This might be trivial, but when running 'insert' from Mongodb shell, I can't seem to retrieve the newly-generated _id :
db.coll.insert({someField:"someValue"});
var theId=??? /* How to get the _id of my newly inserted object? */
I know how to retrieve it through language specific drivers (java, node.js) but not from the Shell. So far I eliminated the following :
var x=db.coll.insert(...)
print(x);
// Doesn't work: x is undefined
var doc={...}
db.coll.insert(doc);
print(doc._id)
// Doesn't work, prints undefined
Thank you
Try this:
var doc={...}
db.coll.save(doc);
print(doc._id)
Note that db.collection.save() will update a document if it finds a match by _id. In your case, it will do an insert.
Honestly, I'm not quite sure why db.collection.insert() doesn't populate _id in your in-memory document...
Related
My question might be simple be here's some more context to it.
I have a MySQL DB, I've used an ETL tool to populate a MongoDBwith, however I couldn't manage to create proper ObjectId reference to it (I can only get a string of the ObjectId.
So far I've had an idea (maybe crazy but still.. could work)
I got this field populated like this in one document :
"field1" : "ObjectId('5d48845c456145ee9d1ccffde')",
What I would want to achieve through mongoDB is removing the first and last char to get (stripping the double quotes):
"field1" : ObjectId('5d48845c456145ee9d1ccffde'),
(note that MongoDB seems to automatically convert simple to Double quote after the change, so my reference become corret).
Problem is, I don't find anything close to a sort of Update script for MongoDB to achieve this.
Is there any way to do this ?
Using NodeJS could work, however, querying the document at this state doesn't return the field1 (probably cause it find it incorect)...
If its one time update, you can use the following query:
db.COLLECTION.aggregate([
{
$addFields:{
"field1":{
$toObjectId:{
$substrBytes:[
"$field1",
10,
24
]
}
}
}
},
{
$out:"COLLECTION"
}
])
In aggregation, the 'field1' is cast to ObjectId. Later on, the old data in the collection is replaced with the aggregated one.
I am trying to work with mongo shell and I am having challenges in storing the value inside of mongo shell
when I find a user in the document users, i store it in the variable doc
> var doc = db.users.find({"username":"anil"});
When I type doc in the mongo shell i see the json object
> doc
{ "_id" : ObjectId("57325aaa48d9231b11e5cb81"), "username" : "anil", "email" : "mongodb#gmail.com" }
However when I type doc again, i dont see anything. its gone.. what am I doing wrong here ?
> doc
>
It might be something simple but I am not getting it. Can someone point out what I am doing wrong ?
This because find returns a cursor and you can only consume all the value once. Here because you filter your document based on _id value, in the return cursor you only have one document which is consumed the first time you time. If you need to iterate your result many times, you will need to return an array that contains all the documents from the cursor using toArray, but in your case what you need is findOne
when you open a mongo shell it tries to find a mongod server and connects to test by default. when you assign some variable in mongo shell to some document in mongod, it actually fetches the document from the database, to get the same result again you need to connect to the database again (means you need to type var doc = db.users.find({"username":"anil"}); again). Unlike the scenario where you define var doc = 4 in shell and typing doc will return 4 every time.
If you want to stop transmission at the beginning and do some processing then you need to add null after it like
var doc = db.users.find({"username":"anil"});null;
// do your work on doc
an ex.
One other option could be to use the next() function of the find() cursor. This will give the value of the first record in to the variable and it will persist. Then any required operation can be done on the variable.
I'm trying to find a way to achieve the following pseudo function on the server.The fields likesRecieved likesShown and likesMatch in exist in a document within the Posts collection.
I require this function to perform for every document in post collection by default. This is because Id like the function to do this...
1) find value(s) that exist in likesRecieved and likedShown fields.
2) insert these value(s) in likesMatch field.
