How do I write a mongodb query in iReport to fetch data from previous record?
Example,
I have 3 columns - start,end,rest.
'Rest' has to be calculated as the difference between start of one record and the end of previous record. ('start' and 'end' are dates)
There are a few ways to do this. Basically you have to rework the data in the query so that it has the right format when it is about to be printed in JasperReport. This can be accomplished with runCommand command or mapreduce command given that you have sufficient permissions. Your best option is probably mapreduce. I suppose you have read this reference.
Related
My transformation starts with a Table input step with a query that retrieves a value from a table column (named ID_EXECUCAO).
I want to search my MongoDB Collection filtering by this value, using the function $match on my MongoDB input step query.
I know I can search by a parameter using "${PARAMETER}", but how do I search by a value passed from a previous step?
I tried this way and it doesn't work:
$match: {
"IdExecucao": $ID_EXECUCAO
}
I sure that you can't do it by get data from previous step like 'Table Input Step'. No option 'Insert data from step' in MongoDB Input.
As you known, the only way is to use Variable (${VARIABLE_NAME}).
Is there a simple OR elegant method (or query that I can write) to retrieve the last updated timestamp (of the last updated document) in a collection. I can write a query like this to find the last inserted document
db.collection.find().limit(1).sort({$natural:-1})
but I need information about the last updated document (it could be an insert or an update).
I know that one way is to query the oplog collection for the last record from a collection. But it seems like an expensive operation given the fact that oplog could be of very large size (also not trustworthy as it is a capped collection). Is there a better way to do this?
Thanks!
You could get the last insert time same way you mentioned in the question:
db.collection.find().sort({'_id': -1}).limit(1)
But, There isn't any good way to see the last update/delete time. But, If you are using replica sets you could get that from the oplog.
Or, you could add new field in document as 'lastModified'.
You can also checkout collection-hooks. I hope this will help
One way to go about it is to have a field that holds the time of last update. You can name it updatedAt. Every time you make an update to the document, you'll just update the value to the current time. If you use the ISO format to store the time, you'll be able to sort without issues (that's what I use).
The other way is the _id field.
Method 1
db.collection.find().limit(1).sort({updatedAt: -1})
Method 2
db.collection.find().limit(1).sort({_id: -1})
You can try with ,
db.collection.findOne().sort({$natural:-1}).limit(1);
I have a map/reduce that I noticed was taking nearly 10 seconds to run, even though no results were being returned. Using the mongo shell, I was able to determine that my initial query was the culprit. I was able to add a 2nd sort field to the query, which sped it up drastically.
However, when I try to add that 2nd sort field to my map reduce, I get the error "could not create cursor over [collection] for query ...". Is there any way for me to add a 2nd sort field to the map reduce?
Edit: The goal of my query is to find the first record created by each user/day. So the key that I am emitting is the user's id + created on day, ignoring any time. That way I am grouping all records created by a user on a given day. In my reduce, I am then taking the record that was created first. I have actually ditched using map/reduce and am now doing essentially the same thing, but with a normal find() and then some javascript to group and reduce.
I have a mongodb query, and I want to add a computed field. The computed field is based on where or not the item is in the results of another query. So my query returns the columns a,b,c,d, and then column e should be based on whether or not the current row would be matched by another query.
Is there an efficient way to do this in mongo? I'm not really sure how to do this one...
There is no way currently to execute a function as you describe within the database when returning a document via standard functions such as find. It's been requested by the community, but the general request is to operate only on a single document.
There are calculated fields using $project in the aggregation framework. But, they only operate on the current document in the pipeline. So, they can't summarize other queries.
You'll need to likely build your e value as part of your data access layer.
I have 10000 documents in one MongoDB collection. I'd like to update all the documents with datetime values that are 1 second apart for each document (so all the date time values are unique and are spaced 1 second apart). Is there any way to do this with a single update instead of updating each document in turn which results in 10000 distinct update operations?
Thanks.
No, there is no way to do this with a single update statement. There are no expressions which run at the server to allow this type of update. There is a feature request for this but it is not done so it cannot be used.