As a CouchDB beginner I'm having a hard time understanding how to update documents.
When I read the docs I find this which is quite confusing for me:
1) Updating an Existing Document
To update an existing document you must specify the current revision number within the _rev parameter.
Source: Chapter 10.4.1 /db/doc
2) Update Functions
Update handlers are functions that clients can request to invoke server-side logic that will create or update a document.
Source: Chapter 6.1.4 Design Documents
Could you please tell me which way do you prefer to update your documents?
Edit 1:
Let's say the data structure is just a simple car document with some basic fields.
{
"_id": "123",
"name": "911",
"brand": "Porsche",
"maxHP": "100",
"owner": "Lorna"
}
Now the owner changes, would you still use option 1? Option 1 has quite a downside, because I can't just edit one field. I need to retrieve every fields first, edit just the owner field and than send back the whole document. I just tried it and I find this quite long-winded. Hmmm...
Most of the time you want to choose option 1 "Update an existing document"; this operates on a standard document that stores data in the database. The other option relates to design documents, such as views (which are also documents, this is definitely confusing to new CouchDB users), which is something completely different.
Stick with option 1, and good luck :)
Related
I'm a noobie in Nodejs and MongoDb so please excuse my silly doubts :D but i need help right now
{
"_id": "someid",
"data": "some_data",
"subData": [
{
"_id": "someid",
"data": "some_data"
},
{
"_id": "some_id",
"data": "some_data"
}
]
}
I have a schema like above and imagine i have millions of Documents in that schema, Now i want to update those Documents.
Based on condition i want to select a set of them and modify those "subdata" arrays and update them.
I know there is no way to do that in one query and the issue here at Jira for that feauture but my question now is, what is the most efficient way to update a million records in mongoDb ?
Thanks in advance :)
Going by the schema that you have posted here, it is good that you are maintaining a specific id for the sub document which is automatically added if you are using mongoose (in case the backend is node.js).
I would like to post something from the post that you have posted along with the main post of yours.
It doesn't just not work for updating multiple items in one
array, it also doesn't work for updating a single item in an array for
multiple documents.
So our relevant option there goes out of the window. There is no way to update large chunks in single command as you'll have to target them individually.
If you are going to target them individually it is advisable that you target them using specific unique ids that are being generated and now to automate the whole process you can choose whichever efficient method suits the backend you are using.
You can make several processes in parallel that would help you to attain the desired task in less time but it wont be possible to do everything in one go because mongodb don't support that.
It is also advisable that at place of maintaining several sub documents you should just go for separate collection instead as it'll ease the whole process. Maintain a field to map your two collections.
References
https://jira.mongodb.org/browse/SERVER-831
https://jira.mongodb.org/browse/SERVER-1243
https://www.nodechef.com/docs/cloud-search/updates-documents-nested-in-arrays
I have an issue of replication and I need your help in it.In couchDb replication,I want to replicate in such a way that during Couchdb replication I want to reset/update some specific attributes of a a document for some purpose and then these edited documents should be saved in replicated db without effecting the original ones.For example:
A document named Student with attributes id,name,class etc.
And I want to replicate this document in the way that its name and class should be reset/updated.
Will you please tell me how can I achieve it.
Thanks.
You can't update docs during the replication.
But you can exclude docs from being replicated with the help of a CouchDB filter (e.g. preventing all docs with a revision higher then 1 from being replicated).
If you want to have multiple versions of the same dataset (e.g. to have dataset revisions) - i use the term "dataset" instead of "doc" to clearly express that not the internal CouchDB doc revision handling is involved - you have to store them as separated docs that have all a unique id and a reference property like original: "UUID_of_the_original".
you can't use the CouchDB doc revision handling for that purpose (thats what many people think when they see the _rev property in the docs)
Basic problem
I have some large, but logically organised documents - and would like to perform updates on just a sub-section of an individual document.
Example
Given this simple document:
_id: 123456,
_rev: 3242342,
name: 'Stephen',
type: 'Person',
hobbies: [ 'sky-diving' ]
In my application I might have an addHobbies method, that would use a view that just retrieves:
_id: 123456,
_rev: 3242342,
hobbies: [ 'sky-diving' ]
So that it can then add an additional hobby to the hobbies array, and then PUT just this sub-set of data back to the document.
Question
As I understand it, CouchDB [1.2] does not allow partial updates like this, and so I believe it would be necessary to grab the whole document during the save operation, merge my changes, then PUT the whole document back on every single save.
Is there another way of doing this (am I wrong about CouchDB's capabilities)?
Are there any libraries (I'm using express on node.js) to handle this kind of operation?
You are correct. That is, in fact, what document database means: check-outs and check-ins.
You can create (or use) shim code to simulate what you want, letting you focus on the important parts. On the server side, you can use update functions.
There are many solutions on the client side.
cradle.js will give you fake partials updates with the merge method.
If you only want to update one or more attributes, and leave the others untouched, you can use the merge() method:
db.merge('luke', {jedi: true}, function (err, res) {
// Luke is now a jedi,
// but remains on the dark side of the force.
});
https://github.com/cloudhead/cradle/
Related, and also for Node.js is Transaction for performing arbitrary atomic transactions on CouchDB documents.
I would say that cradle is currently missing a real partial update feature, which would also support updating a path to a key inside the field value's JSON data, like Apache demonstrates here, rather than being limited to updating only a single key in a document, like the db.merge method.
In fact, looking at the cradle source, I see that there is a Database.prototype.update method (in lib/cradle/document.js), but this method doesn't seem to be documented.
It would be elegant of this could be made an integral part of cradle, eliminating the need to do separate requests to CouchDB view's updates only for partial updates.
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]
Is it possible to have couch update or change fields on the fly when you create/update a doc? For example in the design view.... validate_doc_update:
function(newDoc, oldDoc, userCtx) {
}
Within that function I can throw errors like:
if(!newDoc.user_email && !newDoc.user_name && !newDoc.user_password){
throw({forbidden : 'all fields required'});
}
My Question is how would I reassign a field? I tried this:
newDoc.user_password ="changed";
with changed being some new value or hashed value. My overall goal is to build a user registration/login system with node and couchdb and have not found very good examples.
The validate_doc_update function cannot have any side effects and cannot change the document before storage. It only has the power to block an update or to let it through. This is important, because the function is not only called when a user requests an update, but also when changes are replicated from one CouchDB instance to another. So the function can be called multiple times for one document.
However, CouchDB now supports Document Update Handlers that can modify a document or even build it from scratch. These can be used to convert non-JSON input data into usable documents. You can find some documentation in the CouchDB Wiki.
Before you build your own user registration/login system, I'd suggest you look into the built-in CouchDB security features (if you haven't - some information here). They might not be enough for you (e.g. if you need email validation or something similar), but maybe you can build on them.