(I'm new to android development)

Say android app-1 created a database hello, via roo.
Then could android app-2 created a database hello, on the same phone?

My guess is yes, since room use sqlite, each app may start a new sqlite instance, and may store its data in private space, otherwise it's too easy to get conflict. But I'm not sure.

The questions are:

• Will 2 app share the same sqlite instance, or each app will start a new sqlite?
• Is the database's name app scoped?
• I guess the data of a database is also private to the application?

(I've searched about this, didn't get a confirm.)

CodePudding user response：

By default, Room databases are stored in internal storage, and each app has its own internal storage. You can have two databases named hello, one per app, without a problem.

CodePudding user response：

Really SQLite is a set is a set of file handling routines (more complex than just simple writes and reads though).

Android devices come with the routines built in (albeit different versions of SQLite which are typically backwards compatible).

Room is a wrapper around SQLite and thus the routines and caters for an object orientated approach to accessing the data (file(s)).

Unlike, for example, MySQL, SQLite it is not a server that manages transactions from extrenal sources, so SQLite is not a running instance background app/service. (The command line interface would be though)

A device can have many Apps that use the routines to access and update the underlying file (3 files if using the default WAL (Write-Ahead Logging, the core database file, the wal file and a third file the shm file a WAL file for the WAL), (2 files if using JOURNAL mode).

• with WAL changes are applied to the WAL file which are then committed at times to the core/master file. Likewise for the shm file in regard to the WAL file. This allows a rollback to simply effectively delete/empty the WAL file.
• JOURNAL mode the journal is a record/log of the changes made to the core database. A rollback is accomplished by reversing the changes according to the JOURNAL.
• WAL is typically more efficient.
• Typically this is all handled by the SQLite routines.

An App can itself access multiple databases if need be. SQLite even caters for accessing multiple database by ATTACHing databases to another.

By default the database is stored in the App's protected data storage area and thus is unique to the App. What you couldn't do, by default, is have the same database name twice within an App

• you could say have two hello databases in different locations e.g. data/data/the_package/databases/hello and data/data/myotherdatabasesfolder/hello
  • note sure how you would go about this using Room though, certainly feasible using just the SQLite API.

So App1 and App2 could have the same hello database as the files will be in separate App specific locations (data/data/the_apps_package_name/databases by default).