3) remove values found in operation 1 from likesRecieved and likesShown
This is what I am essentially trying to do on the server...
likesRecieved: idA, idB, idE, idF, idL
likesShown: idE, idC, idF
..perform a function to result in the following...
likesRecieved: idA, idB, idL
likesShown: idC,
likesMatch: idE, idF
This is my code to find the ids in both arrays for one document only. The likeMatch helper returns the userIds that may exist in both 'likesRecieved' and 'likesShown' fields within a selected document in Posts collection. The resulting value(s) are then inserting into the likesMatch field.
likeMatch: function() {
var selectedPostId = Session.get('postId'); // _id of document in Post collection
var arrayOfLikeRecieved = Posts.find({_id: selectedPostId}, {fields: {LikesRecieved: 1}}).fetch();
var sumArrayRecieved = _.chain(arrayOfLikeRecieved).pluck('LikesRecieved').flatten().value();
var arrayOfLikeShown = Posts.find({_id: selectedPostId}, {fields: {LikesShown: 1}}).fetch();
var sumArrayShown = _.chain(arrayOfLikeShown).pluck('LikesShown').flatten().value();
var duplicates = _.intersection(sumArrayRecieved, sumArrayShown);
Meteor.call('insertDuplicateIntoMatchField', duplicates);
},
MongoDB doesn't have hooks like some other databases do, so there's no way to automatically have a function called when a document is inserted.
You have a couple of options, though. One way would be to have a hook in your application that runs just before inserting the document to run your function. This could be achieved in meteor by using a Collection.deny function.
If you would prefer to have the function be executed in mongodb, then you'll have to call the function manually. The problem is just how to know when the document was inserted or updated. Luckily, meteor allows you to observe changes to a cursor. You could use that to make a call out to the database and run a stored procedure (function) whenever a document gets updated.
From the looks of the syntax for handling mongodb related things in meteor it seems that you always need to know the collection's name to update, insert, remove or anything to the document.
What I am wondering is if it's possible to get the collection's name from the _id field of a document in meteor.
Meaning if you have a document with the _id equal to TNTco3bHzoSFMXKJT. Now knowing the _id of the document you want to find which collection the document is located in. Is this possible through meteor's implementation of mongodb or vanilla mongodb?
As taken from the official docs:
idGeneration String
The method of generating the _id fields of new documents in this collection. Possible values:
'STRING': random strings
'MONGO': random Meteor.Collection.ObjectID values
The default id generation technique is 'STRING'.
Your best option would be to insert records within a pseudo transaction where the second step is to take the id and collection name to feed it into a reference collection. Then, you can do your lookups from that.
It would be pretty costly, though to construct your find's but might be a pattern worthwhile exploring if you are building an app where your users will be creating arbitrary data patterns.
You could accomplish this by doing a findOne on all of the collections:
var collectionById = function(id) {
return _.find(_.keys(this), function(name) {
if (this[name] instanceof Meteor.Collection) {
if (this[name].findOne(id)) {
return true;
}
}
});
};
I tested this on both the client and the server and it seemed to work when run in the global context.
I am trying to use mongodb's ObjectID to do a range query on the insertion time of a given collection. I can't really find any documentation that this is possible, except for this blog entry: http://mongotips.com/b/a-few-objectid-tricks/ .
I want to fetch all documents created after a given timestamp. Using the nodejs driver, this is what I have:
var timeId = ObjectId.createFromTime(timestamp);
var query = {
localUser: userId,
_id: {$gte: timeId}
};
var cursor = collection.find(query).sort({_id: 1});
I always get the same amount of records (19 in a collection of 27), independent of the timestamp. I noticed that createFromTime only fills the bytes in the objectid related to time, the other ones are left at 0 (like this: 4f6198be0000000000000000).
The reason that I try to use an ObjectID for this, is that I need the timestamp when inserting the document on the mongodb server, not when passing the document to the mongodb driver in node.
Anyone knows how to make this work, or has another idea how to generate and query insertion times that were generated on the mongodb server?
Not sure about nodejs driver in ruby, you can simply apply range queries like this.
jan_id = BSON::ObjectId.from_time(Time.utc(2012, 1, 1))
feb_id = BSON::ObjectId.from_time(Time.utc(2012, 2, 1))
#users.find({'_id' => {'$gte' => jan_id, '$lt' => feb_id}})
make sure
var timeId = ObjectId.createFromTime(timestamp) is creating an ObjectId.
Also try query without localuser