I am working on a Meteorjs application which is using MongoDB in back end.
In my collection there are some objects which are having a common field named parent_id eg
{name:'A',parent_id:'acd'}
{name:'b',parent_id:'acd'}
{name:'c',parent_id:'acd'}
{name:'d',parent_id:'acd'}
I want to copy all these objects in the database by changing the parent_id field eg
{name:'A',parent_id:'acdef'}
{name:'b',parent_id:'acdef'}
{name:'c',parent_id:'acdef'}
{name:'d',parent_id:'acdef'}
and these all objects will be in database like this
{name:'A',parent_id:'acd'}
{name:'b',parent_id:'acd'}
{name:'c',parent_id:'acd'}
{name:'d',parent_id:'acd'}
{name:'A',parent_id:'acdef'}
{name:'b',parent_id:'acdef'}
{name:'c',parent_id:'acdef'}
{name:'d',parent_id:'acdef'}
for this I have find the elements from the db which have parent_id:'abc'
items=db.collection.find({parent_id:'abc').fetch()
and using a loop i have changed the parent_id of each item and then tried this command
for(i=0;i<items.length;i++){
items[i].parent_id='abcdef';
meteor.collection.insert(item)
}
but it is giving me an errorduplicate for _id
Well it will unless you delete the _id value from the object first:
for(i=0;i<items.length;i++){
items[i].parent_id='abcdef';
delete items[i]["_id"];
meteor.collection.insert(item[i])
}
So the delete should clear that up and an new _id will be generated.
When you Collection.find() your documents you can use the field specifier to exclude the _id field.
var items = collection.find({}, {fields: {name: 1, parent_id: 1, _id: 0}).fetch();
Then when you modify and insert those documents again, they will be duplicates with each having its own unique _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.
This is my MongoDB query:
db.events.update({date:{$gte: ISODate("2014-09-01T00:00:00Z")}},{$set:{"artists.$.soundcloud_toggle":false}},{multi:true,upsert:false})
Apparently I cannot use "artists.$.soundcloud_toggle" to update all artist documents within the artists array:
"The $ operator can update the first array element that matches
multiple query criteria specified with the $elemMatch() operator.
http://docs.mongodb.org/manual/reference/operator/update/positional/"
I'm happy to run the query a number of times changing the index of the array in order to set the soundcloud_toggle property of every artist in every event that matches the query e.g
artists.0.soundcloud_toggle
artists.1.soundcloud_toggle
artists.2.soundcloud_toggle
artists.3.soundcloud_toggle
The problem is: when there is say, only one artist document in the artists array and I run the query with "artists.1.soundcloud_toggle" It will insert an artist document into the artist array with a single property:
{
"soundcloud_toggle" : true
},
(I have declared "upsert:false", which should be false by default anyways)
How do I stop the query from inserting a document and setting soundcloud_toggle:false when there is no existing document there? I only want it to update the property if an artist exists at the given artists array index.
If, like you said, you don't mind completing the operation with multiple queries, you can add an $exists condition to your filter.
E.g. in the 5th iteration, when updating index=4, add: "artists.4": {$exists: true}, like:
db.events.update(
{ date: {$gte: ISODate("2014-09-01T00:00:00Z")},
"artists.4": {$exists: true} },
{ $set:{ "artists.4.soundcloud_toggle" :false } },
{ multi: true, upsert: false }
)
I have a collection which have a document like this:
collection 1
{
_id: ObjectID(),
name: foo
}
I would get ObjectID of the above collection and copy into a document of another collection in order to reference correctly. Should I do simply:
db.collection1.find({name:"foo"},{_id:1})
EDIT
A call to find will return a cursor. Cursors works like an iterator in other languages. You can either attempt to find the first element in the cursor using the next() function and then get it's _id property or simplify your statement using findOne:
var x = db.collection1.findOne({name:"foo"}, {_id:1});
var id = x._id;
This is making an assumption that you are getting a document back from that query. You'll probably want to add a null check on x before grabbing the _id property.
I don't know why but if i try to update an existing field using the $set method, any existing fields are replaced in the same context.
For example. Say i have an existing collection with the following fields.
Name of collection: Ticket
{profile: {name: "Test", placement: 1}, requestor: _id}
When i attempt to add/update fields to this collection like this:
var ticket = Meteor.tickets.findOne({_id: ticketID});
if(ticket){
Meteor.users.update(ticket, {
$set: profile: {name: "Test2", new_fields: "value"}
});
}
The collection gets updated and the name field changes but placement is removed and no longer there. This is also true if i remove the name field. How do we properly update a meteor collection without having to keep passing the same structure over and over?
Just do this:
$set: {"profile.name": "Test2", "profile.new_fields": "value"}
I.e. You were replacing the whole hash. Instead you can update the fields within the hash.
if the field you want to change have a unique index, you can modify that particular field to what you want without destroying the remaining information in the field.
db.artists.find()
{"_id":ObjectId("1"),"name":"A1","media_id":["m1","m2" ]}
{"_id":ObjectId("2"),"name":"A2","media_id":["m2","m3"]}
{"_id":ObjectId("3"),"name":"A3","media_id":["m3","m1","m2"]}
db.artists.ensureIndex({"name":1})
db.artists.update(
{name:"A1"},
{$set: { name:"A4"}},
{ upsert: true }
)
b.artists.find()
{"_id":ObjectId("1"),"name":"A4","media_id":["m1","m2" ]}
{"_id":ObjectId("2"),"name":"A2","media_id":["m2","m3"]}
{"_id":ObjectId("3"),"name":"A3","media_id":["m3","m1","m2"]}
I am myself quite new in MongoDB but this worked pretty well for me.
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);
});