How do you go about creating a unique object id for each document in a mass update?
I've tried,
db.foo.update({ objectId: null }, { $set: { objectId: new ObjectId() }}, { multi: true })
But that gives me the same object id for each document.
Because you're applying a unique value to each doc, you need to iterate over your collection and update the docs one at a time.
In the shell:
db.foo.find({ objectId: null }).forEach(function(doc) {
doc.objectId = new ObjectId();
db.foo.save(doc);
});
You cannot update multiple documents in a single command in MongoDb currently. You can update multiple documents with a common set of changes/updates, but you can not make unique changes to each document. You would need to create a loop to iterate over each document in the shell or your favorite programming language.
You can generate an object Id in MongoDB like this. You can iterate over your doc and use this mongo object id.
const ObjectId = require("mongodb").ObjectID;
const id = new ObjectId
console.log(id)
Related
How to create a unique ID for each element of an array field, where uniqueness is maintained globally for all documents of the collection?
Is it possible to specify create a unique index for this field?
You can make use of ObjectId data type. ObjectIds are 12-byte values that are guaranteed to be unique across all documents in a collection. You can specify an ObjectId as the value for a field in an array when inserting a new document.
For example, if you have following document:
{
_id: ObjectId("5f9b5a6d65c5f09f7b5a6d65"),
nameOfArrayField: []
}
You can use the following command to insert a new document:
db.collection.insertOne({
nameOfArrayField: [
{
id: new ObjectId(),
name: "Big Cat Public Safety Law"
}
]
});
To specify a unique index, you can use createIndex() method in the MongoDB shell.
db.collection.createIndex({ "nameOfArrayField.id": 1 }, { unique: true })
unique: true option ensures that the id field of the element array will be unique globally for all documents of the collection. It will prevent from inserting the duplicate element with the same id field in the array. Point to be noted that it is an asynchronous operation. You can use the db.collection.getIndexes() method to check if the index is created or not.
I wish to return just the document id's from mongo that match a find() query.
I know I can pass an object to exclude or include in the result set, however I cannot find a way to just return the _id field.
My thought process is returning just this bit of information is going to be way more efficient (my use case requires no other document data just the ObjectId).
An example query that I expected to work was:
collection.find({}, { _id: 1 }).toArray(function(err, docs) {
...
}
However this returns the entire document and not just the _id field.
You just need to use a projection to find what ya want.
collection.find({filter criteria here}, {foo: 0, bar: 0, _id: 1});
Since I don't know what your document collection looks like this is all I can do for you. foo: 0 for example is exclude this property.
I found that using the cursor object directly I can specify the required projection. The mongodb package on npm when calling toArray() is returning the entire document regardless of the projection specified in the initial find(). Fixed working example below that satisfies my requirements of just getting the _id field.
Example document:
{
_id: new ObjectId(...),
test1: "hello",
test2: "world!"
}
Working Projection
var cursor = collection.find({});
cursor.project({
test1: 0,
test2: 0
});
cursor.toArray(function(err, docs) {
// Importantly the docs objects here only
// have the field _id
});
Because _id is by definition unique, you can use distinct to get an array of the _id values of all documents as:
collection.distinct('_id', function(err, ids) {
...
}
you can do like this
collection.find({},'_id').toArray(function(err, docs) {
...
}
How do one create unique indexes for document's objects stored in array?
{
_id: 'documentId',
books: [
{
unique_id: 1,
title: 'Asd',
},
{
unique_id: 2,
title: 'Wsad',
}
...
]
}
One thing I can think of is autoincrementing. Or is there any mongo way to do so?
if you remove the _id field from your doc, mongo will automatically add one for you, which is:
guaranteed to be unique
contains the timestamp of creation
lots of other features.
see here: https://docs.mongodb.com/v3.2/reference/method/ObjectId/
Looking at the example object again, are you referring to the ids in the books array?
