I'm working on setting up a small SQLite database in my app, which so far has been storing data in the OS MediaStore. I want to migrate away from that, and use Room.
The initial table is very simple, basically just a TEXT field for a description, and some IDs to the actual image in the MediaStore. However, I want to set up a couple of other tables, too. Does this look somewhat sensible:
import android.provider.BaseColumns;
import android.provider.MediaStore;
public class AlbumContract {
public static class PhotoEntry implements BaseColumns {
public static final String TABLE_NAME = "photo";
public static final String COLUMN_NAME_IMAGE_ID = "fk_image_id";
public static final String COLUMN_NAME_IMAGE_URI = "mediastore_uri";
public static final String COLUMN_NAME_EVENT_ID = "fk_event_id";
public static final String COLUMN_NAME_STACK_ID = "fk_stack_id";
public static final String COLUMN_NAME_DESCRIPTION = "description";
}
public static class StackEntry implements BaseColumns {
public static final String TABLE_NAME = "stack";
public static final String COLUMN_NAME_STACK_LEADER = "fk_photo_id";
}
public static class EventEntry implements BaseColumns {
public static final String TABLE_NAME = "event";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_SUBTITLE = "subtitle";
public static final String COLUMN_NAME_ALBUM_ID = "fk_album_id";
}
public static class AlbumEntry implements BaseColumns {
public static final String TABLE_NAME = "album";
public static final String COLUMN_NAME_TITLE = "title";
public static final String COLUMN_NAME_SUBTITLE = "subtitle";
}
public static final String SQL_CREATE_PHOTO =
"CREATE TABLE " + PhotoEntry.TABLE_NAME + " (" +
PhotoEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
PhotoEntry.COLUMN_NAME_IMAGE_ID + " INTEGER, " +
PhotoEntry.COLUMN_NAME_IMAGE_URI + " TEXT, " +
PhotoEntry.COLUMN_NAME_STACK_ID + " INTEGER, " +
PhotoEntry.COLUMN_NAME_EVENT_ID + " INTEGER, " +
PhotoEntry.COLUMN_NAME_DESCRIPTION + " TEXT, " +
// Foreign key to MediaStore.Images
"FOREIGN KEY (" + PhotoEntry.COLUMN_NAME_IMAGE_ID + ") " +
"REFERENCES " + MediaStore.Images.Media.EXTERNAL_CONTENT_URI + "(" + MediaStore.Images.Media._ID + ") " +
// Foreign key to "stack" table
"FOREIGN KEY (" + PhotoEntry.COLUMN_NAME_STACK_ID + ") " +
"REFERENCES " + StackEntry.TABLE_NAME + "(" + StackEntry._ID + ") " +
// Foreign key to "event" table
"FOREIGN KEY (" + PhotoEntry.COLUMN_NAME_EVENT_ID + ") " +
"REFERENCES " + EventEntry.TABLE_NAME + "(" + EventEntry._ID + ") " +
")";
public static final String SQL_CREATE_STACK =
"CREATE TABLE " + StackEntry.TABLE_NAME + " (" +
StackEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
StackEntry.COLUMN_NAME_STACK_LEADER + " INTEGER " +
"FOREIGN KEY (" + StackEntry.COLUMN_NAME_STACK_LEADER + ") " +
"REFERENCES " + PhotoEntry.TABLE_NAME + "(" + PhotoEntry._ID + ") " +
")";
public static final String SQL_CREATE_EVENT =
"CREATE TABLE " + EventEntry.TABLE_NAME + " (" +
EventEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
EventEntry.COLUMN_NAME_ALBUM_ID + " INTEGER, " +
EventEntry.COLUMN_NAME_TITLE + " TEXT, " +
EventEntry.COLUMN_NAME_SUBTITLE + " TEXT, " +
"FOREIGN KEY (" + EventEntry.COLUMN_NAME_ALBUM_ID + ") " +
"REFERENCES " + AlbumEntry.TABLE_NAME + "(" + AlbumEntry._ID + ") " +
")";
public static final String SQL_CREATE_ALBUM =
"CREATE TABLE " + AlbumEntry.TABLE_NAME + " (" +
AlbumEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
AlbumEntry.COLUMN_NAME_TITLE + " TEXT, " +
AlbumEntry.COLUMN_NAME_SUBTITLE + " TEXT)";
}
The app lets the user store captions/descriptions to images on the device, so if the user annotates an image, then the image ID + caption is stored in the photo table. There is a 1:n relationship to the stack table, where several images can be part of a "stack". Futhermore, sequences of photos (assuming strictly increasing/consecutive IDs) can be grouped as an event. And several events can be grouped as an album. I'm trying to formalize this using foreign key constraints.
But I want to start small, with just the photo table and get that to work :) My question is: How do I get off on the right leg with migrations, as in onUpgrade() etc? I guess the first migration is going from no database to setting one up?
public class MyappDbHelper extends SQLiteOpenHelper {
// If you change the database schema, you must increment the database version.
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "Myapp.db";
public MyappDbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
//db.execSQL(AlbumContract.SQL_CREATE_ALBUM); // I'm starting with just the PHOTO and STACK tables
//db.execSQL(AlbumContract.SQL_CREATE_EVENT);
db.execSQL(AlbumContract.SQL_CREATE_PHOTO);
db.execSQL(AlbumContract.SQL_CREATE_STACK);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//db.execSQL(SQL_DELETE_ENTRIES);
onCreate(db);
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
onUpgrade(db, oldVersion, newVersion);
}
}
It seems you are trying to use old approach to create SQLite database. If you use Room library to work with SQLite, then you must create @Entity and @Dao(Data Access Object) classes for your data, and the @Database class which extends RoomDatabase.
For your case code looks like this:
@Entity
public class Photo {
@PrimaryKey
public int photoId;
@ColumnInfo(name = "mediastoreUri")
public String mediastoreUri;
@ColumnInfo(name = "description")
public String description;
@ColumnInfo(name = "photoEventId")
public long photoEventId;
}
@Entity
public class Event {
@PrimaryKey
public int eventId;
@ColumnInfo(name = "title")
public String title;
@ColumnInfo(name = "subtitle")
public String subtitle;
}
// One-to-Many relationship
public class EventWithPhotos {
@Embedded
public Event event;
@Relation(
parentColumn = "eventId",
entityColumn = "photoEventId"
)
public List<Photo> photos;
}
@Dao
public interface PhotoDao {
@Query("SELECT * FROM Photo")
List<Photo> getAll();
@Query("SELECT * FROM Photo WHERE photoId IN (:ids)")
List<Photo> loadAllByIds(int[] ids);
@Insert
void insertAll(Photo... photos);
@Delete
void delete(Photo photo);
}
@Database(entities = {Photo.class, Event.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
public abstract PhotoDao userDao();
}
For more details see: Room overview, Relationships in Room, Migrations in Room