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mongodbpipeline

mongodb pipeline limit to 1

I am trying to limit the returning array to just 1, currently when I run this it shows me all the results under the added season How do I limit the season to return 1.

{
  'from': 'episode',
  'let': {
    'episodeId': '$_id'
  },
  'pipeline': [{
    "$match": {
      "$expr": {
        "$eq": ["$show_id", "$$episodeId"]
      }
    }
  }, {
      "$sort": {
        "pubDate": -1
      }
  
    
    
    
  }],
  'as': 'season'
}

Basically all I need from the sub-array is the first season number in the picture below you can see it is season 3.

season query

when I add the limit to the pipeline I get "Stage must be a properly formatted document."

enter image description here

Solution

  • Try this,

    db.show.aggregate([
  {
    "$lookup": {
      "from": "episode",
      "let": {
        "episodeId": "$_id"
      },
      "pipeline": [
        {
          "$match": {
            "$expr": {
              "$eq": [
                "$show_id",
                "$$episodeId"
              ]
            }
          }
        },
        {
          "$sort": {
            "pubDate": -1
          }
        },
        {
          $limit: 1
        }
      ],
      "as": "season"
    }
  }
])

    You would get the out put as

    [
  {
    "_id": 1,
    "season": [
      {
        "_id": 2,
        "pubDate": ISODate("2021-08-04T00:00:00Z"),
        "show_id": 1
      }
    ],
    "show": 1
  }
]