Hi I use SQLAlchemy for a web application. I want listen an event 'after_insert'.
class MyApp(Base):
...
def listen_after_insert(*args):
...
event.listen(MyApp, 'after_insert', listen_after_insert)
If i add a new app in my session, it 's work
session.add(MyApp(...))
session.commit()
But if the insert come from another application (ex: psql for postgres driver) it isn't work.
Who know how can I get the event if the insert come from another application?
You can't, the events are internal to the application. If you want to detect external changes, you could write a trigger function, perhaps even in PL/Python, to somehow notify your application when certain events happen at the database level.
Related
I was looking at saving some data to my Room database and was reevaluating as there are some places in my repositories where I am extending AsyncTask (I'm still using Java) and wanted to check on the state of things to see if it was a good time to swap them out. I saw this reference in the Android developer site on Approaches to background work.
All persistent work: You should use WorkManager for all forms of
persistent work. Immediate impersistent work: You should use Kotlin
coroutines for immediate impersistent work. For Java programming
language users, see Threading on Android for recommended options.
Long-running and deferrable impersistent work: You should not use
long-running and deferrable impersistent work. You should instead
complete such tasks through persistent work using WorkManager.
I started using WorkManager for an API which needed to be called, but for which I could not rely on network connectivity. Because I'm using Room, which is persistent, it seems like I should be using WorkManager.
It defines persistent work as:
Persistent work: Remains scheduled through app restarts and device reboots.
A database insert/update/delete is persistent by this definition. Scheduled throws me off a little, as I want it to be immediate, but according to this chart that would still apply.
Is anybody using WorkManager as the mechanism for CUD operations in their repositories and if so, do they have an example?
It would be great to see how this all works in an update fragment. If a single item is selected and I am viewing it in a fragment, when changes are made I would need to update the database using a Worker class and view the data using a LiveData object, correct?
Inserts and returning the id (or object) would be interesting to see as well.
My MVC application connects in Oracle database. We created a lot of triggers to save all data changed by users.
inside the trigger, we used the code bellow to get authentcated user:
UPPER(SYS_CONTEXT('USERENV', 'OS_USER'))
When i'm running my application in localhost, the database get the correct user, but when i plublish it on server (IIS), the database always get as user the application pool name.
Is there some IIS configuration that i need to set to get "Windows authentication" user? Is there another way to get this information inside oracle function/trigger?
You would realistically want to use a secure application context which is basically a user-controlled context unlike the system-controlled USERENV context. When the application code gets a connection from the pool, it would call a stored procedure that sets the application username in the new application context. Your triggers would then reference the new context rather than USERENV. Your application needs to ensure that the context is set appropriately every time a connection is acquired from the pool-- if the application fails to set the context correctly, your triggers will get the wrong information.
If you don't want to create your own context, you could use the CLIENT_IDENTIFIER in USERENV which you can set via dbms_session whenever you get a connection from the pool. Functionally, this is basically identical to creating your own context. The nice thing about creating your own context, though, is that you can seamlessly add attributes in the future as you identify the need (i.e. adding the IP address of the client browser or a tier attribute if you have gold, silver, and bronze customers).
There are alternate ways to approach the problem such as using proxy authentication. In general, though, that's not going to work as well with connection pools particularly when you have very large numbers of users.
I am looking for a library that will help me keep some state in sync between my server and my GUI in "real time". I have the messaging and middleware sorted (push updates etc), but what I need is a protocol on top of that which guarantees that the data stays in sync within some reasonably finite period - an error / dropped message / exception might cause the data to go out of syn for a few seconds, but it should resync or at least know it is out of sync within a few seconds.
This seems like it should be something that has been solved before but I can't seem to find anything suitable - any help much appreciated
More detail - I have a Rich Client (Silverlight but likely to move to Javascript/C# or Java soon) GUI that is served by a JMS type middleware.
I am looking to re engineer some of the data interactions to something like as follows
Each user has their own view on several reasonably small data sets for items such as:
Entitlements (what GUI elements to display)
GUI data (e.g. to fill drop down menus etc)
Grids of business data (e.g. a grid of orders)
Preferences (e.g. how the GUI is laid out)
All of these data sets can be changed on the server at any time and the data should update on the client as soon as possible.
Data is changed via the server – the client asks for a change (e.g. cancel a request) and the server validates it against entitlements and business rules and updates its internal data set which would then send the change back to the GUI. In order to provide user feedback an interim state may be set on the gui (cancel submitted or similar) which is the over ridden by the server response.
