How can I write the serverValue.timestamp() as a separate child in Firebase?
I want to be able to write something like this:
-Country
---Location
------serverValue.timestamp()
---------Name: Peter
---------Age: 30
---------Class: Physics
When I try this it fails:
self.ref?.child(country).child(location).child(serverValue.timestamp()).updateChildValues(["Name:" : name, "Age:" : age, "Class:" : class])
I can't seem to get it right...
According to the docs timeStamp is a placeholder for a value in which the database recognize and put in the current servertime. This does not apply for Strings in the database. Strings in the databases are names for folders, documents, collections, keys etc. So the method you are calling only works for a value in combination with a key, for storing data in JSON format.
If you REALLY want to use the current timestamp without users faking the current time, I think the only thing you can do is:
write the data to a temp folder
trigger a Cloud Function that listens to that folder/document
write the data back to your preferred folder/document, while the name of the folder/document is Date.now() (function in javascript)
Else you could always use Swift's current timestamp: How to get 18-digit current timestamp in Swift?
Related
We are evaluating NEsper. Our focus is to monitor data quality in an enterprise context. In an application we are going to log every change on a lot of fields - for example in an "order". So we have fields like
Consignee name
Consignee street
Orderdate
....and a lot of more fields. As you can imagine the log files are going to grow big.
Because the data is sent by different customers and is imported in the application, we want to analyze how many (and which) fields are updated from "no value" to "a value" (just as an example).
I tried to build a test case with just with the fields
order reference
fieldname
fieldvalue
For my test cases I added two statements with context-information. The first one should just count the changes in general per order:
epService.EPAdministrator.CreateEPL("create context RefContext partition by Ref from LogEvent");
var userChanges = epService.EPAdministrator.CreateEPL("context RefContext select count(*) as x, context.key1 as Ref from LogEvent");
The second statement should count updates from "no value" to "a value":
epService.EPAdministrator.CreateEPL("create context FieldAndRefContext partition by Ref,Fieldname from LogEvent");
var countOfDataInput = epService.EPAdministrator.CreateEPL("context FieldAndRefContext SELECT context.key1 as Ref, context.key2 as Fieldname,count(*) as x from pattern[every (a=LogEvent(Value = '') -> b=LogEvent(Value != ''))]");
To read the test-logfile I use the csvInputAdapter:
CSVInputAdapterSpec csvSpec = new CSVInputAdapterSpec(ais, "LogEvent");
csvInputAdapter = new CSVInputAdapter(epService.Container, epService, csvSpec);
csvInputAdapter.Start();
I do not want to use the update listener, because I am interested only in the result of all events (probably this is not possible and this is my failure).
So after reading the csv (csvInputAdapter.Start() returns) I read all events, which are stored in the statements NewEvents-Stream.
Using 10 Entries in the CSV-File everything works fine. Using 1 Million lines it takes way to long. I tried without EPL-Statement (so just the CSV import) - it took about 5sec. With the first statement (not the complex pattern statement) I always stop after 20 minutes - so I am not sure how long it would take.
Then I changed my EPL of the first statement: I introduce a group by instead of the context.
select Ref,count(*) as x from LogEvent group by Ref
Now it is really fast - but I do not have any results in my NewEvents Stream after the CSVInputAdapter comes back...
My questions:
Is the way I want to use NEsper a supported use case or is this the root cause of my failure?
If this is a valid use case: Where is my mistake? How can I get the results I want in a performant way?
Why are there no NewEvents in my EPL-statement when using "group by" instead of "context"?
To 1), yes
To 2) this is valid, your EPL design is probably a little inefficient. You would want to understand how patterns work, by using filter indexes and index entries, which are more expensive to create but are extremely fast at discarding unneeded events.
Read:
http://esper.espertech.com/release-7.1.0/esper-reference/html_single/index.html#processingmodel_indexes_filterindexes and also
http://esper.espertech.com/release-7.1.0/esper-reference/html_single/index.html#pattern-walkthrough
Try the "previous" perhaps. Measure performance for each statement separately.
Also I don't think the CSV adapter is optimized for processing a large file. I think CSV may not stream.
To 3) check your code? Don't use CSV file for large stuff. Make sure a listener is attached.
I have a large query running on a collection pulling back the date in NumberLong format, I then export to a .csv where I run a formula to convert the date to a format a human can use. Scrolling the web I am not able to find a clear way of pulling the date in 'YYY-MM-DD' format and not the NumberLong on the fly. Has anyone managed this?
If you are doing this as a once off action, one way of doing this is to use the forEach() method to convert the date and inject the new converted object into a temporary collection. Then dump that collection to CSV.
Something like this:
db.myCollection.find().forEach(function(element) {
element.dateField = new Date(element.dateField);
db.myTempCollection.insert(element);
});
Otherwise, I recommend using your programming language of choice and implementing a program or script to do the conversion.
I am now building an iPhone app and it involves core data. One of the entities has an attribute with Date type, which effectively generates a column with TIMESTAMP type in the corresponding sqlite DB. The value looks something like 320928592.400471
My question is... how can I convert ordinary datetime into the TIMESTAMP type? I would like to preload some static data to the DB. Therefore, I need to know how to store the data directly to the DB.
Chances are that number is the same number returned by NSDate's timeIntervalSinceReferenceDate, i.e. seconds since 1 January 2001.
It might be easier to either populate the database on the first run of your program, or to generate the prefilled database and export it from your phone to include in the bundle.
I would like to write a function module that returns a range table. Is that possible and if so, how?
The structure of a typed range is like this :
**Name** **Type**
SIGNT VARV_SIGN
OPTION TVARV_OPTI
LOW your-type
HIGH your-type
You can create this structure in the dictionary, as well as a table of those, and then use it in the FM signature.
Also, a generic structure already exists : RSDSSELOPT (along with a table type RSELOPTION).
This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google.
I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row.
There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these).
It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database.
First, a quick threshold question of, is this a good idea? Any feedback or anything I missed?
Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?
If you're finding that you need to change the display values, then yes, it's probably a good idea not to store them in a database. Integers are also more efficient to store and search, but I really wouldn't worry about it unless you've got millions of rows.
You just need to run an update to populate your new column:
update table_name set content_type = (case when old_content_type = 'a' then 1
when old_content_type = 'b' then 2 else 3 end);
If you're on Postgres 8.4 then using an enum type instead of a plain integer might be a good idea.
Ideally you'd have these fields referring to a table containing the definitions of type. This should be via a foreign key constraint. This way you know that your database is clean and has no invalid values (i.e. referential integrity).
There are many ways to handle this:
Having a table for each field that can contain a number of values (i.e. like an enum) is the most obvious - but it breaks down when you have a table that requires many attributes.
You can use the Entity-attribute-value model, but beware that this is too easy to abuse and cause problems when things grow.
You can use, or refer to my implementation solution PET (Parameter Enumeration Tables). This is a half way house between between 1 & 2.