I'm currently working on a requirement that is to "replace the previously developed Polling mechanism for change notifications of database".
Let me elaborate a little:
We have an oracle database where we have put some triggers to get notified for any changes on the table. Using it, we were trying to get changed data and converting it into an XML/Json which is the request-body of an WEBAPI to perform a POST operation in another database.
The new requirement is to skip the polling mechanism and come up with something like "rather than we call the database for notifications, it calls us every time it gets updated".
I did a little googling and everyone suggest for the best approach as:
Database Change Notifications. Here I need to grant permissions to Oracle and then create an application in .Net where I can write a callback function for future processing. Until here, I'm good but my question is:
The .Net application I need to create that communicates with the database is required to be a Web application and has to be online always? Can I create a console application to get notified, if yes, how will the database contact my application for any change? What exactly is the internal process going on when the database notifies my application for any change?
Related
I want to building a Blazor WebAssembly Progressive Web App, that can run offline.
I began Blazor this morning, and I'm just trying to get the hang of it.
To begin I want to do something like keep.google.com. You can work on you notes offline, on different devices, and when the connection is re-established, all notes are synchronized in the background with the server.
My idea is to have simple notes on a server, with an id, title and a message. These notes can be displayed and added/modified from the client. Since I want the application to work offline, I want the synchronization process to be as follows:
The fist time visiting the website, all notes are fetched from the server,
When notes are added/modified, they are saved on the server,
If connection is lost, notes can still be read and added/modified localy,
When the connection is re-established, the modifications are saved to the server,
Periodically or after pressing a button, sync is done between client and server to fetch new data present on the server.
I think the way to do this is to have a copy of the database localy. Client do modification on the local database and periodically/after pressing a button/when connection is re-established, I sync local database with server database.
I'm sure there is an official and easy solution to do that. I followed the CarChecker example from Microsoft, but they used the IndexedDB in javascript to do that (23min13 in the official tutorial video).
Do you know a .NET solution/tutorial/service that store data locally, and sync in the background with the server ?
I wrote a Blazor WebAssembly PWA with similar technical requirements. There is certainly more than one way to accomplish this but the steps I used are as follows:
I used sqlite on the client side to persitist the data locally. The simplest way to make that persist-able with the ability to use Entity Framework is to use the SqliteWasmHelper nuget package. https://github.com/JeremyLikness/SqliteWasmHelper
On startup and/or when online I fetch the necessary data and insert it into the local sqlite database.
The user can make changes and I save that to the local sqlite DB and mark it as ready to be synced.
I have a background service with a timer which executes on a configurable interval and grabs the local data marked to be synced and calls the API on the server to save the data to a SQL Server database. Of course I check to see that the user is online before attempting the sync.
I use Javascript to determine whether the device is online. I can provide that to you if you need but you should be able to google it.
I have an application update checker based on this method which works pretty well: https://whuysentruit.medium.com/blazor-wasm-pwa-adding-a-new-update-available-notification-d9f65c4ad13
I hope that helps. I'm happy to provide more detail if you like.
I have an application with one DB which is used by many users. Whenever one user makes changes, we save the changes to the database.
Now, I need to notify other logged-in users about this change. How can this be done?
I'm thinking - when the application succcessfully saves / updates the data in the database, the application will send a notification to the connected clients with the new record updated or added.
I'm using C# and SQL Server database.
Your immediate options are push-based notifications with something like a message bus, or polling loops on known ids.
Message busses operate on publish-subscribe models which work well for Windows applications. Have a look at MassTransit or MSMQ as a starting point. There are plenty of options out there. They can be combined into web apps using something that essentially wraps a polling loop with the client like SignalR.
Polling-based options work typically on a timer and do quick timestamp or version # checks against the database, reloading a record if a difference is found.
Push-based are more efficient but only notify of changes between supported applications. (Client to Client) they don't detect changes by applications that don't participate as publishers, nor do they see changes made directly to the database.
Polling-based options cover all changes, but are generally slower and require a schema that has version information to work effectively.
The scenario is that our client owns and manages a system (we wrote it) hosted at their clients premises. Their client is contractually restricted from changing any data in the database behind the system but they could change the data if they chose because they have full admin rights (the server is procured by them and hosted on their premises).
The requirement is to get notification if they change any data. For now, please ignore deleting data, this discussion is about amendments to data in tables.
