I'm trying to create a registration form with mongoose and MongoDB. I have a unique key, UserId, and every time I create a new entry I would like to take the greatest UserId in the database and increase it by one.
I tried with db.user.find({}).sort({userId: 1}); but it seems not to work.
Thanks
Masiar
What you want to do sounds more like a Schema for Relational Databases with an Auto Increment. I would recommend another solution.
At first you already have a unique id. It get automatically created and are in "_id" field. For me it seems you want to have a UserID for building relation, but you already ca use the value in _id.
The other thing why you want incremented ids could be that you create a webapplication and propably want "nicer" urls? For example. /user/1 instead of /user/abc48df...?
If that is the case i would prefer to create a unique constraint on a username. And instead of an id you use you username in the url "/user/john".
With this your urls are much nicer. And for building relation you can use _id. And you don't run into problems with fethcing the highest number first.
To create a unique index:
db.collection.ensureIndex({username: 1}, {unique: true})
You can do this to get the user with the current highest UserId:
db.user.insert( { UserId: 1 } )
db.user.insert( { UserId: 2 } )
db.user.insert( { UserId: 3 } )
db.user.find().sort( { UserId: -1 } ).limit(1)
It's worth noting that there isn't a way in MongoDB to fetch this value and insert a new user in a single atomic transaction, it only supports atomic operations on single documents. You'd need to take care that another operation didn't insert another user at the same time, you could end up with two users with the same UserId.
To iterate over the cursor and get put the returned doc in an array:
var myArray = [];
User.find().sort('UserId','descending').limit(1).each(function(err, doc) {
myArray.push(doc);
});
Related
I've been struggling with mongodb for some time now, and the idea is quite simple: I have a collection, and I want o to add a new ID field. This field is controlled by our API, and it auto increments it for each new document inserted.
The thing is, the collection already has some documents, so I must initialize each document with a number sequentially, no matter the order:
collection: holiday {
'date': date,
'name': string
}
The collection has 12 documents, so each document should get an ID property, with values from 1 to 12. What kind of query or function should I use to do this? No restrictions so far, and performance is not a problem.
Maybe it is not optimal but works :)
var newId = 1;
var oldIds = [];
db.holiday.find().forEach(it => {
const documentToMigrate = it;
oldIds.push(it._id);
documentToMigrate._id = newId;
db.holiday.save(documentToMigrate);
++newId;
})
db.holiday.remove({_id: {$in: oldIds}});
I am using mongodb to save user information. There is a userId field in that collection. I get many userIds in my application and saved as an array. I need to query whether all the userIds in that array exist in the collection. If not, find out all the missing ones. Is there one query command does the work? I don't want to query the userId one by one. So what is the better way to achieve this?
The user collection is very simple as below and there is no nested data.
userId: String
name: String
gender: String
phone: String
For example, I have an array of ids [1, 2, 3]. I have to run query three times to check whether these are users to match the three ids.
This can be done with the $in operator.
Example:
db.users.find( {userId: { $in: [ 1, 2, 3 ] } } );
Once you have the users pulled back from that you can determine in the application layer which users did not come back.
Although I think it is a general question, I could not find a solution that matches my needs.
I have 2 Mongo collections. The 'users' collection and the second one 'dbInfos'.
Now, I have a template called 'Infos' and want the already existing fields in the Mongo collections to be presented to the user in input fields in case there is data in the collection. When no data is provided in the database yet, it should be empty.
So here is my code, which works fine until I want to capture the fields from the second collection.
Template.Infos.onRendered(function() {
$('#txtName').val(Meteor.user().profile.name);
$('#txtEmail').val(Meteor.user().emails[0].address);
});
These 2 work great.
But I don´t know how to query the infos from the collection 'dbInfos', which is not the 'users' collection. Obviously Meteor.user().country does not work, because it is not in the 'users' collection. Maybe a find({}) query? However, I don´t know how to write it.
$('#txtCountry').val( ***query function***);
Regarding the structure of 'dbInfos': Every object has an _id which is equal to the userId plus more fields like country, city etc...
{
"_id": "12345",
"country": "countryX",
"city": "cityY"
}
Additionally, how can I guarantee that nothing is presented, when the field in the collection is empty? Or is this automatic, because it will just return an empty field?
