MongoDB - How to update an object in an array?

Question

My data structure looks like this:

{
  "_id" : .....,
  "topicId" : topicId1,
  "category": .....,
  "other things"....,
  "posts": [
    {postId:id1,
     username:.....,
     postBody: 'some text here' 
    },
     {postId:id2,
     username:.....,
     postBody: ' some other text here' 
    }
  ] 
}

My goal is to find a document where topicId equal to some Id, after that in the document find in posts an object where its postId equal to some Id, and finally update postBody in that object.

At the end it should look like this:

{
  "_id" : .....,
  "topicId" : topicId1,
  "category": .....,
  "other things"....,
  "posts": [
    {postId:id1,
     username:.....,
     postBody: 'some text here' 
    },
     {postId:id2,
     username:.....,
     postBody: 'HERE IS UPDATED TEXT' 
    }
  ] 
}

This is how i'm deleting a post:

  db.collection('topics').findOneAndUpdate({ 'topicId': topicId }, { $pull: { 'posts': { 'postId': postId } } })

But i have no idea how to update it based on my data structure. I'd appreciate any help.

Haruo · Accepted Answer · 2019-10-29 17:42:27Z

You can try this:

01) Example of Document:

{
  "topicId" : "5db85e379a17899b8ba631ca",
  "category": "category",
  "other things": "Other Things",
  "posts": [
    {
       postId: "5dae22702486f7d89ba7633c",
       username: "TheUserName",
       postBody: 'Some Text Here' 
    },
    {
       postId: "5db85e439a17899b8ba631cd",
       username: 'TheOtherUserName',
       postBody: 'Some Other Text Here' 
    }
  ] 
}

02) Query:

db.collection('topics').update(
    {"topicId" : "5db85e379a17899b8ba631ca"},
    { $set: { "posts.$[outer].postBody" : "HERE IS UPDATED TEXT" } },
    { multi: true, arrayFilters: [{"outer.postId" : "5db85e439a17899b8ba631cd"}]}
);

Robot · Accepted Answer · 2019-10-29 17:47:24Z

1

considering your data is

{
  "topicId" : "topicId1",
  "posts": [
    {"postId":"id1",
     "postBody": "some text here" 
    },
     {"postId":"id2",
     "postBody": "some other text here" 
    }
  ] 
}

you can use simple updateOne by filter and then $set

db.blah.updateOne({ topicId: 'topicId1', 'posts.postId': 'id2'  }, { $set: { 'posts.$.postBody': 'HERE IS UPDATED TEXT' }  })

edited Oct 29, 2019 at 17:47

answered Oct 29, 2019 at 17:40

Robot

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2 Comments

barrypicker Over a year ago

Your answer did not work and gave error SyntaxError: missing } after property list @(shell):1:41

Robot Over a year ago

a , was deleted by mistake after inline editing :), added to answer

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