Android Room: One database with multiple tables

Question

I have two separate tables for my application, one is called users and the other is called passwords.

Users:

@Entity(tableName = "users")
public class Users {
   // some setters and getters here
}

Passwords:

@Entity(tableName = "passwords")
public class Passwords {
   // some setters and getters here
}

And this is how I'm accessing the database:

usersdb = Room.databaseBuilder(this, Users.class,"mymaindb")
          .allowMainThreadQueries()
          .build();

// Then later in some other activity when I need to use passwords table

passwords = Room.databaseBuilder(this, passwords.class,"mymaindb")
          .allowMainThreadQueries()
          .build();

The issue I'm having is that after a fresh install, when I access passwords then I can't access users or vice versa.

I get the following error:

Caused by: java.lang.IllegalStateException: Room cannot verify the data integrity. Looks like you've changed schema but forgot to update the version number. You can simply fix this by increasing the version number.

But when I try to have two separate databases like passwords_db and users_db instead of mymaindb, then it works completely fine.

So is there a way I can have multiple tables under one database? If so, what am I doing wrong then? Thanks in advance!

You got a version of your database with one table. Then you update it and Room asked you to increase the version of your database. Is it so? Room is trying to help you *"Room cannot verify the data integrity. Looks like you've changed schema but forgot to update the version number."*. — Blind Kai, Aug 13 '19 at 07:49

Bach Vu · Accepted Answer · 2019-08-13T08:06:18.917

35

I think you got this all wrong, Room.databaseBuilder should only be called once to setup the database and in that database class, you will construct multiple tables. For example:

Room.databaseBuilder(this, MyRoomDb.class, "mymaindb")
                .allowMainThreadQueries()
                .build()

And your MyRoomDb should look like this

@Database(
        entities = {
            Users.class,
            Passwords.class
        },
        version = VERSION
)
public abstract class MyRoomDb extends RoomDatabase {
...
}

edited Aug 13 '19 at 08:06

answered Aug 13 '19 at 08:01

Bach Vu

2,298
1
15
19

You were right, thanks! Now I have one database class and on data access object and it works completely fine. – M. Ather Khan Aug 16 '19 at 05:24
Nice, glad I could help :) – Bach Vu Aug 16 '19 at 06:35
Does RoomDB supports dropAllTables() and createAllTables()? https://stackoverflow.com/questions/62405921/does-roomdb-supports-dropalltables-and-createalltables – K Pradeep Kumar Reddy Jun 16 '20 at 10:07

score 4 · Answer 2 · answered Aug 13 '19 at 07:55

4

You have few variants how to solve this problem:

Add tables back but increase the version of database;

@Database(entities={Users.class, Passwords.class}, version = 2)
Clean the application settings and build the new database;

Just clean the application cache and try to recreate the database.

answered Aug 13 '19 at 07:55

Blind Kai

514
5
14

In case someone needs to know, clearing up the cache and data is needed and an uninstall wouldn't work. This is because the default behavior after Android 6 is to save the data – Sanved Jun 22 '22 at 03:12

HandyPawan · Answer 3 · 2021-01-31T17:29:14.053

3

It's simple like adding one entity table. Just add another table name using ",". And another table will be added.

@Database(entities = [TableUser::class, TableRecord::class], version = 1)

abstract class MyDatabase : RoomDatabase() {
    abstract fun myDao(): MyDao
}

edited Jan 31 '21 at 17:29

answered Jan 31 '21 at 09:51

HandyPawan

1,018
1
11
16

Perhaps you should explain your answer a bit. – René Höhle Jan 31 '21 at 10:30
Don't you need multiple Dao's for every table? – dessalines Dec 19 '22 at 17:09

Félix Maroy · Answer 4 · 2020-12-01T08:09:49.350

Here's another way you can have what you need by using one RoomDB class for all your tables:

@Database(entities = {Users.class, Passwords.class}, version = 1, exportSchema = false)
public abstract class MyDatabase extends RoomDatabase {
private static MyDatabase INSTANCE;

    public abstract UsersDAO usersDAO();
    public abstract PasswordsDAO passwordsDAO();

    public static MyDatabase getDatabase(Context context) {
        if (INSTANCE == null) {
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                    MyDatabase.class, "mydatabase")
                    .build();
        }
        return INSTANCE;
    }
}

Your Entity will look like this:

@Entity(tableName = "user_table")
public class User {

    @PrimaryKey(autoGenerate = true)
    private long id;
    private String username;
    private String email;

    .............//Constructor goes here

    .............//Getters and Setters go here

}

The DAO looks like this:

@Dao
public interface UsersDAO {

    @Query("SELECT * FROM user_table")
    List<User> getAll();

}

Then you'll fetch data like this:

AsyncTask.execute(() -> {               
    MyDatabase.getDatabase(getApplicationContext()).usersDAO().getAll();
});

score 0 · Answer 5 · answered Sep 01 '20 at 20:11

0

if you dont want to change the code you can simply uninstall and install the app again. But this will delete your data saved in database till now.

answered Sep 01 '20 at 20:11

Mohit Mahajan

47
1
7

Android Room: One database with multiple tables

5 Answers5

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