What is the proper way to delete all elements from an array?

Question

I am having trouble in deleting all elements from an array in mongodb. This is my schema:

const userSchema=mongoose.Schema({
    name: String,
    email: String,
    password: String,
    blog: [{
        date: Date,
        post: String
    }],
    week: [{
        weekday: String,
        tasks:[String]
    }],
    todo: [String]
});

const User= mongoose.model("User", userSchema);

I want to delete all data from todo but it is not working. Here is the code for that:

app.post("/deletelist",(req,res) =>{
    console.log(req.body);
    const user = req.body.userid;
    console.log(user);

    // User.find({_id: user}, async function(err, foundUser){
    //     if(err){
    //         console.log(err);
    //     } else{
    //         foundUser.updateOne({},{ $set : {"todo": [] }} , {multi:true});
    //         // await foundUser.save();
    //         res.send("ToDo Deleted");
    //     }
    // });

    User.updateOne({_id:user},{ $set : {"todo": []}}, {multi:true});
    res.send("ToDo Deleted");

});

I am getting user from the frontend. The part that is commented and the other one(User.updateOne) both are not working. I'll be glad if anyone can help

I think the issue is that `{ $set: {"todo": [] } }` will not do anything because it's already an array and you don't provide specific values. I think I had this issue on one of my side projects. I ended up doing something like `{ $unset: {"todo": true } }` and right after this I called `{ $set: {"todo": [] } }`, but be careful because this operation is not atomic — Tim Nimets, Feb 15 '22 at 18:11
@Akshat I have found this code on the internet which looks prettier. `db.users.update({username: "tom"}, {$pull: {documents: {$exists: true}}})` you should try both. Also this issue is not directly from mongodb, but most likely from mongodb node driver, since manual updates in the console seem to works for me. — Tim Nimets, Feb 16 '22 at 02:57

Abdelrhman Mohamed · Accepted Answer · 2022-02-15T18:39:39.737

1

Updated

You cannot use multi-option in the updateOne method remove it and it will work

Example

User.updateOne({_id:user},{ $set : {"todo": []}})

edited Feb 15 '22 at 18:39

answered Feb 15 '22 at 18:12

Abdelrhman Mohamed

167
11

I tried that earlier, it's saying that it's deprecated use UpdateOne or UpdateMany instead. – Akshat Feb 15 '22 at 18:16
I just tried the code in the MongoDB shell and it's working fine for me db.users.updateOne({id: 1}, {$set: {"todo": []}}) – Abdelrhman Mohamed Feb 15 '22 at 18:35
Look to the update! – Abdelrhman Mohamed Feb 15 '22 at 18:40
It started working after I added a callback function to it. – Akshat Feb 16 '22 at 08:52
User.updateOne({_id:user},{ $set : {"todo": []}}, function(err, docs){ if(err){ console.log(clg); } else{ console.log(docs); res.send("ToDo Deleted"); } }); – Akshat Feb 16 '22 at 08:52
I am not sure why a callback was mandatory to make it work. Please tell me if you know the reason for that. Thanks – Akshat Feb 16 '22 at 08:53

score 1 · Answer 2 · answered Feb 15 '22 at 18:59

1

this will remove all the elements even the key if you want to remove the elements only try @Abdelrhman answer

User.updateOne({_id:user},{$unset:{todo:""}})

answered Feb 15 '22 at 18:59

Super sub

269
2
8

What is the proper way to delete all elements from an array?

2 Answers2

Updated