We are using Linq to Sql and have overridden the data context so that for each read of the data, we compare a hash of the rows data against a stored hash, previously made during insert/update, held on each row in the table.
We are concerned about scalability so I would like to know if anyone has any other ideas. We are trying to get notified of data changes in SSMS, queries run directly on the db, etc. Also, if someone was to stop our service (Windows service), upon startup we would need to know a row had been changed. Any thoughts?
EDIT: Let me just clarify as I could have been clearer. We are not necessarily trying to stop changes being made (this is impossible as they have full access) more get notified if they change the data.
The answer is simple: to prevent the client directly manipulating the data, store it out of their reach in a Windows Azure or Amazon EC2 instance. The most they will be able to do is get the connection string which will then connect them as a limited rights user.
Also, if someone was to stop our service (Windows service), upon startup we would need to know a row had been changed.
You can create triggers which will write whatever info you want to an audit table, you can then inspect the audit table to determine changes made by your application and directly by the client. Auditing database changes is a well known problem that has been solved many times before, there is plenty of information out there about it.
for each read of the data, we compare a hash of the rows data against a stored hash
As you can probably guess, this is painfully slow and not scalable.
I need to create a desktop WPF application in .NET.
The application communicates with a web server, and can work in offline mode when the web server isn't available.
For example the application needs to calculate how much time the user works on a project. The application connects to the server and gets a list of projects, the user selects one project, and presses a button to start timer. The user can later stop the timer. The project start and stop times need to be sent to the server.
How to implement this functionality when the application is in offline mode?
Is there are some existing solution or some libraries to simplify this task?
Thanks in advance.
You'll need to do a couple of things differently in order to work offline.
First, you'll need to cache a list of projects. This way, the user doesn't have to go online to get the project list - you can pull it from your local cache when the user is offline.
Secondly, you'll need to save your timing results locally. Once you go online again, you can update the server will all of the historic timing data.
This just requires saving the information locally. You can choose to save it anywhere you wish, and even a simple XML file would suffice for the information you're saving, since it's simple - just a project + a timespan.
It sounds like this is a timing application for business tracking purposes, in which case you'll want to prevent the user from easily changing the data. Personally, I would probably save this in Isolated Storage, and potentially encrypt it.
You can use Sql Server Compact for you local storage and then you microsoft sync framework to sync your local database to the server database. I recommend doing some research on the Microsoft Sync Framework.
Hello all I implemented this application I've created my own off-line framework
based on this article and Microsoft Disconnected Service Agent
DSA
I've adapted this framework for my needs.
Thank you for all.
you can use a typed or untyped dataset for offline-storage.
when online (connected to internet) you can download the data into a dataset and upload it back to the database server. the dataset can be loaded from and saved to a local file.
I have a datalogging application (c#/.net) that logs data to a SQLite database. This database is written to constantly while the application is running. It is also possible for the database to be archived and a new database created once the size of the SQLite database reaches a predefined size.
I'm writing a web application for reporting on the data. My web setup is c#/.Net with a SQL Server. Clients will be able to see their own data gathered online from their instance of my application.
For test purposes, to upload the data to test with I've written a rough and dirty application which basically reads from the SQLite DB and then injects the data into the SQL Server using SQL - I run the application once to populate the SQL Server DB online.
My application is written in c# and is modular so I could add a process that periodically checks the SQLite DB then transfer new data in batches to my SQL Server.
My question is, if I wanted to continually synchronise the client side SQLLite database (s) with my server as the application is datalogging what would the best way of going about this be?
Is there any technology/strategy I should be looking into employing here? Any recommended techniques?
Several options come to mind. You can add a timestamp to each table that you want to copy from and then select rows written after the last update. This is fast and will work if you archive the database and start with an empty one.
You can also journal your updates for each table into an XML string that describes the changes and store that into a new table that is treated as a queue.
You could take a look at the Sync Framework. How complex is the schema that you're looking to sync up & is it only one-way or does data need to come back down?
As a simply solution I'd look at exporting data in some delimited format and then using bcp/BULK INSERT to pull it in to your central server.
Might want to investigate concept of Log Shipping
There exists a open source project on Github also available on Nuget. It is called SyncWinR, it implements the Sync Framework Toolkit to enabled synchronization with WinRT or Windows Phone 8 and SQLite.
You can access the project from https://github.com/Mimetis/SyncWinRT.