If so, you can assign them with ObjectIds as well, just like in the document root's _id field:
doc.books.forEach(x => { x.unique_id = new ObjectId() } );
Hi im trying to simply remove a document from a collection using mongoose but for some strange reason I cannot get it to work.
Here is the code:
function deleteUserevent()
{console.log('in delete User Event');
models.Userevent.remove({ _id: "5214f4050acb53fe31000004"}, function(err) {
if (!err){
console.log('deleted user event!');
}
else {
console.log('error');
}
});
}
Can anyone help me out on my syntax? I know the _id is stored as new ObjectId("5214f4050acb53fe31000004") but I have tried this with no joy?
Thanks.
In MongoDB, the "_id" field of documents is of type ObjectId, as you mentioned. This is not equal to a String, so running the query
db.userevent.remove({ _id: "5214f4050acb53fe31000004"});
will not match anything, and will not remove anything. Instead, you must search for a document where the _id field is an ObjectId with that value:
db.userevents.remove({ _id: ObjectId("5214f4050acb53fe31000004")});
In mongoose, you can use the findByIdAndRemove command to remove a document with a specific _id. This command takes either an ObjectId or a String as an argument, so
query = Userevent.findByIdAndRemove("5214f4050acb53fe31000004");
should work just fine.
Just add exec() after query.
It should work like this:
await models.Userevent.findByIdAndDelete("5214f4050acb53fe31000004").exec()
I need to insert a document if it doesn't exist. I know that the "upsert" option can do that, but I have some particular needs.
First I need to create the document with its _id field only, but only if it doesn't exist already. My _id field is a number generated by me (not an ObjectId). If I use the "upsert" option then I get "Mod on _id not allowed"
db.mycollection.update({ _id: id }, { _id: id }, { upsert: true });
I know that we can't use the _id in a $set.
So, my question is: If there any way to a "create if doesn't exists" atomically in mongodb?
EDIT:
As proposed by #Barrie this works (using nodejs and mongoose):
var newUser = new User({ _id: id });
newUser.save(function (err) {
if (err && err.code === 11000) {
console.log('If duplicate key the user already exists', newTwitterUser);
return;
}
console.log('New user or err', newTwitterUser);
});
But I still wonder if it is the best way to do it.
I had the same problem, but found a better solution for my needs. You can use that same query style if you simply remove the _id attribute from the update object. So if at first you get an error with this:
db.mycollection.update({ _id: id }, {$set: { _id: id, name: 'name' }}, { upsert: true });
instead use this:
db.mycollection.update({ _id: id }, {$set: { name: 'name' }}, { upsert: true });
This is better because it works for both insert and update.
UPDATE: Upsert with _id can be done without $setOnInsert, as explaind by #Barrie above.
The trick is to use $setOnInsert:{_id:1} with upsert, that way the _id is only written to if it's an insert, and never for updates.
Only, there was a bug preventing this from working until v2.6 - I just tried it on 2.4 and it's not working.
The workaround I use is having another ID field with a unique index. Eg. $setOnInsert:{myId:1}.
You can just use insert(). If the document with the _id you specify already exists, the insert() will fail, nothing will be modified - so "create if it doesn't exist" is what it's already doing by default when you use insert() with a user-created _id.
Please note that $setOnInsert don't work easily when you upsert a simple key => value object (not $set or other).
I need to use that (in PHP):
public function update($criteria , $new_object, array $options = array()){
// In 2.6, $setOnInsert with upsert == true work with _id field
if(isset($options['upsert']) && $options['upsert']){
$firstKey = array_keys($new_object)[0];
if(strpos($firstKey, '$')===0){
$new_object['$setOnInsert']['_id'] = $this->getStringId();
}
//Even, we need to check if the object exists
else if($this->findOne($criteria, ['_id'])===null){
//In this case, we need to set the _id
$new_object['_id'] = $this->getStringId();
}
}
return parent::update($criteria, $new_object, $options);
}