I kind of understand what DynamicView is. However, at the same time, I am confused by what it really means.
I know how to use it based on articles I have read such as here. However, what is it?
Imagine you have a db, you run a query like "give me all the users that are marked as logged in". You obtain that result back and you process it for the purposes of your application. If you run that same query at a different time, you get a different result set.
In LokiJS, Collections are event emitters, and Dynamic Views are registered to listen to those events. Which means they are aware of the changes that occurred in the Collection, and they apply it to the result set of the view. In the above case, if you create a Dynamic View, whenever you call data() you get the result corresponding to the current status of the database, not when the view was created. You run a query once, and you can forget about updating its results, the Dynamic View does that for you (through the data() method, which is lazy).
This can be very helpful - but it also prevents you from storing a history of states in your application, so use with caution!
The correct definition for a dynamic view is self-materializing view.
Related
In moodle,I could see the default course progress for the courses in the moodle on the front end. But when tried to show the progress like 10% completed when chapter1 gets completed, 20% completed when chapter2 gets completed and so on. I could not find any module or could not figure out how to modify the code.
In other words:1. How to track the progress of course completion based on course subsections completion? Because default tracking based on courses based only.2. It is possible to track the courses without (refer https://i.stack.imgur.com/GUqwT.png) ticking the course completion checkbox?3. Based on the URL viewing of course sections, is it possible to track the course progress?Thanks in advance.
You can sometimes track specific page views and interactions via the mdl_logstore_standard_log table. Different modules/activities in Moodle log different types/amounts of data, but views of typical course topics/sections are usually logged regardless of completion.
For example, imagine a course with id=10 where you visit section/topic 3. The URL usually looks something like this: <yourdomain>/course/view.php?id=10§ion=3
In this case, the view should be logged in mdl_logstore_standard_log with an eventname value of \core\event\course_viewed. The course id should be in the courseid column and the section viewed should be in the "other" column, although that data is an array stored with PHP serialization, so it's helpful to use unserialize and array parsing functions to get the "3" quickly if needed.
Again, keep in mind different activities/modules log data differently - for example, an assignment activity is logged differently - but hope this helps you find what you need. Good luck!
I have a view over a table. It turns out the table gets moved and an updated version of it created each night. This ensures there is always a table of the expected name present in the database, but I cannot find a way to make my view continue to point to the current version of the table. Whichever table existed when the view was created is the one I end up pointing to even after it moves and goes stale.
ViewA:
select a, b, c from todays_table;
todays_table stays current all day, then at night it gets renamed to todays_table01. View A now points to todays_table01 and a new table shows up called todays_table. Again, todays_table is current, but ViewA no longer is.
Is there a way to delay the table name resolution until the view is used? I haven't been able to get EXECUTE IMMEDIATE working for SELECT statement. I think I could get a dynamic SQL statement working if I used a cursor, but I have never needed these before and I'm not sure if they are the right path. I read about AUTO_REVAL but I believe this would only delay resolution until the first time the view was used and still go stale that night.
I could, of course, stop using the view and just move the complex query into my program but there are many places it is needed so I would like to eliminate all other solutions before falling back to this.
It would be ideal to eliminate the temporary table and just have the master table receive updates throughout the day but this is beyond my comprehension as I know nothing about RPG II and OCL.
Thanks for reading.
Edit
Per #Mr. Llama's suggestion, I experimented with using synonyms and aliases to point to todays_table and then having my view point to the synonym. Unfortunately in this scenario, the view uses the alias to resolve the actual table name on creation so the view continues to point to todays_table when it is renamed to todays_table01, though the alias continues to reference todays_table.
Edit 2
I'm accepting #mustaccio's answer because it does work and would be a reasonable approach to this problem if I could get the parameters going where they need to. My particular project requires flexibility so I am actually going to jump on the nightly process bandwagon and add a program to recreate my views after the process messes with their references as #danny117 suggested.
Thanks to everyone who replied though, I learned a lot about how all of these pieces work together.
I think you might be able to achieve what you want by wrapping your view definition in a SQL table function, something like
CREATE FUNCTION insteadofview (<parameters>)
RETURNS TABLE (<columns>)
...
RETURN
SELECT <the rest of your view definition>
Depending on how you query your view, you will probably need to pass search criteria into the function as parameters, otherwise performance will be suboptimal because the function will have to return all rows from the query before search arguments can be applied.
According to the manual, as you have noticed views on a table that is renamed continue to point to the original table object. Routines, however, including table functions, will be invalidated and their plans prepared again when they next invoked, using the original source table name.
I have no way of testing this though.
Full syntax to create a table function.
My question is clear as in the title. When a request come to my service for updating related record in mongoDb, we use "save" method.
