What I'm trying to do is take a user's query client side (via search function), send it to server via Meteor methods and if there is a search result, insert that query into another MongoDB instance? I need this in order to display search results from the user into client.
Something like this from server side:
UserSearch: function(query){
var init = Table.find({userId: this.userId}, {data: {Name: query}});
Search.insert({userId: this.userId, data: init});
},
Obviously, that doesn't work. But I'm looking for a way to allow to insert a query from one database into a new database.
So I think there are two pieces two your question here:
How do I connect to another MongoDB instance?
How do I insert data from one query result into a collection?
For #1, referencing this SO question, you can do:
var database = new MongoInternals.RemoteCollectionDriver("<mongo url>");
Search = new Mongo.Collection("search", { _driver: database });
For #2, you're simply missing the .fetch() as MasterAM pointed out:
UserSearch: function(query){
var init = Table.find({userId: this.userId, 'data.Name': query}).fetch();
Search.insert({userId: this.userId, data: init});
},
I also modified your Table query a bit as I don't think it's working in the current form. You want each field property in a query object to be in the same object. Note that the fetch will give you an array of Table objects, so you'll need to have your data field in your Search collection reflect that.
I am using reactivemongo to connect to MongoDB.
val connection: MongoConnection = driver.connection(hosts, options = conOpts, authentications = List(credentials))
val db = connection(database)
val collection = db(collection)
val resultData = collection.find(query, filter)
And the first time I try to query the database, I get a:
Error executing MongoDB Query reactivemongo.core.errors.DetailedDatabaseException: DatabaseException['not authorized for query on test.test' (code = 13)]
If I try again, the query usually succeeds. I presume that this is because the authentication hasn't had time to successfully complete when the find method is called for the first time.
So I wonder if there is a way to check the status of the authentication in order to wait for its completion before querying the database?
Reactivemongo > 0.11.x should support SHA1 authorization but is not the default, to enable it just add "?authMode=scram-sha1" at the end of your mongodb.uri
uri = "mongodb://userName:password#localhost/databaseName?authMode=scram-sha1"
in order to proper set up users just follow official doc:
https://docs.mongodb.com/manual/tutorial/enable-authentication/
details about roles:
https://docs.mongodb.com/manual/tutorial/enable-authentication/
Am using Spring-Data-Mongo to access do CRUD operations on my mongo database. I execute the below line
DB db = mongoTemplate.getDb()
When am in debug mode I can see that db._collections properties has 4 values (collections that I inserted). But when I query for
db.getCollectionNames()
I get zero collections back. Why is that? Same is also true when I do
db.getCollection("collectionName")
But I know the collections do exists because when I do something like
mongoTemplate.createCollection("collectionName");
I get an exception saying that collection already exists. Can anyone please explain what I might be missing
MongoTemplate provides a few methods for managing collections. The following example demonstrates some of the methods:
DBCollection collection = null;
if (!mongoTemplate.getCollectionNames().contains("collectionName")) {
collection = mongoTemplate.createCollection("collectionName");
}
mongoTemplate.dropCollection("collectionName");
In the above, getCollectionNames() returns a set of collection names and dropCollection() drops the collection.
Use MongoClient, MongoDatabase, and MongoIterable of com.mongodb.client and com.mongodb package.
MongoClient client = MongoClient(<host>, port);
MongoDatabase db = client.getDatabase(<Name of the database>);
MongoIterable<String> = db.listCollectionNames();
And now you can iterate over all the names of the collections.
Additionally, you even can use MongoCollection class to get the Document from the specified collection. The getCollection() will create collection if not present.
MongoCollection<Document> collection = db.getCollection(<Collection name>);
I'm creating a sort of background job queue system with MongoDB as the data store. How can I "listen" for inserts to a MongoDB collection before spawning workers to process the job?
Do I need to poll every few seconds to see if there are any changes from last time, or is there a way my script can wait for inserts to occur?
This is a PHP project that I am working on, but feel free to answer in Ruby or language agnostic.
What you are thinking of sounds a lot like triggers. MongoDB does not have any support for triggers, however some people have "rolled their own" using some tricks. The key here is the oplog.
When you run MongoDB in a Replica Set, all of the MongoDB actions are logged to an operations log (known as the oplog). The oplog is basically just a running list of the modifications made to the data. Replicas Sets function by listening to changes on this oplog and then applying the changes locally.
Does this sound familiar?
