I see this has been discussed previously (here:Retrieve just deleted document) but I am having some trouble understanding.
Given I have a database named "test" running on IP address 127.0.0.1:5984, and a document with the ID "xyz123":
Get all the revisions of the deleted document with the following request:
$db/$id?revs=true&open_revs=all
Where $db is your CouchDB database name and $id is your deleted document id.
Does this mean:
GET http://127.0.0.1:5984/test/"xyz123"?revs=true&open_revs=all ??
I am not sure of the correct syntax for submitting "$id".
The id becomes part of the URL, no quoting necessary. Your example call would be GET http://127.0.0.1:5984/test/xyz123?revs=true&open_revs=all.
For reference, the documents API area has some basic id examples.
Related
I am looking for a workaround for primary key feature in couchdb. I am saving doc in json format to couchdb externally. Is there any simple way to check if value of a particular field exists?
If you try to save a document that already exists, it will be rejected unless the revision is set to match the existing revision.
Alternately, you can just try to fetch the document, either with GET or HEAD, to check if it exists. See the relevant documentation.
You could perform a mango query previous to the document creation but it will not warranty that another process create a document between the check and the creation.
This post discusses about the same issue:
How to check for duplication before creating a new document in CouchDB/Cloudant?
I've never worked with a database before, but I chose Couch DB because I needed a Json database, and HTTP queries seemed kinda simple. However the documentation assumes a level of knowledge I just don't have.
Assuming I have a database called 'subjects', it seems I can access the json by using GET on
http://localhost:5984/subjects/c6604f65029f1a6a5d565da029001f4c
However beyond that I'm stuck. Ideally I want to be able to:
Access a list of all the keys in the database (not their values)
Access an individual element by its key
Do I need to use views for this? Or can I just set fields in my GET request? Can someone give me a complete example of the request they'd use? Please don't link to the CouchDB documentation, it really hasn't helped me so far.
Views can be used to fetch the data
1) In order to get all keys from the database you can use below view
function(doc) {
if (doc.type=="article")
emit(doc._id,null); //emit(key,value), if you have any other field as key then specify as doc.key e.g doc.
}
You can access this view from browser using below URL
http://<ipaddress>:<port>/databasename/_design/designdocumentname/_view/viewname
e.g :
http://<ipaddress>:<port>/article/_design/articlelist/_view/articlelist
article is the database name,articlelist is name of the design document as well as view.
2) In order to access individual document by key
Below view will return all the articles belonging to a particular department
function(doc) {
if(doc.type == 'article' ) {
emit([doc.departmentname], doc);
}
}
Query this view based on the "department name"
e.g: Get all the articles belonging to "IBU3" department
http://<ipaddress>:<port>/department/_design/categoryname/_view/categoryname?key=[%22IBU3%22]
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 really like the document-based approach of storing data like blog posts as a whole document with all information needed saved inside of it. Therefore the author´s username is stored as plain text. The author himself has his own document with personal information attached to it. What happens when the author decides to change his username? Do I have to update every document the contains a blog post by that author or is this just one of the drawbacks using a document-based database?
Thanks for any suggestions!
If you need to write a query(view) with content from the blogpost and the name of the author, then the name must be included in the blog content, and therefore all blogposts must be updated.
if the name is only for information ( i mean you do not query a blogpost-content like keywords AND name of author), you can add the id into the blog document (and of course now can Query blog content AND author-id) and emit {'_id':doc.author_id} as a Value.
include_docs=true then gives you the doc of the Author (and no longer the blogpost-doc.. you have to call it explicit with the id thats in the result rows). No Need to update the blogposts.
Example:
Case 1:
Use Author by Name, you have to include the name, and therefore update ALL docs.
{
"_id":"blogpost1",
"author":"Oliver",
"keyword":"couchDB"
}
to look for all couchdb posts from oliver:
emit ([doc.author,doc.keyword],1)
call:
&key=["Oliver","couchDB"]
Case 2:
No need to query by name
{
"_id":"blogpost1",
"author_id":"author-123",
"keyword":"couchDB"
}
emit (doc.keyword,{'_id':doc.author_id})
and the authors doc:
{
"_id":"author-123",
"name":"Oliver"
}
call:
?key=["couchDB"]&include_docs=true
result:
...
{"id":"blogpost1","key":"couchDB","value":{"_id":"author-123"},"doc":{"_id":"author-123","_rev":"xxx","name":"Oliver,....
I've come to really love the couchdb style of organizing and updating data, but there are a few situations where I really need to be able to create an entry and determine if an equivalent entry is already in existence before returning to the user. The only situation that this is absolutely necessary for my application is user registration. I'm fine with having all user registration writes go to a particular, designated couchdb instance known as the "registration-instance".
I want to hash the user_id into some _id to use. Then execute a put with this _id, but fail if the _id is already inserted. I need to return to the user that the user name is already reserved, and I cannot detect the conflict later and resolve it at that point, because the user would be under the impression that they had reserved the user name.
I don't see why couchdb couldn't provide some way to do this, under the assumption that you designate that inserts for a particular "type" of document always are routed to a particular instance.
If you send a single CouchDB server a PUT request for a new user document you should get the behavior you want already.
If the document does not exist then it will create the new document.
If the document does exist then it is guaranteed to return a 409 conflict error. This is due to the fact that you did not supply a _rev property because you aren't trying to update the pre-existing document.
Only when the _id and _rev properties match will CouchDB update the existing document.
You might also want to read up on document update handlers:
http://wiki.apache.org/couchdb/Document_Update_Handlers
You might use an update handler to hash the user_id and dynamically assign the appropriate _id. You can also customize what kind of error response couch sends with an update handler.
Good luck!