MongoDB聚合$或与$ elemMatch一起使用，在$ lookup管道中包含$ expr [英] MongoDB aggregation $or with $elemMatch, $expr inside $lookup pipeline

问题描述

我有2个收藏集:

用户集合:

{
    _id: ObjectId
}

多多收藏集:

{
    _id: ObjectId
    fieldA: {_id: ObjectId}
    fieldB: [{_id: ObjectId}, {_id: ObjectId}]
}

并且我正在尝试加入 fieldA的ID 或 fieldB的ID 之一与用户的ID 匹配的A集合的元素以下聚合:

And I'm trying to join the element of A collection which fieldA's id OR one of fieldB's id is matching with user's id with following aggregation :

db.users.aggregate([
{
  $lookup: {
    from: "Toto",
    let: { "user_id": "$_id" },
    as: "fcollection",
    pipeline: [
      { $match:  
        {$or:[
          {"fieldB": {$elemMatch: {"_id": "$$user_id"}}}, 
          {$expr: {$eq :["$fieldA._id", "$$user_id"]}}
        ]}
      }
    ]
  }
])

但是在输出中，我只是获取文档，其中fieldA的ID匹配，但没有fieldB的ID.我在做什么错了?

But in the output I'm just getting the document's where fieldA's id is matching but none of the fieldB's. What am I doing wrong?

推荐答案

您需要使用 $ in 聚合管道运算符，用于检查数组中是否存在元素:

You need to use $in aggregation pipeline operator to check an element exists in an array :

db.users.aggregate([
  {
    $lookup: {
      from: "Toto",
      let: {
        "user_id": "$_id"
      },
      as: "fcollection",
      pipeline: [
        {
          $match: {
            $or: [
              {
                $expr: {
                  $in: [
                    "$$user_id",
                    "$fieldB._id"
                  ]
                }
              },
              {
                $expr: {
                  $eq: [
                    "$fieldA._id",
                    "$$user_id"
                  ]
                }
              }
            ]
          }
        }
      ]
    }
  }
])

测试: MongoDB-Playground

这篇关于MongoDB聚合$或与$ elemMatch一起使用，在$ lookup管道中包含$ expr的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！