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Did you tried changing directory inside python instead of cmd ?

it refuses to add it because it already exists,

Use CREATE INDEX IF NOT EXISTS myIndex ON myTable (col1,col2)

You should use it in the onOpen function.

Alternately if using Room 2.4.0-beta2 or greater then there is a prePackagedDatabase callback which you could use to do the same BUT only when the Pre-Packaged database is copied.

1. The onOpen function will be invoked every time the database is built/opened (not an issue as the index existing will result in minimal overheads).

2. Whilst the prePackagedDatabase callback is only invoked when the database is created/copied from the asset.

3. The onCreate function only runs when Room creates the database. It does not create the database when createFromAsset (or File) is used. However, if you use fallbackToDestructiveMigration AND there is no Migration covering the from/to versions then onCreate is called.

The correct solution would be to include the index in the Pre-Packaged database, it would then always exist.

I can't seem to understand why Room complains about the indice, it refuses to add it because it already exists, running an empty migration fixes the problem, not running any migration gives me a verification exception.

If you run a fresh installation, then as the index is defined in the Entity it will create the index. Hence why it already exists (IF NOT EXISTS doesn't create it if it already exists).

Not running a migration fails because room generates an identity_hash based upon the Entities. Change the entity and room sees that the identity hash has changed.

You may find looking at the generated java (visible from the Android View in Android Studio) looking for the class that is the class annotated with @Database but with the _Impl suffix and looking in that class for the createAllTables method. This includes all the tables and indexes that Room will create.

You would see the room_master table that holds the identity_hash that is compared against the one in the package. You would also see that Room includes IF NOT EXISTS on all CREATE statements.

It can be done using apply() and lambda functions

The stack trace in the error appears like you are calling app.listen() somewhere (probably from your server.js - line 13). You need to go find that code and remove it. You only want to attempt to start your same server once and your http.listen() is already starting it once.

Just to demonstrate the difference between your two cases, take this example. When I call a function immediately in the returned JSX code, it fires as soon as the element mounts. However, in the second button, I have to click it before the logging will happen.

and int i is different for every JButton, because it needs to be the int i from that for-loop.

One way is to set the "action command" for the button.

When you create the button you use: