I've recently started using MongoDB, and while translating queries, I've stumbled upon a problem when trying to translate MySQL NOT IN query.
What I'm trying to do is find ids that are not present in another collection. I need a way to return how many of these ids there are and then a list of these ids.
In MySQL, these ids are in a table called songs and are named spotify_id. I am checking against a table named artists where the ids are called track_id.
MySQL Query:
SELECT spotify_id FROM songs WHERE spotify_id NOT IN (SELECT artists.track_id FROM artists)
My current code using MongoDB:
track_ids = artists.find({}, {'track_id': 1})
track_ids_list = [d.get('track_id') for d in track_ids]
# Getting amount of ids not present in artists
tracks_num = songs.count_documents({'spotify_id': {'$nin': track_ids_list}})
# Getting tracks not present in artists
tracks = songs.find({'spotify_id': {'$nin': track_ids_list}})
The MongoDB query seems to return a positive number of documents, even when all of the ids should be present in both collections. The MySQL query works perfectly on the same database.
Is there a better way to perform a NOT IN query in MongoDB?
Thank you!
Related
Is there a way to quickly check every table in a mongodb database with the column "title"? I need to identify every table or rather collection where there's a column with the word "title", is there a way to do this using a mongodb query?
In Mongo there is no straight forward query to check all collections and fields. Instead, you can get a list of all collections using getCollectionInfos and then query each collection to see if there exists the field that you are looking for.
db.getCollectionInfos().forEach(function(c){
result = db.getCollection(c.name).findOne({"title":{$exists:true}});
if(result != null){
print(c.name);
}
}
);
This will not look for nested documents, though.
I'm fairly new to mongodb but I was wondering if there's a way by which we can get 2 different results from same mongodb collection in one database call uisng mongo java driver with morphia.
I have a collection accounts and I'm fetching data based on a key accountId. I need below two results/outputs from this collection in one query.
count of all the documents where accountID is 'xyz'
ResultList of first N documents where accountID is 'xyz' AND resultSet is sorted by a timestamp field.
to resolve the second scenario I'm using:
..Query....limit(N).order("TimeField").field("TimeField").filter("accountID =", "xyz").asList();
This is working fine as per expectation but to get the total count (scenario 1) of all documents with accountId = 'xyz' needs another mongodb call, which I want to avoid.
MongoDB doesn't support such batching on queries, unfortunately. You'll have to execute two separate calls.
I'm trying to create a database using MongoDB. Since I have no experience with NoSQL database I'm having some troubles with designing the database.
I want to make a database where one student can be part of multiple sessions, and one session can contain multiple students (many-to-many). Also, each event is linked to one student inside one session.
So far I designed it like this:
Sessions:
Sessions.students = [student_id1, student_id2]
Student:
Students.sessions = [session_id1, session_id2]
But my problem is, where should I store the relation, in sessions or in student, or in both (like above)?
And is this the correct way to create the event relationships?
Event:
Event.studentid = [student_id1]
Event.sessionid = [session_id1]
1) If you need to find how many students are in each session and how many sessions each student attends.
For Many-Many relations in mongodb store id's in each other collections.
2) if one of the questions is relevant for your project then only store ids accordingly.
ex: if you need to find session information not student information then store
session.student=[studentid1, id2 id3]; student.session=[] not required
Can also use indexing for searching but dont use too much of it.
As a user you have 2 collections in the database called, students & sessions.
In students collection: each document contains an array of sessionIds & in sessions collection: each document contains array of studentIds.
To get data in list you need to use aggregation
Query for students like
students.aggregate({
//here write query using $match, $unwind, $lookup
//$unwind : sessionIds from sessions
})
Query for sessions like
sessions({
//here write query using $match, $unwind, $lookup
//$unwind : studentIds from students
})
QUERYING MONGODB: RETREIVE SHOPS BY NAME AND BY LOCATION WITH ONE SINGLE QUERY
Hi folks!
I'm building a "search shops" application using MEAN Stack.
I store shops documents in MongoDB "location" collection like this:
{
_id: .....
name: ...//shop name
location : //...GEOJson
}
UI provides to the users one single input for shops searching. Basically, I would perform one single query to retrieve in the same results array:
All shops near the user (eventually limit to x)
All shops named "like" the input value
On logical side, I think this is a "$or like" query
Based on this answer
Using full text search with geospatial index on Mongodb
probably assign two special indexes (2dsphere and full text) to the collection is not the right manner to achieve this, anyway I think this is a different case just because I really don't want to apply sequential filter to results, "simply" want to retreive data with 2 distinct criteria.
If I should set indexes on my collection, of course the approach is to perform two distinct queries with two distinct mehtods ($near for locations and $text for name), and then merge the results with some server side logic to remove duplicate documents and sort them in some useful way for user experience, but I'm still wondering if exists a method to achieve this result with one single query.
So, the question is: is it possible or this kind of approach is out of MongoDB purpose?
Hope this is clear and hope that someone can teach something today!
Thanks
I am trying to query out the data from my MongoDB database but there are some fields which I would like to omit as MongoDB will query the whole collections with id, n out.
I did this to limit the query but unfortunately only one field could be omitted but not the other which is the 'n' field. How can I omit two fields?
data = collection.find_one({"files_id": file_id},{"_id":0,"data":1})
And I also realized that my query for data has the field name (u'data') too, how can I query it so that it only returns the data? for this case it's a binary data
Example:
{u'data': Binary('\x00\x00\xed\x00\n\x00\x00\xd5\xa9\x00\x000\x00\x00\x00#\x00\x00\x0f\xff\xf0\x00\x0b\x80\x00\x00\x00
Kindly assist thanks!