I'm having a strange problem with ASP.NET MVC4 and Entity Framework 5: The web application I'm building retrieves data from a database and sends it as Json into a viewmodel on the page, from which it then gets presented in a table on the page. The data represents the state of some datapoints that change every now and then.
Now I observed the following behaviour:
when I run the web application from my development server, everything works fine and the shown data is up to date.
when I deploy the web app to a production server (which talks to the very same DB), the page does not represent the current state of the data
I can't breakpoint the controller method that retrieves the data, as it only occurs on the production server, but when I look into the Json data I can see that it actually is old data. So it seems like EF is caching the retrieved data. This is a serious problem as we use this web application for industrial monitoring purposes and therefore need to rely on up-to-date data.
Has anyone encountered the same issue? Any help on this is greatly appreciated!
I don't know entity framework that well but I think this has something to do with change tracking. I'd try disabling it to force EF to re-query the DB, I think (and others please can correct me if I'm wrong) but unless SaveChanges has been called on an ObjectContext if you re-query the same data the database won't be queried again.
I've used MergeOption = MergeOption.NoTracking (on the ObjectSet) to turn it off in my project.
Related
Can someone explain to me why you can't connect to a MySQL DB directly through dart from a security point of view?
There is no hard guideline on whether to connect frontend directly to backend or not. It is just a design practice that has been widely accepted and evolved over many years.
Typical app structure consists of
FRONTEND -> SOME MIDDLE LAYER -> BACKEND
Where your middle layer handles all the interactions/processing with the database and the frontend uses this functionality with some sort of API structure. Having this layer is extremely helpful when the application goes to scale, it gives an added abstraction to the frontend.
It is not advisable to directly fuse your frontend(your flutter app), to the DB(MySQL) because any efficient hacker might use basic man-in-middle attack to know your DB structure/connections/queries(There are some pretty effective decompilers present out there), and alter your data and you might not even get to know what caused the data to update unless you've applied some checks on DB layer.
Also, your frontend logic needs to be more of end-user centric than to handle the data of the user. Any backend system(java, node, etc) gives you added functionality & freedom to parse and present the data from either side.
You can use the sqlite package available to store basic data, like your session tokens, your app configurations etc, but it is advisable to keep the main user data like the logins, etc in a separate place, or better yet, you can use the firebase plugin to store data in document structure in the cloud.
I'm working on a project that can take data from a Weintek HMI, put them on a webserver and then send them to an application that I created on android studio.
I've found firebase that can help me in this task.
In easybuilder that works with my hmi, I can create a mysql database that can store the data.
The problem is how can I update automatically firebase database with mysql database with an interval of time in order to access them on the android app.
If there is no solution with mysql, can someone suggest other method to extract the data and use some web server to sync it with the android app?
I don't know your specific need, in terms of data volume or application, but as a workaround, maybe this can help you:
I usually apply MQTT, which many Weintek HMIs have, to send telemetry data, and then use NodeRed to process and redirect the data to a database, email, SMS, Telegram, CSV, TXT... depending on the need , which in your case could be Firebase (I never used it).
It works great for me as I don't have to worry about HMI limitations.
The problem is the reliability of the data, in terms of confirming that when the HMI sends, the server listens and writes, but there are certainly ways to deal with this, and the fact that you need to have a server with NodeRed running.
If you have never done so, in Weintek HMIs you can send the MQTT payload cyclically using macros easily.
I'm struggling to find a solution to what I thought would be a common requirement so I'm hoping someone can help me with some pointers on what to search for/areas to explore.
Background
I'm building an iOS mobile app. I'm storing data locally using realm.io. The app is preinstalled with a snapshot of the content of a Wordpress mySQL database (it uses custom types). The content of the WP database is only written via the Wordpress install, the mobile app cannot write data.
Objective
So, I want to be able to check for changes since a given date (whenever the local database was last updated) and send the changed records to the mobile app (via the wp JSON api?).
I think I can fetch "posts since a date" but I need a full list of all create, update and delete operations since a given date.
Since the app is read-only I thought this type of one-way sync would be pretty straight forward but I can't find a common solution.
Any ideas to point me in the right direction would be great. Obviously, if anyone has any experience of doing this sort if thing with realm.io then that would be amazing :-)
Realm doesn't support yet any sort of synchronization mechanism across different files. We have an issue about that though, but you're likely searching rather for a solution in the immediate future.
Update: Realm launched the Realm Mobile Platform. This offers synchronization functionalities and would greatly simplify the solution for this use case.
You could use e.g. the server-side Node.js binding to pull new data from your MySQL Wordpress installation and push them to a global Realm served by the Realm Object Server. This can be read-only synchronized from the mobile apps, which would automatically receive the deltas and provide updated data to your users.
Whatever mechanism you come up yourself though in the meantime, it would require that you have read-write access from your iOS application to the realm database, so that you can update it with new data.
Pushing changed records as you describe is likely not going to work.
Apple's Push Notification service (APNS), which is the only back communication channel that works when your app is in the background or suspended, allows you to send very small payloads. You would use that to signalize your iOS app, that something changed on the server-side and there is new data to load. You would then initiate a request to a JSON-based API, wait for the response, map the returned JSON to Realm objects and store them in your database.
You want probably read more in the "Downloading Content in the Background" section of background execution chapter in the official App Programming Guides for iOS.
While pre-seeding the database from the app bundle seems like a nice idea, because the user wouldn't need to wait initially after downloading the app, that will enlarge the app itself with data, which might become in the future completely irrelevant.
Basically I need to connect a MySql database to an IOS application and save a local copy to the device but i'm confused about which path I should take to do this.
Here is a basic description of the application:
The application is used to replace multiple paper based forms, allowing the user to complete a desired form on an iPad. Once the user has completed the form, the forms data is uploaded to a server.
Some forms have fields where the user is required to 'select' an option (drop down list). These options need to be pulled from a database because the options will be changed regularly.
The application still needs to work if there is no internet connection!
This means that whenever there is a connection the application needs to save a copy of the current database so that any required information to fill out forms is still available even if there is no connection.
In short my question is: What is my best option to save a local copy of a database (or just a few tables) to an IOS application?
You should look into Core Data. If you're trying to keep an updated copy of a couple tables, I would create a Core Data database that contains the information you need for your app and, every time the user uses your app, check to see if there's an internet connection. If there is, use NSURLSession to download the necessary data from the web server, after which you can compare the downloaded data to that which is in your Core Data database. If there are any discrepancies between the two, you can update your Core Data database as needed. This way you will always have a relatively up-to-date copy of your MySQL database.
This is a good tutorial for getting a feel for NSURLSession in case you haven't used it much.
Hope it helps!
I am running into a problem using couchbase, but it may be because I don't quite understand how couchbase works. I have created a simple console .NET app to do some simple stores and gets on data. The problem I am having is when I close the app, then restart it and try to get data I previously stored, it will not retrieve any data. But, if I store and then get before closing the app, it returns data. Can anyone offer me clarification? Thanks!
Found my problem... I was not disposing of the client properly. I had the client as a member of another class, which is what I had in my using statement, so I guess that does not properly dispose.