Edit
I now tried this:
dbInfos.find({},{'country': 1, '_id': 0})
I think this is the correct syntax to retrieve the country field and suppress the output of the _id field. But I only get [object Object] as a return.
you're missing the idea of a foreign key. each item in a collection needs a unique key, assigned by mongo (usually). so the key of your country info being the same as the userId is not correct, but you're close. instead, you can reference the userId like this:
{
"_id": "abc123",
"userId": "12345",
"country": "countryX",
"city": "cityY"
}
here, "abc123" is unique to that collection and assigned by mongo, and "12345" is the _id of some record in Meteor.users.
so you can find it like this (this would be on the client, and you would have already subscribed to DBInfos collection):
let userId = Meteor.userId();
let matchingInfos = DBInfos.find({userId: userId});
the first userId is the name of the field in the collection, the second is the local variable that came from the logged in user.
update:
ok, i think i see where you're getting tripped it. there's a difference between find() and findOne().
find() returns a cursor, and that might be where you're getting your [object object]. findOne() returns an actual object.
for both, the first argument is a filter, and the second argument is an options field. e.g.
let cursor = DBInfos.find({
userId: Meteor.userId()
},
{
fields: {
country: 1
}
});
this is going to:
find all records that belong to the logged in user
make only the country and _id fields available
make that data available in the form of a cursor
the cursor allows you to iterate over the results, but it is not a JSON object of your results. a cursor is handy if you want to use "{{#each}}" in the HTML, for example.
if you simply change the find() to a findOne():
let result = DBInfos.findOne({ /** and the rest **/
... now you actually have a JSON result object.
you can also do a combination of find/fetch, which works like a findOne():
let result = DBInfos.find({
userId: Meteor.userId()
},
{
fields: {
country: 1
}
}).fetch();
with that result, you can now get country:
let country = result.country;
btw, you don't need to use the options to get country. i've been assuming all this code is on the client (might be a bad assumption). so this will work to get the country as well:
let result = DBInfos.findOne({userId: Meteor.userId()});
let country = result.country;
what's going on here? it's just like above, but the result JSON might have more fields in it than just country and _id. (it depends on what was published).
i'll typically use the options field when doing a find() on the server, to limit what's being published to the client. on the client, if you just need to grab the country field, you don't really need to specify the options in that way.
in that options, you can also do things like sort the results. that can be handy on the client when you're going to iterate on a cursor and you want the results displayed in a certain order.
does all that make sense? is that what was tripping you up?
Is it good or bad practice to keep the standard "_id" generated my mongo in a document as well as my own unique identifier such as "name", or should I just replace _id generated with the actual name so my documents will look like this:
{
_id: 782yb238b2327b3,
name: "my_name"
}
or just like this:
{
_id: "my_name"
}
This depends on the scenario, there is nothing wrong with having your own unique ID, it may be string or a number, completely depends on your situation as long as its unique, the important thing is you are in charge of it. You would want to add an index to it of course.
for example i have an additional ID field which is a number called 'ID', because i required a sequential number as an identifier, another usecase may be that your migrating an application so you have to conform to a particular sequence pattern.
The sequences for the unique identifies could easily be stored in a separate document/collections.
There is no issue with using the built in _id if you have no requirement not to have a custom one, an interesting fact is that you can get the created date out of the _id. Always useful.
db.col.insert( { name: "test" } );
var doc = db.col.findOne( { name: "test" } );
var timestamp = doc._id.getTimestamp();
So i'm pretty new to mongoDb so i figure this could be a misunderstanding on general usage. so bear with me.
I have a document schema I'm working with as such
{
name: "bob",
email: "bob#gmail.com",
logins: [
{ u: 'a', p: 'b', public_id: '123' },
{ u: 'x', p: 'y', public_id: 'abc' }
]
}
My Problem is that i need to ensure that the public ids are unique within a document and collection,
Furthermore there are some existing records being migrated from a mySQL DB that dont have records, and will therefore all be replaced by null values in mongo.
I figure its either an index
db.users.ensureIndex({logins.public_id: 1}, {unique: true});
which isn't working because of the missing keys and is throwing a E11000 duplicate key error index:
or this is a more fundamental schema problem in that I shouldn't be nesting objects in an array structure like that. In which case, what? a seperate collection for the user_logins??? which seems to go against the idea of an embedded document.
If you expect u and p to have always the same values on each insert (as in your example snippet), you might want to use the $addToSet operator on inserts to ensure the uniqueness of your public_id field. Otherwise I think it's quite difficult to make them unique across a whole collection not working with external maintenance or js functions.
If not, I would possibly store them in their own collection and use the public_id as _id field to ensure their cross-document uniqueness inside a collection. Maybe that would contradict the idea of embedded docs in a doc database, but according to different requirements I think that's negligible.
Furthermore there are some existing records being migrated from a mySQL DB that dont have records, and will therefore all be replaced by null values in mongo.
So you want to apply a unique index on a data set that's not truly unique. I think this is just a modeling problem.
If logins.public_id is null that's going to violate your uniqueness constraint, then just don't write it at all:
{
logins: [
{ u: 'a', p: 'b' },
{ u: 'x', p: 'y' }
]
}
Thanks all.
In the end I opted to seperate this into 2 collections, one for users and one for logins.
users this looked a little like..
userDocument = {
...
logins: [
DBRef('loginsCollection', loginDocument._id),
DBRef('loginsCollection', loginDocument2._id),
]
}
loginDocument = {
...
user: new DBRef('userCollection', userDocument ._id)
}
Although not what i was originally after (a single collection) It is working niocely and by utilising the MongoId uniquness there is a constraint now built in at a database level and not implemented at the application level.