mongoDB中要填充的聚合问题

thtygnil 于 2023-05-06 发布在 Go

关注(0)|答案(1)|浏览(134)

事务模型中有许多信息是不需要的，例如，我们不知道事务是注册为经销商还是交付，如果是注册为经销商还是交付，则另一个为空

dealer: {
  type: SchemaTypes.ObjectId,
  ref: 'Dealer',
  required: false,
},
delivery: {
  type: SchemaTypes.ObjectId,
  ref: 'Delivery',
  required: false,
},

当我使用aggregate时，只返回同时具有dealer值和delivery的数据

const aggregate = [
{
  $lookup: {
    from: 'deliveries',
    localField: 'delivery',
    foreignField: '_id',
    as: 'delivery',
  },
},
 {
  $unwind:"$delivery",
  },
{
  $lookup: {
    from: 'dealers',
    localField: 'dealer',
    foreignField: '_id',
    as: 'dealer',
  },
},
{
  $unwind: '$dealer',
}]

因此，不返回任何数据如何进行聚合如果文档中有字段，则不存在也无所谓

mongodb

来源：https://stackoverflow.com/questions/76172701/problem-with-aggregate-in-mongodb-to-populate

1条答案

按热度按时间

cgh8pdjw1#

你可以将$unwind设置为true，这样如果有一个空数组要展开，文档就不会被删除。这是一个mongoplayground demo

const aggregate = [
  {
    $lookup: {
      from: "deliveries",
      localField: "delivery",
      foreignField: "_id",
      as: "delivery",
      
    }
  },
  {
    $unwind: {
      path: "$delivery",
      preserveNullAndEmptyArrays: true
    }
  },
  {
    $lookup: {
      from: "dealers",
      localField: "dealer",
      foreignField: "_id",
      as: "dealer",
      
    }
  },
  {
    $unwind: {
      path: "$dealer",
      preserveNullAndEmptyArrays: true
    }
  }
]

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mongoDB中要填充的聚合问题

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