mongodb db.getCollectionNames()command will give you all collection names what are all there in the current db, in a list.
I want the same output using pymongo. I googled some time and couldn't find anything like that.
Is anything like that exists ?
collection_names()
Will show you the collections of the current database.
From documentation:
collection_names()
Get a list of all the collection names in this database.
[read more]
Since pymongo 3.7, collection_names() is deprecated and the correct way to get collection names is list_collection_names()
Related
I am using MongoDB Compass. I'm creating my queries in Compass query language (programming-language-agnostic, so I can port it over to other languages later via Compasss). My problem? I can't figure out what I'm doing wrong in this query. There are no docs explaining MongoDB Compass syntax for $search.
My indexed text field is called markdown_1, my query is "my" (or whatever the user enters), and the object that is being searched looks like this:
How do I get this query to return anything? As of now, it finds nothing.
Thanks!
I am using PyMongo to insert data (title, description, phone_number ...) into MongoDB. However, when I use mongo client to view the data, it displays the properties in a strange order. Specifically, phone_number property is displayed first, followed by title and then comes description. Is there some way I can force a particular order?
The above question and answer are quite old. Anyhow, if somebody visits this I feel like I should add:
This answer is completely wrong. Actually in Mongo Documents ARE ordered key-value pairs. However when using pymongo it will use python dicts for documents which indeed are not ordered (as of cpython 3.6 python dicts retain order, however this is considered an implementation detail). But this is a limitation of the pymongo driver.
Be aware, that this limitation actually impacts the usability. If you query the db for a subdocument it will only match if the order of the key-values pairs is correct.
Just try the following code yourself:
from pymongo import MongoClient
db = MongoClient().testdb
col = db.testcol
subdoc = {
'field1': 1,
'field2': 2,
'filed3': 3
}
document = {
'subdoc': subdoc
}
col.insert_one(document)
print(col.find({'subdoc': subdoc}).count())
Each time this code gets executed the 'same' document is added to the collection. Thus, each time we run this code snippet the printed value 'should' increase by one. It does not because find only maches subdocuemnts with the correct ordering but python dicts just insert the subdoc in arbitrary order.
see the following answer how to use ordered dict to overcome this: https://stackoverflow.com/a/30787769/4273834
Original answer (2013):
MongoDB documents are BSON objects, unordered dictionaries of key-value pairs. So, you can't rely on or set a specific fields order. The only thing you can operate is which fields to display and which not to, see docs on find's projection argument.
Also see related questions on SO:
MongoDB field order and document position change after update
Can MongoDB and its drivers preserve the ordering of document elements
Ordering fields from find query with projection
Hope that helps.
Is there any way to find last update Document in Collection? in other way sort collection by update
somethings like this
people = Person.objects.order_by_update()
or i must add update time for each doc?
I use mongodb, mongoengine, flask
You must add a field such as last_updated_time if you want to be able to sort in this way. Also, since you're sorting on it, you should probably index it.
The only thing that mongodb stores by default is _id, which can be used roughly as a created_time timestamp.
I have a Rails 3 app using MongoDB, with Mongoid as the ORM. I'd like to query for a specific field within a collection.
To query for all records of a particular collection I use User.all.to_a, as an equivalent to User.all in ActiveRecord.
Now I'd like to query for all records within a collection, but only output a particular field. In this case I'd like to see all User names. How do I do this?
I'm sure I've stared right at this in the Mongoid documentation and am just missing something...
I couldn't locate it in the new documentation for mongoid, but here is a quick link to only pointing to old 2.x.x documentation.
Basically you need to do:
User.all.only(:name).to_a
What I want:
I have a master collection of products, I then want to filter them and put them in a separate collection.
db.masterproducts.find({category:"scuba gear"}).copyTo(db.newcollection)
Of course, I realise the 'copyTo' does not exist.
I thought I could do it with MapReduce as results are created in a new collection using the new 'out' parameter in v1.8; however this new collection is not a subset of my original collection. Or can it be if I use MapReduce correctly?
To get around it I am currently doing this:
Step 1:
/usr/local/mongodb/bin/mongodump --db database --collection masterproducts -q '{category:"scuba gear"}'
Step 2:
/usr/local/mongodb/bin/mongorestore -d database -c newcollection --drop packages.bson
My 2 step method just seems rather inefficient!
Any help greatly appreciated.
Thanks
Bob
You can iterate through your query result and save each item like this:
db.oldCollection.find(query).forEach(function(x){db.newCollection.save(x);})
You can create small server side javascript (like this one, just add filtering you want) and execute it using eval
You can use dump/restore in the way you described above
Copy collection command shoud be in mongodb soon (will be done in votes order)! See jira feature.
You should be able to create a subset with mapreduce (using 'out'). The problem is mapreduce has a special output format so your documents are going to be transformed (there is a JIRA ticket to add support for another format, but I can not find it at the moment). It is also going to be very inefficent :/
Copying a cursor to a collection makes a lot of sense, I suggest creating a ticket for this.
there is also toArray() method which can be used:
//create new collection
db.creatCollection("resultCollection")
// now query for type="foo" and insert the results into new collection
db.resultCollection.insert( (db.orginialCollection.find({type:'foo'}).toArray())