StorIOSQLite has interesting method observeChangesInTable(). And When I saw it I thought that it would observe changes in given table and return list of updated items.
But it just returns updated table name. Why would I need an updated table name? I can just subscribe to hole table to be notified about an update
storIoSqLite.get()
.listOfObjects(Item.class)
.withQuery(
Query.builder()
.table(ItemTable.NAME)
.build()
)
.prepare()
.asRxObservable()
Please explain what is the point of observeChangesInTable() method. And what is the best solution for my problem.
With your approach you're actually doing a query to the db and only then reacting to the change.
With StorIOSQLite.observeChangesInTable() you can react on changes in the table without doing any queries to the db. This is much much cheaper and should be used in situations when you need to do a debounce() or window(), filter() etc and only then make actual query to the db.
Hope that helps!
Related
I would like to get all the docs in couchDb updated in a specific time range.
I'm using the below API but I don't get any result.
/_all_docs?startkey="2019-01-01T00:00:00Z"&endkey="2020-01-01T00:00:00Z"
Any suggestions are welcome.
Andrea
_all_docs's key is the document ID, not timestamp. For your query to be useful, you'll need to create a custom view based on a timestamp (and ensure the timestamp is updated by your code).
I want to store information in some activities that are modified versions of activities imported from an existing database (ecoinvent).
I know we can add fields to activities created from scratch (example). (I guess this is because the structure of the database has not yet been defined...) but is there a way of adding it to activities of an already defined database without breaking it?
The way around I found is to add entries to the author dict, which I can easily access later on. e.g.
act['author']['scenario']='myscenario'
but I admit it is not a very elegant solution.
You can just add whatever data you want. Brightway is a (semi-)schemaless database for exactly this reason.
act['foo'] = 'bar'
act.save()
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.
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}]
}
I'm using haystack with whoosh for development purposes.
I want search results based on django models to be filtered by the user that created them.
Please see my other post Filter haystack result with SearchQuerySet for details.
Basically I had to add User to my search index. But I noticed, when I manually change the user_id of a record, search is broken. After thinking about it this even makes sense. But, this means I have to rebuild the index after each field update in each model? Surely that doesn't scale at all?
I thought the engine would find the object by id, then look it up in the database, and return a current instance for further processing like filtering. It seems like everything is cached in the index so must be synchronized in realtime for search results to show up? Am I missing something here?
This documentation helped shed some light:
http://docs.haystacksearch.org/dev/searchindex_api.html