I cannot detail the whole process here, it is several pages of documentation, but the tools you need are available.
First some write-ups on the oplog
- Brief description
- Layout of the local collection (which contains the oplog)
You will also want to leverage tailable cursors. These will provide you with a way to listen for changes instead of polling for them. Note that replication uses tailable cursors, so this is a supported feature.
MongoDB has what is called capped collections and tailable cursors that allows MongoDB to push data to the listeners.
A capped collection is essentially a collection that is a fixed size and only allows insertions. Here's what it would look like to create one:
db.createCollection("messages", { capped: true, size: 100000000 })
MongoDB Tailable cursors (original post by Jonathan H. Wage)
Ruby
coll = db.collection('my_collection')
cursor = Mongo::Cursor.new(coll, :tailable => true)
loop do
if doc = cursor.next_document
puts doc
else
sleep 1
end
end
PHP
$mongo = new Mongo();
$db = $mongo->selectDB('my_db')
$coll = $db->selectCollection('my_collection');
$cursor = $coll->find()->tailable(true);
while (true) {
if ($cursor->hasNext()) {
$doc = $cursor->getNext();
print_r($doc);
} else {
sleep(1);
}
}
Python (by Robert Stewart)
from pymongo import Connection
import time
db = Connection().my_db
coll = db.my_collection
cursor = coll.find(tailable=True)
while cursor.alive:
try:
doc = cursor.next()
print doc
except StopIteration:
time.sleep(1)
Perl (by Max)
use 5.010;
use strict;
use warnings;
use MongoDB;
my $db = MongoDB::Connection->new;
my $coll = $db->my_db->my_collection;
my $cursor = $coll->find->tailable(1);
for (;;)
{
if (defined(my $doc = $cursor->next))
{
say $doc;
}
else
{
sleep 1;
}
}
Additional Resources:
Ruby/Node.js Tutorial which walks you through creating an application that listens to inserts in a MongoDB capped collection.
An article talking about tailable cursors in more detail.
PHP, Ruby, Python, and Perl examples of using tailable cursors.
Check out this: Change Streams
January 10, 2018 - Release 3.6
*EDIT: I wrote an article about how to do this https://medium.com/riow/mongodb-data-collection-change-85b63d96ff76
https://docs.mongodb.com/v3.6/changeStreams/
It's new in mongodb 3.6
https://docs.mongodb.com/manual/release-notes/3.6/ 2018/01/10
$ mongod --version
db version v3.6.2
In order to use changeStreams the database must be a Replication Set
More about Replication Sets:
https://docs.mongodb.com/manual/replication/
Your Database will be a "Standalone" by default.
How to Convert a Standalone to a Replica Set: https://docs.mongodb.com/manual/tutorial/convert-standalone-to-replica-set/
The following example is a practical application for how you might use this.
* Specifically for Node.
/* file.js */
'use strict'
module.exports = function (
app,
io,
User // Collection Name
) {
// SET WATCH ON COLLECTION
const changeStream = User.watch();
// Socket Connection
io.on('connection', function (socket) {
console.log('Connection!');
// USERS - Change
changeStream.on('change', function(change) {
console.log('COLLECTION CHANGED');
User.find({}, (err, data) => {
if (err) throw err;
if (data) {
// RESEND ALL USERS
socket.emit('users', data);
}
});
});
});
};
/* END - file.js */
Useful links:
https://docs.mongodb.com/manual/tutorial/convert-standalone-to-replica-set
https://docs.mongodb.com/manual/tutorial/change-streams-example
https://docs.mongodb.com/v3.6/tutorial/change-streams-example
http://plusnconsulting.com/post/MongoDB-Change-Streams
Since MongoDB 3.6 there will be a new notifications API called Change Streams which you can use for this. See this blog post for an example. Example from it:
cursor = client.my_db.my_collection.changes([
{'$match': {
'operationType': {'$in': ['insert', 'replace']}
}},
{'$match': {
'newDocument.n': {'$gte': 1}
}}
])
# Loops forever.
for change in cursor:
print(change['newDocument'])
MongoDB version 3.6 now includes change streams which is essentially an API on top of the OpLog allowing for trigger/notification-like use cases.
Here is a link to a Java example:
http://mongodb.github.io/mongo-java-driver/3.6/driver/tutorials/change-streams/
A NodeJS example might look something like:
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect("mongodb://localhost:22000/MyStore?readConcern=majority")
.then(function(client){
let db = client.db('MyStore')
let change_streams = db.collection('products').watch()
change_streams.on('change', function(change){
console.log(JSON.stringify(change));
});
});
Alternatively, you could use the standard Mongo FindAndUpdate method, and within the callback, fire an EventEmitter event (in Node) when the callback is run.
