Question 300448 in Mongodb Question posted in
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Mongodb update of nested array

I have a collection:

[
  {
    users: [user2, user4]
  },
  {
    users: [user1, user2, user3]
  },
  {
    users: [user1, user3, user4]
  }
]

nested property "users" cannot contain the same user twice.

I find out that user2 is actually the same user as user1, so I update my documents.
My final result should look like this:

[
  {
    users: [user1, user4]
  },
  {
    users: [user1, user3]
  },
  {
    users: [user1, user3, user4]
  }
]

Document1 is updated: user2 becomes user1.
Document2 is updated: user2 is removed since user1 already exists.
Document3 is not updated.

The order of the users is not important.

How can I achieve this with updateMany?

Tags:

2

Answers


  1. 0

    you can use the $addToSet operator to ensure unique values in the "users" array. Here’s an example using the MongoDB Node.js driver:

    const MongoClient = require('mongodb').MongoClient;

async function updateDocuments() {
  const uri = 'mongodb://localhost:27017'; // Your database URI
  const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });

  try {
    await client.connect();

    const database = client.db('your-database-name');
    const collection = database.collection('your-collection-name');

    // Update documents using updateMany
    await collection.updateMany(
      {},
      {
        $addToSet: {
          users: { $each: ['user1', 'user2'] } // Add all users to ensure uniqueness
        }
      }
    );

    // Remove user2 from all documents
    await collection.updateMany(
      { users: 'user2' },
      {
        $pull: {
          users: 'user2'
        }
      }
    );

    console.log('Documents updated successfully');
  } finally {
    await client.close();
  }
}

updateDocuments();
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  2. 0

    Use $filter to get array without user2. $setUnion with an array [user1] to get the final users set

    db.collection.updateMany({
  users: "user2"
},
[
  {
    "$set": {
      "users": {
        "$setUnion": [
          {
            "$filter": {
              "input": "$users",
              "as": "u",
              "cond": {
                $ne: [
                  "$$u",
                  "user2"
                ]
              }
            }
          },
          [
            "user1"
          ]
        ]
      }
    }
  }
])

    Mongo Playground

    Playground does not allow usage of updateMany. You can ignore {multi: true} in the playground as it is simply a workaround/alternative to updateMany

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