RoomDatabase | Quick Sample to demonstrate how to implement Room Database | Database library

I was able to figure out the issue.

The root cause was the default AmountJsonAdapter created by Moshi was not internally using the CurrencyJsonAdapter.

1. Create custom JSON adapter for Amount rather than Currency.
2. Add AmountJsonAdapter() instead of CurrencyJsonAdapter() in Moshi.Builder().
3. Disable moshi adapter generation for Amount.

Moshi Builder

Using the singleton approach will only even build one of the databases. Once an instance has been retrieved then INSTANCE will no longer be null, so will return the already built database.

Here's an example of multiple databases but intended for an unknown number (and hence a master database used to store the known/created databases). It does allow switching between databases. So you might be able to adapt/simplify this to suite your needs.

Can Android Room manage multiple databases and create databases from a template database?

The databaseBuilder doesn't actually initialise the database, rather it returns an AppDatabase object (in your case). When that returned AppDatabase object is used to access the database (typically via one of the @Dao annotated functions) then it will either open the database if it exists or initialise(create) it.

Having the .createFromAsset means that the create will copy the file from the asset rather than create the database according to the classes specified as entities in the @Database annotation.

In short once the database exists, it exists, it will not be initialised/created, every time the App is run.

Often a singleton approach is used, thus you have a single AppDatabase object that you retrieve throughout the App.

My question is, where does this code go?

If using a singleton approach then probably in the AppDatabase class.

e.g.

It appears that you are not invoking the build function and probably have another means of building the database (invoking the databaseBuilder).

e.g. In an activity/fragment you have something like :-

You have a number of issues.

Issue 1 - private var .... versus just var ....

Typically, within a Data Class just var .... is used. However, if made private then for room you need to have getters and setters so as to be able to access the member variables.

So you could use :-

You should be using:-

Is CoroutineScope(SupervisorJob()) runs in Main scope?

No. By default CoroutineScope() uses Dispatchers.Default, as can be found in the documentation:

CoroutineScope() uses Dispatchers.Default for its coroutines.

isn't all the Room operations supposed to run in non-UI scope?

I'm not very familiar specifically with Room, but generally speaking it depends if the operation is suspending or blocking. You can run suspend functions from any dispatcher/thread. deleteAll() and insert() functions in the example are marked as suspend, therefore you can run them from both UI and non-UI threads.

Digging through the room documentation doesn't turn much up, my hunch is that it has to do with the fact that you are using Automigrations instead of implemented migrations. Have you tried changing that Automigration from 1->2 to an implemented migration?

Also, since you are manually replacing it with a new database that has prepopulated data my solution would be to just get rid of the old migrations, change the name of the DB slightly and start over from version 1. There's no reason to maintain the old migrations if anyone going from older versions to the current version are having their DB deleted.

i solved my problem but i don't know what i changed on background i just seperate my one function to two function in MovieListesiViewmodel and gave a parameter and its worked like a miracle