : "$variants.attrs" },
  { $project: {
     '_id' : 1,
     'brand.name': 1,
     title: 1,
     description: {
        '$filter': {
            input: '$description',
            as: 'description',
            cond: { $eq: ['$$description.lang', 'ca'] }
        }
     },
     shortDescription: {
       '$filter': {
           input: '$shortDescription',
           as: 'shortDescription',
           cond: { $eq: ['$$shortDescription.lang', 'ca'] }
        }
     },
     'variants.attrs.displayName' : {
        '$filter' : {
           input: '$variants.attrs.displayName',
           as: 'variants_attrs_displayName',
           cond: { $eq : ['$$variants_attrs_displayName.lang','ca']}
        }
      },

      'variants.cnt': 1,
      'variants.attrs.displayType': 1,
      'variants.attrs.displayContent' : 1,
      'variants.attrs.name' : 1
    } 
 } , { $group:
          {
            _id : { 
                _id: "$_id",
                title: "$title",
                brand:"$brand",
                description:"$description",
                shortDescription:"$shortDescription", 
                variants_cnt : "$variants.cnt"
                },
            variants_attrs : { $push : 
            { 
              displayType : "$variants.attrs.displayType",
              displayContent : "$variants.attrs.displayContent",
              displayName : "$variants.attrs.displayName",
              name: "$variants.attrs.name" 
            }
          }
        }
    },
{ $project : 
 {
    "_id" : 0,
    brand : "$_id.brand",
    title : "$_id.title",
    description : "$_id.description",
    shortDescription : "$_id.shortDescription",
    variants : {
      cnt : "$_id.variants_cnt" ,
      attrs : "$variants_attrs"
     }
   }  
 }
])

根据您的使用情况，您应重新考虑数据模型设计，以避免过滤值的重复。即：'description.lang': 'ca', 'shortDescription.lang': 'ca', 'variants.attrs.displayName.lang': 'ca'。