How to delete many relational document in MongoDB?

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Post collection 

 Post : 
    _id : 001,
    comments : [1,2,3] // ObjectId

Comment collection

 Comment: 
    { _id : 1, message : "Bar" },
    { _id : 2, message : "Foo" },
    { _id : 3, message : "Bazz" }

I want to delete a Post and all comments on this post. But How to delete all its comments ?

Update

PostSchema

{
    model: String,
    stock: Number,
    images: [String],
    price: Number,
    views: { type: Number, default: 1 },
    commentsCount: { type: Number, default: 0 },
    comments: [{ type: Schema.Types.ObjectId, ref: "postComments" }],
    postedBy: { type: String, ref: "publisherInfo" }
  },

postComments Schema 

{
    sender: String,
    createAt: { type: Date, default: Date.now },
    votes: { type: Number, default: 0 },
    contain: String
  },
mongoose mongodb
2 Answers

You can use findByIdAndDelete which will delete the document and returns it. Now we can dynamically create a comment id array, and use it with deleteMany and $in operator. So we just used two db access.

router.delete("/posts/:id", async (req, res) => {
  try {
    const result = await Post.findByIdAndDelete(req.params.id);

    let commentIds = result.comments.map((c) => c._id);

    await Comment.deleteMany({
      _id: {
        $in: commentIds,
      },
    });

    res.send("OK");
  } catch (err) {
    console.log(err);
    res.status(500).send("Something went wrong");
  }
});

If the post successfully deleted but comments can't be deleted for some technical reason, you may consider using transactions so that the operations both succeeds or fails.

user_117174580

This way you can be safe about the query and delete all of the comments. Remove the ObjectId(id) if you already have the id in ObjectId form

const Posts = db.collection('posts')
const Comments = db.collection('collection')
const postToBeDeleted = await Posts.findOne({_id: ObjectId('posts')})
if(postToBeDeleted){
    await Posts.deleteOne({_id: ObjectId('posts')}
    for(const comment of postToBeDeleted.comments)
        await Comments.deleteOne({_id: ObjectId(comment)})
}

user_92855230
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