However, I would like to understand whether the save method really updates the record or not.
In other words, I would like to know if the content going to save is the same with the existing content in mongoDb. Accordingly, even if save method is executed without any errors, is it possible to understand whether it is really updated or not?
Thanks in advance
There are several ways to checks this.
The first is after calling Save, is to call the getLastError method. Within the console this is just db.getLastError().
This will tell you if an error occurred during the last operation. More details can be found at te following address http://docs.mongodb.org/manual/core/write-operations/#write-concern.
Another way would be to call findAndModify, this will allow you to update the document and either get the updated document back.
http://docs.mongodb.org/manual/reference/command/findAndModify/
Both of these are available in all of the official drivers.
Save method always writes the record.
There is no situation in Mongo where the write would not happen because the record that is being saved is identical to the record that's already there. The write would simply happen and "overwrite" existing data with new data (which happens to be identical).
The only way you can tell is by comparing the old and new documents - and that's a lot of extra work.
I have a requirement to allow a user to specify the value of an InArgument / property from a list of valid values (e.g. a combobox). The list of valid values is determined by the value of another InArgument (the value of which will be set by an expression).
For instance, at design time:
User enters a file path into workflow variable FilePath
The DependedUpon InArgument is set to the value of FilePath
The file is queried and a list of valid values is displayed to the user to select the appropriate value (presumably via a custom PropertyValueEditor).
Is this possible?
Considering this is being done at design time, I'd strongly suggest you provide for all this logic within the designer, rather than in the Activity itself.
Design-time logic shouldn't be contained within your Activity. Your Activity should be able to run independent of any designer. Think about it this way...
You sit down and design your workflow using Activities and their designers. Once done, you install/xcopy the workflows to a server somewhere else. When the server loads that Activity prior to executing it, what happens when your design logic executes in CacheMetadata? Either it is skipped using some heuristic to determine that you are not running in design time, or you include extra logic to skip this code when it is unable to locate that file. Either way, why is a server executing this design time code? The answer is that it shouldn't be executing it; that code belongs with the designers.
This is why, if you look at the framework, you'll see that Activities and their designers exist in different assemblies. Your code should be the same way--design-centric code should be delivered in separate assemblies from your Activities, so that you may deliver both to designers, and only the Activity assemblies to your application servers.
When do you want to validate this, at design time or run time?
Design time is limited because the user can use an expression that depends on another variable and you can't read the value from there at design time. You can however look at the expression and possibly deduce an invalid combination that way. In this case you need to add code to the CacheMetadata function.
At run time you can get the actual values and validate them in the Execute function.
Contrived example:
{
productName: 'Lost Series 67 DVD',
availableFrom: '19/May/2011',
availableTo: '19/Sep/2011'
}
View storeFront/currentlyAvailableProducts basically checks if current datetime is within availableFrom - availableTo and emits the doc.
I would like to force a view to regenerate at 1am every night, i.e. process/map all docs.
At first I had a simple python script scheduled via crontab that touched each document hence causing a new revision and the view to update,however since couchdb is append only this wasnt very efficient - i.e. loads of unnecessary IO and disk space usage followed by compaction, very resource wasteful on all fronts.
Second solution was to push the view definition again via couchapp push however this meant the view was unavailable (or partially unavailable) for several minutes which was also unacceptable.
Is there any other solutions?
Will's answer is great; but just to get the consensus viewpoint represented here:
Keep one view, and query it differently every day
Determine your time-slice size, for example one day.
Next, for each document, you emit once for every time slice (day) that it is available. So if a document is available from 19 May to 21 May (inclusive), your emit keys would be:
"2011-05-19"
"2011-05-20"
"2011-05-21"
Once that is computed for every document, to find docs available on a certain day, just query the view with (e.g. today) ?key="2011-05-18".
You never have to update or re-run your views.
If you must never change your query URL for some reason, you might be able to use a _show function to 302 (temporary) redirect to today's correct query.
So your view is not being updated automatically I take it?
New and changed documents are not being added on the fly?
Oh I see, you're cheating. You're using "out of document" information (i.e. the current date) during view creation.
There's no view renaming, but if you were desperate you could use url rewriting.
Simply create a design document "each day": /db/_design/today05172011
Then use some url rewriting to change: GET /db/_design/today/_view/yourview
to: GET /db/_design/today051711/_view/yourview
Create the view at 11pm server time (tweak it so that "now" is "tomorrow", or whatever).
Then add some more clean up code to later delete the older views.
This way your view builds each night as you like.
Obviously you'll need to front Couch with some other web server/proxy to pull this off.
It's elegant, and inelegant, at the same time.