How to get Post with Comments Count in single query with CouchDB?
I can use map-reduce to build standalone view [{key: post_id, value: comments_count}] but then I had to hit DB twice - one query to get the post, another to get comments_count.
There's also another way (Rails does this) - count comments manually, on the application server and save it in comment_count attribute of the post. But then we need to update the whole post document every time a new comment added or deleted.
It seems to me that CouchDB is not tuned for such a way, unlike RDBMS when we can update only the comment_count attribute in CouchDB we are forced to update the whole post document.
Maybe there's another way to do it?
Thanks.
The view's return json includes the document count as 'total_rows', so you don't need to compute anything yourself, just emit all the documents you want counted.
{"total_rows":3,"offset":0,"rows":[
{"id":...,"key":...,value:doc1},
{"id":...,"key":...,value:doc2},
{"id":...,"key":...,value:doc3}]
}
Related
HI I'm new to cloudant (and couch and asking questions on stackoverflow so I hope I manage to be vaguely clear about what I'm asking ) and I'm trying to do probably the second most basic geo task but am hitting a dead end.
I've got a database of docs which are geojson objects, I've created an index so I can query for intersections etc but it seems the only options I have in the url is the format=legacy (gives me the ids) and the format=geojson and the include_docs parameter - what I'd like to do is give back a particular view of the result set - I'm not interested in the geometry of the object (which is a big lump of data and it's likely that a number of other properties may be in the document that I'd rather filter out)
is there a correct way to do this in a single api call or do I need to fetch the doc ids (legacy format) and then issue a second query to bring back my chosen 'view' for each document id given in the result of format=legacy response
Thanks
I am working on a node.js app, and I've been searching for a way around using the Model.save() function because I will want to save many documents at the same time, so it would be a waste of network and processing doing it one by one.
I found a way to bulk insert. However, my model has two properties that makes them unique, an ID and a HASH (I am getting this info from an API, so I believe I need these two informations to make a document unique), so, I wanted that if I get an already existing object it would be updated instead of inserted into the schema.
Is there any way to do that? I was reading something about making concurrent calls to save the objects, using Q, however I still think this would generate an unwanted load on the Mongo server, wouldn't it? Does Mongo or Mongoose have a method to bulk insert or update like it does with insert?
Thanks in advance
I think you are looking for the Bulk.find(<query>).upsert().update(<update>) function.
You can use it this way:
bulk = db.yourCollection.initializeUnorderedBulkOp();
for (<your for statement>) {
bulk.find({ID: <your id>, HASH: <your hash>}).upsert().update({<your update fields>});
}
bulk.execute(<your callback>)
For each document, it will look for a document matching the {ID: <your id>, HASH: {your hash}} criteria. Then:
If it finds one, it will update that document using {<your update fields>}
Otherwise, it will create a new document
As you need, it will not make a connection to the mongo server on each iteration of the for loop. Instead a single call will be made on the bulk.execute() line.
In past with my PHP / Rails - MYSQL apps I've used the unique ID of a table record to keep track of a record in an html file.
So I'd keep track of how to delete a record shown like this (15 being the ID of the record):
Delete this record
So now I'm using MongoDB. I've tried the same method but the objectID ._id attribute seems to be a loooong byte string that I can't use conveniently.
What's the most sensible way of binding a link in the view to a record (for deletion, or other purposes or whatever)?
If the answer is to create a new id that's unique for each document in the collection, then what's the best way to generate those unique id's?
Thank you.
You could use a counter instead of the ObjectID
But this could create a problem when inserting a new document after you deleted a previous one.
See this blog post for more detail info on Sequential unique identifiers with Node.js and MongoDB.
Or you could use the timestamp part of the ObjectID:
objectId.getTimestamp().toString()
See the node objectid docs
I want to delete all documents where foo equals x. Seems like a pretty basic operation, but I just can't figure it out.
I know how to delete an individual document, but that's not good enough - I may have to delete a few thousand at a time.
How do I bulk delete documents in CouchDB?
I don't know if it's the right way but make a view that exposes the foo field, query the view for the doc._ids of all your documents that you want to delete, and make a bulk update against all your documents. So two (ideally) calls to couch.
http://comments.gmane.org/gmane.comp.db.couchdb.user/11222
Has a similar way to go about it.
Do a bulk update on all the documents you want to delete and update doc._deleted=true following the example in Bulk deletion of documents
It's quite easy with bulk delete: https://wiki.apache.org/couchdb/HTTP_Bulk_Document_API
Just POST to _all_docs a list of JSONs that look like:
{"_id": "0", "_rev": "1-62657917", "_deleted": true}
I also needed something to handle that and, since there was nothing at the time, I decided to make my own implementation.
You can find it here.
Update
Since it was very helpful to me and in order to protect myself from mistakes, I added a backup/restore feature to this tool that can now be found on version 0.2
I tried a somewhat long method to delete documents. I first created a view called map_fun that called the documents i wanted to get deleted. I then iterated through the view and stored the keys of allt he documents and used del db['_id'] to delete them
map_fun = function(doc){
if (doc.doc_type == 'classic'){
emit(doc._id, doc)
}}
deldoclist = []
for row in db.query(map_fun):
deldoclist.append(row.key)
for item in deldoclist:
del db[item]
How can I get last created document in couchdb? Maybe some how I can use _changes feature of couchdb? But documentation says, that I only can get list of document, ordered by first created document, ant there is no way to change order.
So how can I get last created document?
You can get the changes feed in descending order as it's also a view.
GET /dbname/_changes?descending=true
You can use limit= as well, so;
GET /dbname/_changes?descending=true&limit=1
will give the latest update.
Your only surefire way to get the last created document is to include a timestamp (created_at or something) with your document. From there, you just need a simple view to output all the docs by their creation date.
I was going to suggest using the last_seq information from the database, but the sequence number changes with every single write, and replication also complicates the matter further.