Any other parts of the application or architecture listening to this event will be notified of the update, and any relevant data sent there also. This is a really simple way to achieve notifications from Mongo.
Many of these answers will only give you new records and not updates and/or are extremely ineffecient
The only reliable, performant way to do this is to create a tailable cursor on local db: oplog.rs collection to get ALL changes to MongoDB and do with it what you will. (MongoDB even does this internally more or less to support replication!)
Explanation of what the oplog contains:
https://www.compose.com/articles/the-mongodb-oplog-and-node-js/
Example of a Node.js library that provides an API around what is available to be done with the oplog:
https://github.com/cayasso/mongo-oplog
There is an awesome set of services available called MongoDB Stitch. Look into stitch functions/triggers. Note this is a cloud-based paid service (AWS). In your case, on an insert, you could call a custom function written in javascript.
Actually, instead of watching output, why you dont get notice when something new is inserted by using middle-ware that was provided by mongoose schema
You can catch the event of insert a new document and do something after this insertion done
There is an working java example which can be found here.
MongoClient mongoClient = new MongoClient();
DBCollection coll = mongoClient.getDatabase("local").getCollection("oplog.rs");
DBCursor cur = coll.find().sort(BasicDBObjectBuilder.start("$natural", 1).get())
.addOption(Bytes.QUERYOPTION_TAILABLE | Bytes.QUERYOPTION_AWAITDATA);
System.out.println("== open cursor ==");
Runnable task = () -> {
System.out.println("\tWaiting for events");
while (cur.hasNext()) {
DBObject obj = cur.next();
System.out.println( obj );
}
};
new Thread(task).start();
The key is QUERY OPTIONS given here.
Also you can change find query, if you don't need to load all the data every time.
BasicDBObject query= new BasicDBObject();
query.put("ts", new BasicDBObject("$gt", new BsonTimestamp(1471952088, 1))); //timestamp is within some range
query.put("op", "i"); //Only insert operation
DBCursor cur = coll.find(query).sort(BasicDBObjectBuilder.start("$natural", 1).get())
.addOption(Bytes.QUERYOPTION_TAILABLE | Bytes.QUERYOPTION_AWAITDATA);
After 3.6 one is allowed to use database the following database triggers types:
event-driven triggers - useful to update related documents automatically, notify downstream services, propagate data to support mixed workloads, data integrity & auditing
scheduled triggers - useful for scheduled data retrieval, propagation, archival and analytics workloads
Log into your Atlas account and select Triggers interface and add new trigger:
Expand each section for more settings or details.
Using the c# driver for MongoDB I can easily construct a query against which I can then add SetSkip() and SetLimit() parameters to constrict the result set to a certain size.
However I'd like to be able to know what item count of the query would be before applying Skip and Take without executing the query and loading the entire result set (which could be huge) into memory.
It looks like I can do this with MongoDB directly through the shell by using the count() command. e.g.:
db.item.find( { "FieldToMatch" : "ValueToMatch" } ).count()
Which just returns an integer and that's exactly what I want. But I can't see a way in the documentation of doing this through the C# driver. Is it possible?
(It should be noted that we're already using the query builder extensively, so ideally I'd much rather do this through the query builder than start issuing commands down to the shell through the driver, if that's possible. But if that's the only solution then an example would be helpful, thanks.)
Cheers,
Matt
You can do it like this:
var server = MongoServer.Create("mongodb://localhost:27020");
var database = server.GetDatabase("someDb");
var collection = database.GetCollection<Type>("item");
var cursor = collection.Find(Query.EQ("FieldToMatch" : "ValueToMatch"));
var count = cursor.Count();
Some notes:
You should have only one instance of server (singleton)
latest driver version actually returns long count instead of int
Cursor only fetches data once you iterate
You can configure a lot of things like skip, take, specify fields to return in cursor before actually load data (start iteration)
Count() method of cursor loads only document count
I'm using the Driver 2.3.0 and now is also possible to do that like this:
...
IMongoCollection<entity> Collection = db.GetCollection<entity>(CollectionName);
var yourFilter = Builders<entity>.Filter.Where(o => o.prop == value);
long countResut = Collection.Count(yourFilter);