Android Room的學習之數據庫升級

Room學習三部曲

Android Room的學習之基本使用
Android Room的學習之關聯表
Android Room的學習之數據庫升級

Room的數據庫升級分爲兩種：

1. 清空數據庫中的數據（不建議使用）

private static AppDatabase create(final Context context) {
        return Room.databaseBuilder(
                context,
                AppDatabase.class,
                DB_NAME)
                //添加fallbackToDestructiveMigration方法
                .fallbackToDestructiveMigration()
                .build();

2. 在原有數據的基礎上，添加自己想要的數據

 private static AppDatabase create(final Context context) {
        return Room.databaseBuilder(
                context,
                AppDatabase.class,
                DB_NAME)
                 //添加addMigrations方法
                .addMigrations(MIGRATION_1_4)
                .build();

1. 在原有表的基礎上添加新的字段

      
   
   @Database(entities = {Student.class}, version = 2, exportSchema = false)
     public abstract class AppDatabase extends RoomDatabase {
   
     static Migration MIGRATION_1_2 = new Migration(1, 2) {
           @Override
           public void migrate(SupportSQLiteDatabase database) {
               // 爲舊錶添加新的字段
               database.execSQL("ALTER TABLE Student "
                       + " ADD COLUMN  sex INTEGER NOT NULL DEFAULT 0");
           }
       };
   
     private static AppDatabase create(final Context context) {
       return Room.databaseBuilder(
               context,
               AppDatabase.class,
               DB_NAME)
                //添加addMigrations方法
               .addMigrations(MIGRATION_1_2)
               .build();
       }
   

2. 添加新的表

   
    @Database(entities = {Student.class}, version = 4, exportSchema = false)
     public abstract class AppDatabase extends RoomDatabase {
   
     static Migration MIGRATION_1_4= new Migration(1, 4) {
       @Override
       public void migrate(SupportSQLiteDatabase database) {
           // 爲舊錶添加新的字段
           database.execSQL("ALTER TABLE Student "
                       + " ADD COLUMN  sex INTEGER NOT NULL DEFAULT 0");
           //  添加新的表
           database.execSQL("CREATE TABLE IF NOT EXISTS Book (bookName TEXT, studentId TEXT, bookId PRIMARY KEY )");
   
       }
   };
   
     private static AppDatabase create(final Context context) {
           return Room.databaseBuilder(
                   context,
                   AppDatabase.class,
                   DB_NAME)
                    //添加addMigrations方法
                   .addMigrations(MIGRATION_1_4)
                   .build();
   }
   

遇見的問題：

android Room 升級 java.lang.IllegalStateException: Migration didn't properly handle

這裏是升級數據庫遇到的，添加新的字段類似

sex INTEGER NOT NULL DEFAULT 0

一定要有默認值

TableInfo{name='Book', columns={studentId=Column{name='studentId', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0, defaultValue='null'}, bookName=Column{name='bookName', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0, defaultValue='null'}, bookId=Column{name='bookId', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}
     Found:
TableInfo{name='Book', columns={studentId=Column{name='studentId', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, bookName=Column{name='bookName', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0, defaultValue='null'}, bookId=Column{name='bookId', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}

查看不一樣的改成一樣的