This page in the documentation says you can access a collection using c[name] or c.name, where c is a Collection, but what exactly does a sub-collection mean? I couldn't find any use of the term in the mongodb docs.
What I'm assuming, is that it gets the value of each document at key name, wihtin the collection, and represents that as its own collection. Is this the case?
A subcollection is just a naming convention of using . in a collection name as a way to organize your collection names.
So with the following code:
client = pymongo.MongoClient()
db = client['mydb']
coll = db['test']
subcoll = coll['subtest']
subcoll is a collection with a name of test.subtest. There's no defined relationship between test and test.subtest, it's just naming.
Related
use <databasename> will set a variable db to be the database
specified by <databasename>, so the database can be referred to
the variable db.
I wonder if a collection or document can also be
referred to by a variable, and if yes, how?
Every object in a MongoDB server has an identifier _id. If I am correct, a database, a collection and a document are objects.
How are the identifier of an object used in practice?
Both a database and a collection have a name. So we can refer to a
collection via its name e.g. mydb.mycollection.
Does a document also have a name?
Thanks.
A collection consists of several documents so a document as such do not have any name. _id distinguishes the documents. To fetch any particular document, you can filter it on the basis of _id or the data stored in it.
Referencing the db and then the collection in selected db will give you the required document.
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 was testing how to create database and collection mongo java driver.
MongoClient client = new MongoClient("localhost",27017);
DB db = client.getDB("ow");
DBCollection collection = db.getCollection("documents");
collection.save(new BasicDBObject("_id",1));
collection.remove(new BasicDBObject("_id",1));
boolean result = db.collectionExists("documents");
assertTrue(result);
assertNotNull(collection);
client.close();
I would prefer to use createCollection method on the DB object, but found that it does not create database / collection unless the first document is inserted.
My question is is this understanding correct ? Is above code correct was of creating collection or database.
prefer to use createCollection method on the DB object, but found that it does not create database / collection unless the first
document is inserted.
MongoDB creates a collection implicitly when the first document is saved into a collection. The createCollection() method explicitly creates a collection only and only if an options object is passed to it as an argument.
Now this makes sense. The options parameter can take in one or more arguments to decide the characteristics of the collection we want to create such as capped,autoIndexId,size,usePowerOf2Sizes,max no. of documents.
If we do not specify any of these options, the default behavior would take precedence, i.e create a collection lazily whenever the first insert is made, with default settings.
So if we want a collection whose characteristics we are going to define, then we can pass these characteristics as a DBObject to the createCollections() method and our collection would be created. Below is an example of how to pass the options.
BasicDBObject options = new BasicDBObject();
options.put("size", 12121212);
db.createCollection("hello", options);
Is above code correct was of creating collection or database.
Yes. It allows mongodb to apply the default configuration for your collection. Unless you want to set the
max,size,autoIndexId,capped,usePowerOf2Sizes properties for your new collection, this is fine.
Refer: http://docs.mongodb.org/manual/reference/method/db.createCollection/
If you create a Mongo document directly inside Mongo and want to access this same document via Meteor, what is the best way to accomplish this task?
I am getting undefined result when I attempt to access.
If you create a new document from Meteor it does not prefix the id with ObjectId("").
Any help would be greatly appreciated.
I want to simply find exact document by exact ObjectId.
Use Meteor.Collection.ObjectID:
var oid = new Meteor.Collection.ObjectID("a86ce44f9a46b99bca1be7a9");
var doc = SomeCollection.findOne(oid);
See the options for how unique IDs in collections are generated. However, it's general practice in Meteor to use the string approach because clients can then generate unique IDs reliably.
I have an ElasticSearch instance indexing a MongoDB database using the river by richardwilly98
There are two types of documents that are indexed:
documents referencing users
documents representing users
When these objects are added to mongodb richardwilly98's river generates something like the following:
document = {'user': {"$id" :
"5159a004c87126641f4f9530" } }
user_document = {'_id':"5159a004c87126641f4f9530",'username':'bob'}
If I perform a search for 'bob' i'd like any documents that reference the bob document to be returned. At the moment this doesn't happen because the username field is not related to the referencing documents in anyway.
Is it possible to do this? Does ElasticSearch have object references?
Thanks - let me know if I haven't been clear.
If each document belong to no more than one user, you can index documents as children of users. Then you can use has_parent filter to perform the search. However, if a single document can belong to more than one user, you will have to perform search in two steps. First you would have to find the user and then issue another search to find documents.
Elasticsearch supports parent field [1]. MongoDB river supports custom mapping [2] so _parent can now be used.
http://www.elasticsearch.org/guide/reference/mapping/parent-field/
https://github.com/richardwilly98/elasticsearch-river-mongodb/issues/64