I have a web app. developed by asp(c#) and sql data base , now I develop mobile app with ionic 3 , what is the best method to connecting to the same sql data base?

I found some methods but I cannot decide yet , such as (firebase , Backand) or web service

Write REST-services to communicatie with your SQL database.
A direct connection between the app and database is strongly discouraged.

Thank you MattE , I know that direct connection between the app and database is strongly discouraged , my question is “I must make aREST-service or I can use any backend like firebase, backand,…”

You can’t use Firebase here, because that requires you to use a firebaseDB.
I don’t have any experience with Backand, so I can’t comment on that.

But as you have your own database, I would suggest to build your own backend (in NodeJs, C#, …) to make the REST-services available and provide a connection to your SQL DB.

can you show me a documentation explaining this ?

Just search “REST nodeJs” or “REST c#” in Google and you should find plenty of documentation

Thank you MattE

just one question, Is the backend I will build contains push notifications or I will use an other service supporting push notifications ?

It’s best to have an external provider handle the push notifications (OneSignal, Pushwoosh, firebase, …).
From your own backend, you can do a post request to the notificationprovider to send your notifications.

So what is the difference between ionic local notification and push notification ?