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Lookup Operator In Mongodb



           from: <collection to join>,
           localField: <field from the input documents>,
           foreignField: <field from the documents of the "from" collection>,
           as: <output array field>

  1. The from specifies the collection to join with
  2. The localField specifies the field from the input document to match the foreign key in the from collection
  3. The foreignField specifies the field of the from collection to match with the localField
  4. The as field specifies the name the output array


Picture showing the Articles Collection in MongoDB
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Picture showing the ArticlesComments Collection in MongoDB
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$Lookup Operator

db.Articles.aggregate([ { $lookup: { from: "ArticlesComments", localField: "_id", foreignField: "_subjectid", as: "ArticleDetails" } }])


Picture showing the output of Lookup Operator In Mongodb
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Posted By  -  Karan Gupta
Posted On  -  Friday, May 5, 2023
Updated On  -  Friday, October 13, 2023


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