ROOM 数据库的使用
相关用法请看Google
ROOM 数据库查看内容
sqlitebrowser 用这个查看数据库的数据
开发中遇到的问题点
单元测试会在Device File Explorer -》 data/data/包名.text 中
数据库升级的坑
fallbackToDestructiveMigration()。将会删除数据库并重建
vesion增加，提供Migration - 数据正常
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase database) {
// 因为没有变化，所以是一个空实现
}
};
改表结构
static final Migration MIGRATION_2_3 = new Migration(2, 3) {
@Override
public void migrate(SupportSQLiteDatabase database) {
database.execSQL("ALTER TABLE users "
+ " ADD COLUMN last_update INTEGER");
}
};
复杂的Migration
static final Migration MIGRATION_3_4 = new Migration(3, 4) {
@Override
public void migrate(SupportSQLiteDatabase database) {
// 创建临时表
database.execSQL(
"CREATE TABLE users_new (userid TEXT, username TEXT, last_update INTEGER, PRIMARY KEY(userid))");
// 拷贝数据
database.execSQL(
"INSERT INTO users_new (userid, username, last_update) SELECT userid, username, last_update FROM users");
// 删除老的表
database.execSQL("DROP TABLE users");
// 改名
database.execSQL("ALTER TABLE users_new RENAME TO users");
}
};
常用注解
常用SQL语句
//增加新字段
database.execSQL("ALTER TABLE user ADD age INTEGER Default 0 not null ")
//创建新的数据表
database.execSQL("CREATE TABLE temp_Student (" +
"id INTEGER PRIMARY KEY NOT NULL," +
"name TEXT," +
"age TEXT)");
// 拷贝数据
database.execSQL("INSERT INTO temp_Student (id, name, age) " +
"SELECT id, name, age FROM Student");
// 删除老的表
database.execSQL("DROP TABLE Student");
// 改名
database.execSQL("ALTER TABLE temp_Student RENAME TO Student");
//模糊查询
@Query("SELECT * FROM owner WHERE room_id LIKE '%' || :roomId || '%'")
fun getAllOwnerByRoomId(roomId: String): List<Owner>
@Query("SELECT * FROM user WHERE age BETWEEN :minAge AND :maxAge")
public User[] loadAllUsersBetweenAges(int minAge, int maxAge);