--Create an entity class with @ Entity.
--Create a class that operates entities with @Dao.
--Create a class that inherits RoomDatabase and register the class with @ Dao as its member.
--Operate a class that inherits RoomDatabase from the app
Note that classes that inherit from RoomDatabase cannot be operated on the main thread.
@ Entity class@Entity(indices = {@Index(value = {"name"}, unique = true)})
public class User {
@PrimaryKey
public long id;
@ColumnInfo
public String name;
}
@Dao class example@Dao
public abstract class UserDao {
@Query("select id from user order by id desc limit 1")
public abstract long getMaxId();
@Insert(onConflict = OnConflictStrategy.IGNORE)
abstract void insert(User user);
@Query("delete from user where id = :id")
abstract void delete(long id);
}
RoomDatabase Inheritance class example@Database(entities = {User.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
public abstract UserDao userDao();
}
public class AppDatabaseSingleton {
private static AppDatabase instance = null;
private AppDatabaseSingleton() {}
public static AppDatabase getInstance(Context context) {
if (instance != null) {
return instance;
}
instance = Room.databaseBuilder(context,
AppDatabase.class, "app_database").build();
return instance;
}
}
new Thread(new Runnable() {
@Override
public void run() {
AppDatabase db = AppDatabaseSingleton.getInstance(context);
long maxId = db.UserDao().getMaxId();
callback.onComplete(maxId);
}
}).start();
Write in @ Entity like(tableName = {"table name"). If you do not specify it, the table will be created with the same name as the model name, so it is better to specify it if possible.
@Entity(tableName = "users")
public class User {
@PrimaryKey
public int id;
@ColumnInfo(name = "first_name")
public String firstName;
@ColumnInfo(name = "last_name")
public String lastName;
}
Write @Ignore before the column name.
@Entity
public class User {
@PrimaryKey
public int id;
public String firstName;
public String lastName;
@Ignore
Bitmap picture;
}
Write (indeces = {@Index (value = {"first column "," second column "}, unique = true)}) in @ Entity.
@Entity(indices = {@Index(value = {"first_name", "last_name"},
unique = true)})
public class User {
@PrimaryKey
public int id;
@ColumnInfo(name = "first_name")
public String firstName;
@ColumnInfo(name = "last_name")
public String lastName;
}
Write separated by commas
@Entity(tableName = "users",
indices = {@Index(value = {"first_name", "last_name"},
unique = true)})
First of all, as a basic thing, issue a query with @Dao instead of @Entity.
Add (onConflict = OnConflictStrategy.IGNORE) to @ Insert.
If you want to replace it, use (onConflict = OnConflictStrategy.REPLACE).
@Dao
public interface MyDao {
@Insert(onConflict = OnConflictStrategy.IGNORE)
public void insertUsers(User... users);
@Insert(onConflict = OnConflictStrategy.REPLACE)
public void insertBothUsers(User user1, User user2);
@Insert
public void insertUsersAndFriends(User user, List<User> friends);
}
If you want to make a transaction, you need to change from ʻinterface to ʻabstract class.
Then, specify @Transaction as the target method.
@Dao
abstract class UsersDao {
@Transaction
public void setLoggedInUser(User loggedInUser) {
deleteUser(loggedInUser);
insertUser(loggedInUser);
}
@Query("DELETE FROM users")
abstract void deleteUser(User user);
@Insert
abstract void insertUser(User user);
}
Raise the version as in SQLite. If you just raise it, nothing will be done, so you need to write what to do. If you don't write it, you will get angry.
A migration from 1 to 2 was required but not found. Please provide the necessary Migration path via RoomDatabase.Builder.addMigration(Migration ...) or allow for destructive migrations via one of the RoomDatabase.Builder.fallbackToDestructiveMigration* methods.
The error message kindly tells you what to do, so in short, just do it.
For example, if you upgrade to version 3, add a Fruit table in version 2, and add a column of Integer called pub_year to the Book table in version 3, you get:
@Database(entities = {Fruit.class, Book.class}, version = 3)
public abstract class AppDatabase extends RoomDatabase {
:
public static AppDatabase getInstance(Context context) {
if (instance != null) {
return instance;
}
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
database.execSQL("CREATE TABLE `Fruit` (`id` INTEGER, "
+ "`name` TEXT, PRIMARY KEY(`id`))");
}
};
static final Migration MIGRATION_2_3 = new Migration(2, 3) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
database.execSQL("ALTER TABLE Book "
+ " ADD COLUMN pub_year INTEGER");
}
};
instance = Room.databaseBuilder(context,
AppDatabase.class, "database-name")
.addMigrations(MIGRATION_1_2, MIGRATION_2_3)
.build();
return instance;
}
}
I'd like you to wrap this area well, but at the moment there is a sense of human power.
It may be relatively easy to use the table creation SQL etc. as it is with reference to the expanded room.
For example, if you have created an inherited class for RoomDatabase with the class name com.example.db.AppDatabase, then ʻapp / build / generated / source / apt / debug / com / example / db / AppDatabase_Impl.java The contents expanded to are output. The following is an example of ʻAppDatabase_Impl.
@SuppressWarnings({"unchecked", "deprecation"})
public final class AppDatabase_Impl extends AppDatabase {
@Override
protected SupportSQLiteOpenHelper createOpenHelper(DatabaseConfiguration configuration) {
final SupportSQLiteOpenHelper.Callback _openCallback = new RoomOpenHelper(configuration, new RoomOpenHelper.Delegate(2) {
@Override
public void createAllTables(SupportSQLiteDatabase _db) {
_db.execSQL("CREATE TABLE IF NOT EXISTS `Fruit` (`id` INTEGER NOT NULL, `name` TEXT, PRIMARY KEY(`id`))");
:
}
:
}
}
}
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