I'm writing a Meteor (Node.js) app which uses MongoDB on the backend. At a certain point in my code, I need to update a specific document within a collection. I need to use Mongo's update() method, but I'm having trouble passing in the proper (complex) query to narrow down to that one, specific document. The document I'm trying to update is:
db.collection.find({market: 'AAA'}).sort({creationDate:-1}).limit(1)
In words, the one document in collection that has a market of AAA and was created most recently (creationDate is a UNIX timestamp number, e.g. 1408829429914). There are multiple documents with a market of AAA, so I am using sort() and limit(1) to find the document which was created most recently.
Mongo's update() doesn't seem to accept sorting parameters as part of the query before the update process. What can I do to narrow down to this document and update it? Thanks!
You will need to fetch the document you want and then update it by _id. If your collection was called Markets, the code would look like:
var market = Markets.findOne({market: 'AAA'}, {sort: {creationDate:-1}});
Markets.update(market._id, {$set: {fancy: true}});
It's worth mentioning that even if MongoDB supported the optimization you are looking for, meteor client code can only update by _id anyway.
Related
I have a firestore collection with a bunch of documents, each with plenty subfields. On a web page I need a list of a specific subfields from each document.
Currently I load the the entire database when you load the page and then loop through and get the wanted values. This uses way to many reads to get very little data.
Is there a way to solve this e.g. a autogenerated a collection that contains field from other collection in an array or something.
Many thanks in advance
Auto-creating such a subcollection with just the fields you need is a great way to reduce the bandwidth needed to load the data.
There is nothing built into Firestore to create those derived documents, but it's fairly easy to build something using Cloud Functions. Create a function that responds to a Firestore onWrite trigger, and write the subset of the data to its destination there. It's common to have a separate Cloud Function for each such use-case, and I regularly see projects with 100+ such functions.
I expect we'll also start seeing Firebase Extensions for this type of thing, but right now no-one seems to have built one.
exist any way to know if this function collects information from an accesible collection?
For example these registres:
db.currentOp(true).inprog.forEach(function(d){if(d.client)print(d.client, d.connectionId)})
I was looking at the data in the 'oplog.rs' collection but it didn't seem contain what I am looking for.
There's no database collection mentioned in the documentation which means that currentOps are most likely held in an internal MongoDB data structure.
Browsing the github MongoDB repository and the body of currentOp method leads to CurOp C++ class which is simple in-memory stack implementation so there's no persistent storage for current ops.
You can also take a look at system.profile if you're trying to build some sort of diagnostic solution which requires persistent storage.
I want to store the comma separated ids on a child node & how can I filter data as in sql we can use IN clause to fetch data any possibility in firebase to perform this kind of operation in firebase database.
Please suggest any possible solution for this.
Firebase Realtime Database doesn't have the equivalent of SQLs IN clause. It also doesn't have a way to find a substring in a value. So the data model you are looking to use, doesn't allow the use-case you want. As usual with NoSQL databases, the solution is to pick a data model that does allow your use-case..
The most likely cause I know for the structure you describe is to associate the child node with a bunch of categories. If that is your case, read my answer here for a proper data structure: Firebase query if child of child contains a value
This is one of the cases where the new Cloud Firestore database offers better querying support, since it recently added a feature to efficiently test if an array contains a certain value (video). If you're only just getting started with your project, you might want to check if Firestore is a better fit for your use-cases.
plnkr
I am trying to traverse through a collection, and update each document respectively.
My UserProfile collection consists of multiple JSON objects of userProfiles. As you can see, each profile has a lot of the same information. The only difference is the personal information. (This is just a test case of hard coded objects. The real data will be in an SQL DB managed by a sysadmin).
What I am trying to do is write a function (replaceTopics) that will take in an array of topics and replace each topic that matches in the collection. So if the system admin makes a change to a topic/s, he will send me the topic/s and I will be checking each document in my userProfile collection to see if that document has the matching topic (by matching topicIDs), if so, I need to replace that entire topic with the editedTopic.
I have tried this but with no luck. You can take a look at my function.
well, i am creating a network that allows users creating posts and like them.
Asking on stackoverflow i've understood how to structure my database:
A collection which includes a document for each post.
A collection which includes a document for each like, in each of these documents there is a reference to post is referenced to.
When i want to get ALL likes about a post i can query the like collection looking for the reference to that post.
And till here i am ok. But assuming i'll have millions documents in like collection, i wondered how could i query and search among them in not too long time.
And i was advised of ensureIndex, in this case, i have to ensureindex of the field which contains reference to a post.
But when do i have to create this index? is enough to create it once (for example when i set up my database) and it will be as default in mongodb or do i have to do it during application life-time? thank you
But assuming i'll have millions documents in like collection, i wondered how could i query and search among them in not too long time.
I assume you would most likely want to do a count on the likes as an example?
You can't, instead you use optimizations to combat this. A count on millions of rows might get a bit slow.
A typical scenario are counters in SQL techs that you use to amend the parent row with a sum figure of its children.
Same applies to MongoDB.
You would aggregate important data to the top.
If you require to actually query the likes to show some who have liked it then you limit those likes. Google+ and other networks tend to limit the amount of likes they show to about 1,000.
And i was advised of ensureIndex,
Adding indexes to a database does help with actually searching for documents.
But when do i have to create this index? is enough to create it once
Yes, MongoDB will manage the index itself. You only need to ensure it once.