In my android studio in data/data/com.../databases there are 3 files .db, shm.db , wal.db and when i save that .db file it is not showing any table.
While in my another mobile phone files there are only two .db, journal.db and it is showing the table and data when we save it .
i don't know why it is happening ???
If you want to check the database contents, you need to downlaod all those 3 files, store them together in a folder and then you would be able to check the contents of your db.
Your problem:
You are only trying to download the .db extension file. Thats why the issue is coming!
On later versions of Android SQLite Write Ahead logging is enabled by default.
Write ahead logging creates the Wal file, see https://sqlite.org/wal.html for more details.
When the database is closed then the contents of the Wal file will be committed to the main DB file, there is also automatic checkpointing and you can trigger it manually.
It is possible to disable it on a per connection basis, but if data does not get moved to the main db file when you application has been closed then your code is not closing the database properly.
Related
Last time I notice that my app has a problem with SQLite database backup. To do db backup I was copying *.db file from /data/data/com.pkg.app/databases/db_name.db to internal storage. To restore I copying from internal storage to /data/data/com.pkg.app/databases/db_name.db. But in Android P There is something wrong. Those db file exists but its weight is 4kB. When I opened those file by DB Browser I noticed that file is empty - there is no tables and data. It is strange because app is working correctly. The question is where should I look for db file that my app is using? Android 8 and less has no this problem. I am using emulator.
In Android P+ WAL (Write ahead logging) is turned on by default. This results in two additional files that suffix the original file name with -shm (shared memory file) and -wal (the write ahead logging).
These either need to be copied when backing up and restored or you need to backup only after ensuring that the database has been fully checkpointed, you can then delete the -shm and -wal files as part of the restore process.
An alternative is to disable WAL and use the less efficient journal mode.
You may wish to check out Database Import and Export not working in Android Pie.
So I want to view my db structure through some db browser application, but for that I need to get mydatabase.db file from application installed on emulator. I found this file through Device File explorer under data/data/package.com/mydatabase.db but when I open this file in some sqlite editor it shows that its empty no tables etc.. I'm using Room database so I'm thinking maybe room does something to this file that I can't open it because under database folder there is three files mydatabase.db, mydatabase.db-shm, mydatabase.db-wal which I never seen before when I was using just sqlite and maybe there is other ways to check structure of my db?
The -wal file is for write-ahead logging (WAL), which Room 1.1.0 enables. Try copying all three files, then opening the .db file.
WAL is a standard SQLite feature and has been around for years, so most up-to-date SQLite clients should be able to handle it.
I know about copying the database file solutoin,
How do I backup a database file to the SD card on Android?
Android backup/restore: how to backup an internal database?
Android backup/restore: how to backup an internal database?
in fact I was backing up my databases using this method, and up until a little while ago it was working perfectly.
until some multi-thread stuff made me use of enableWriteAheadLogging
now I have two more files near the database file with .db-wal and .db-shm extensions.
copying just the datbase file .db is not working as most of the times the file does not contain the latest database commits (which are available throw app itself) however when I copy three files together it seems to work fine (not quit sure, albeit)
as Sqlite people recommend, the best practice for backing up a sqlite database is to use backup api but can someone guid me on how I can use this api from inside an application, or even use sqlite .dump (How do I dump the data of some SQLite3 tables?) method from inside an app ?
So Which one is the best practice to back up a sqlite database from an android app?
1- Copy all the database-related files from the sandbox
2- Use sqlite Backup Api
3- Use sqlite .dump
4- any other method
The SQLite backup API is the only mechanism that works correctly with concurrent write accesses from other threads/processes. Which of course means that the Android database framework does not give you access to it.
If you are sure that there are not any active connections, you can just copy all files. (Leaving out journal or WAL files would lead to data corruption.) In the case of WAL, the -shm file
does not contain any permanent data and could be omitted.
The VACUUM INTO command introduced in SQLite version 3.27.0 (2019-02-07) can serve as an alternative to the backup API.
I am developing an android application with inbuilt SQLite database. I need to replace SQLite database file only every 3 months. while doing this I should not alter any part of code.
Also I don't want to do this as upgrading application where changing app version I can replace old application with newer version and new database.
For example if I give a button "Update Database" and after clicking this button only database file is replaced using internet and other parts of application remains intact.
simply do as you'd do with any file:
Download the database file from a web server to the devices temp directory (or cache or SDCard)
Move that file to your application's data directory
To do that automatically, you should use a service started by the AlarmManager.
The database file is identified by Dalvik when I insert it via the Dalvik Debug Monitor Server (DDMS), but when I add the database to the project assest it doesn't even upload to the device (as I can see through the DDMS). How to fix it?
Adding a sqlite db to the assets folder will not make it available for you to use it.
Your db should be copied to /data/data/YOUR_PACKAGE/databases/ on the first run.
Check this link.