At the moment the workflow is:
User authenticates
GUI downloads the initial data sets from the server (which either loads them from the database or some other business objects it has cached)
GUI renders
GUI downloads a snapshot of the business data
GUI subscribes to updates to the business data
As updates come in the GUI updates the model and view on screen
I am looking for a generalised library that would improve on this
Should be cross language using an efficient payload format (e.g. Java back end, C# front end, protobuf data format)
Should be transport agnostic (we use a JMS style middleware we don’t want to replace right now)
The client should be sent a update when a change occurs to the server side dataset
The client and server should be able to check for changes to ensure they are up to date
The data sent should be minimal (minimum delta)
Client and Server should cope with being more than one revision out of sync
The client should be able to cache to disk in between session and then just get deltas on login.
I think the ideal solution would be used something like
Any object (or object tree) can be registered with the library code (this should work with data/objects loaded via Hibernate)
When the object changes the library notifys a listener / callback with the change delta
The listener sends that delta to the client using my JMS
The client gets the update and can give that back to the client side version of the library which will update the client side version of the object
The client should get sufficient information from the update to be able to decide what UI action needs to be taken (notify user, update grid etc)
The client and server periodically check that they are on the same version of the object (e.g. server sends the version number to the client) and can remediate if necessary by either the server sending deltas or a complete refresh if necessary.
Thanks for any suggestions
Wow, that's a lot!
I have a project going on which deals with the Synchronization aspect of this in Javascipt on the front end. There is a testing server wrote in Node.JS (it actually was easy once the client was was settled).
Basically data is stored by key in a dataset and every individual key is versioned. The Server has all versions of all data and the Client can be fed changes from the server. Version conflicts for when something is modified on both client and server are handled by a conflict resolution callback.
It is not complete, infact it only has in-memory stores at the moment but that will change over the new week or so.
The actual notification/downloading and uploading is out of scope for the library but you could just use Sockets.IO for this.
It currently works with jQuery, Dojo and NodeJS, really it's got hardly any dependencies at all.
The project (with a demo) is located at https://github.com/forbesmyester/SyncIt
I am in process of developing an MFC based Windows based application, using PostgreSQL which would perform
Fetches information from the UI
Performs some logic and store related information to the database
The stored information has to be send immediately OR at schedule interval (ex. at 5:00 on xyz date) over the network
Currently, we have developed a dispacher mechanism (thread ), which constantly polls the database for new information inserted in the database. The thread fetches the information and send to the network module.
But, I feel this is not the correct approach as
Polling every time is a overhead. There can be times when there is nothing to execute
It is not real time , because we poll after every 5 seconds
So
Is there a way to send a trigger to my network module as soon as information is updated in database?
Or any better way to achieve this task?
Thanks in advance.
You can use the listen/notify feature of PostgreSQL for this.
http://www.postgresql.org/docs/current/static/sql-listen.html
http://www.postgresql.org/docs/current/static/sql-notify.html
The clients interested in the messages would execute a listen statement and the trigger would then notify them.
I don't use C# so, but according to the manual you can retrieve the messages in an asynchronous manner - which still involves some "lightweight" polling as the notification message is only sent as part of the answer of the server. The manual claims that running an "empty" statement (such as ;) will be enough. Using Java/JDBC I used a simple select 42 which doesn't impose a big workload on the server as no tables are touched.
This polling is defintely faster and more scalable than actually retrieving the table's data.
Yes you are right #RDX, you shouldnt poll it every time rather you could write a trigger in Postgres and from that trigger try calling a java program which could be seen in the below thread.
Calling java pgm from Postgres trigger
I have run into a situation where I need to open a newly created quote at the end of a workflow. I have a feeling this is going to require me to create a a very simple custom workflow that uses "window.open", but I would like to avoid this if anyone has a better idea.
So I need to open a newly created quote as soon as it is created in a workflow. Anyone have any good ideas on how to do this?
Workflows are asynchronous; they run on the server (as opposed to the client) and do not run in realtime. eg a workflow that is triggered by creation of a record will run on the server sometime after the record is created (depending on system load etc - it could be a second or two, or could be half an hour later. If you have stopped the CRM Async service on the server, they might well never run.)
Because they run on the server the user has no interaction with them. As a result you can't open a window, as there's no user involved to open a window for...
What you probably want to do is make use of Dialogs (introduced in CRM 2011). You won't be able to use window.open() but as long as you've got a recent update rollup installed on the server you can present the user with a hyperlink to most CRM records.
Setup of Dialogs is much the same as Workflows, and they use the same mechanics under the hood. The difference is that they're syncronous (i.e. run in real-time) and they are client-side. There's some detail on Technet: http://technet.microsoft.com/en-us/library/gg334463.aspx