CODEWITHSUNDEEP
androidandroid-sqliteandroid-roomandroid-databasesql-update
Harsh Shah
Harsh Shah

Reputation: 2332

Room DB Upgrade need to write full insert query

Hi I am developing an android app and I am using room DB and I have created one table and now I want to add another table I need to write a migration for that and in-migration I need to write full SQL queries for the new table assume I have more than 20 fields how complex will be the query.

In SQLite, we need to write such complex queries which sometimes becomes complicated to write and find errors So, room DB came to resue but now we need to do the same in the room DB migration. How does it useful then?

If we use SQLite, then if we already added one table and now We want to add another table then we can just uninstall the application and new tables will be generated, but in-room DB this is not a case I tried the same thing but it is still showing me that you need to write a migration for the new table. So, in this case, while developing there will a lot of migration scripts that will be hard to maintain at some point in the future.

How does it useful then I have to write a multiple create queries while developing the app this is a very basic flow in any application.

Once we go to prodution then it makes sense to write migration for every table but not in the developing mode.

How does room DB make developr job eaiser?

Upvotes: 2

Views: 1000

Answers (3)

Abhijeet Kumar
Abhijeet Kumar

Reputation: 341

Harsh your question is valid in some way but as you know android is maintaining SQLite database and libraries like room, greendao or even native SQLiteOpenHelper is handling the transaction with sqllite behind the scene for the developers.

In all the earlier libraries too you have to maintain versions of your database and which fields or tables have been added to your database and write migrations for the version upgrades of the database.

The beauty of room comes in play in how easy they have made the CRUD operations on the SQLite database and getting data wrapped in LiveData or Observable, not that you don't need to write migrations.

Upvotes: 1

MikeT
MikeT

Reputation: 56953

I have more than 20 fields how complex will be the query.

It can be very simple as an Entity defines an Object e.g. your 20 columns and to get the 20 columns can be as simple as

@Query(SELECT * FROM thetable)
List<Thetable> getAll();

The above being in an Interface that is annotated with @Dao and all you do in the code is retrieve an instance from the built room database and then use the getAll method which returns a List of Thetable objects. Each with all the member variables populated from the database.

e.g. you could have :-

  mMyTheTableDaoObject = mMyBuiltRoomDatabase.getAll();
  List<TheTable> myTheTableList = mMyTheTableDaoObject.getAll();
  for(TheTable t: myTheTableList) {
     int current???? = t.get????();
  }

While using standard/non-room then you would have to do something along the lines of :-

SQLitedatabase db = whatever_you_need_to_do_to_get_an_SQLiteDatabase_instance;
Cursor c = db.query("theTable",null,null,null,null,null,null);
ArrayList<TheTable> myTheTableList  = new ArrayList();
while(c.moveToNext()) {
    currentTheTable = new TheTable();
    current.TheTable.setId = c.getLong(c.getColumnIndex("id");
    current.TheTable.setNextColumn1 = c.getString("next_column1");
    current.TheTable.setNextColumn2 = c.getString("next_column2");
    ........ another 17 similar lines of code
    currentTheTable.setNextColumn20 = c.getString("next_column20"); 
    myTheTableList.add(currentTheTable);
}
for(TheTable t: myTheTableList) {
   int current???? = t.get????();
}

If we use SQLite, then if we already added one table and now We want to add another table then we can just uninstall the application and new tables will be generated, but in-room DB this is not a case I tried the same thing but it is still showing me that you need to write a migration for the new table.

Once we go to production then it makes sense to write migration for every table but not in the developing mode.

Rather then migrating simply delete the database (delete the App's data or uninstall the App, the database is stored in the default location (data/data/package_name/databases)) and rerun without changing the version. The database will be created as per the new schema. Perhaps utilising temporary code to load data accordingly.

How does room DB make developr job eaiser?

In Short ROOM generates what is termed as the boilerplate code from relatively simple code e.g the @Query above writes the underlying code to extract the data and build the objects (e.g. the code as above).

Upvotes: 2

Md. Asaduzzaman
Md. Asaduzzaman

Reputation: 15423

Please check the official document: https://developer.android.com/training/data-storage/room/migrating-db-versions

Actually Room using SQLITE behind the scene. It provide you plethora of other facilities. In case of Migration you have to write full code to create table.

Upvotes: 1

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