1. 在 Room (三) 基础上做更改
2. 添加数据库字段
2.1 Word 类修改,添加字段
@Entity
public class Word {
@PrimaryKey(autoGenerate = true)
private int id; //主键
@ColumnInfo(name = "english_word")
private String word;
@ColumnInfo(name = "chinese_meaning")
private String chineseMeaning;
@ColumnInfo(name = "foo_data")
private boolean foo;
@ColumnInfo(name = "bar_data")
private boolean bar;
public Word(String word, String chineseMeaning) {
this.word = word;
this.chineseMeaning = chineseMeaning;
}
public boolean isBar() {
return bar;
}
public void setBar(boolean bar) {
this.bar = bar;
}
public boolean isFoo() {
return foo;
}
public void setFoo(boolean foo) {
this.foo = foo;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getWord() {
return word;
}
public void setWord(String word) {
this.word = word;
}
public String getChineseMeaning() {
return chineseMeaning;
}
public void setChineseMeaning(String chineseMeaning) {
this.chineseMeaning = chineseMeaning;
}
}
2.2 WordDatabase 管理数据上修改,升级版本
//singleton 只允许生成一个实例
@Database(entities = {Word.class}, version = 3, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
private static WordDatabase INSTANCE;
//synchronized: 解决多个线程下调用,创建多个实例问题
static synchronized WordDatabase getDatabase(Context context) {
if (INSTANCE == null) {
//fallbackToDestructiveMigration 把当前的数据清空,创建新的库
//addMigrations 添加迁移的策略
INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
.addMigrations(migration_2_3)
.build();
}
return INSTANCE;
}
public abstract WordDao getWordDao();
//添加字段操作
static final Migration migration_2_3 = new Migration(2, 3) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
database.execSQL("ALTER TABLE word ADD COLUMN bar_data INTEGER NOT NULL DEFAULT 1");
}
};
}
3. 删除数据库字段
3.1 Word 类,删除字段
@Entity
public class Word {
@PrimaryKey(autoGenerate = true)
private int id; //主键
@ColumnInfo(name = "english_word")
private String word;
@ColumnInfo(name = "chinese_meaning")
private String chineseMeaning;
// @ColumnInfo(name = "foo_data")
// private boolean foo;
// @ColumnInfo(name = "bar_data")
// private boolean bar;
public Word(String word, String chineseMeaning) {
this.word = word;
this.chineseMeaning = chineseMeaning;
}
// public boolean isBar() {
// return bar;
// }
//
// public void setBar(boolean bar) {
// this.bar = bar;
// }
//
// public boolean isFoo() {
// return foo;
// }
//
// public void setFoo(boolean foo) {
// this.foo = foo;
// }
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getWord() {
return word;
}
public void setWord(String word) {
this.word = word;
}
public String getChineseMeaning() {
return chineseMeaning;
}
public void setChineseMeaning(String chineseMeaning) {
this.chineseMeaning = chineseMeaning;
}
}
3.2 WordDatabase 类做修改,升级版本
//singleton 只允许生成一个实例
@Database(entities = {Word.class}, version = 4, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
private static WordDatabase INSTANCE;
//synchronized: 解决多个线程下调用,创建多个实例问题
static synchronized WordDatabase getDatabase(Context context) {
if (INSTANCE == null) {
//fallbackToDestructiveMigration 把当前的数据清空,创建新的库
//addMigrations 添加迁移的策略
INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
.addMigrations(migration_3_4)
.build();
}
return INSTANCE;
}
public abstract WordDao getWordDao();
//删除字段操作
static final Migration migration_3_4 = new Migration(3, 4) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
database.execSQL("CREATE TABLE word_temp (id INTEGER PRIMARY KEY NOT NULL , english_word TEXT," +
"chinese_meaning TEXT)");
database.execSQL("INSERT INTO word_temp (id,english_word,chinese_meaning) " +
"SELECT id,english_word,chinese_meaning FROM word");
database.execSQL("DROP TABLE word");
database.execSQL("ALTER TABLE word_temp RENAME to word");
}
};
}
4. 执行效果是否成功
查看 Device File Explorer -> data -> data ->com.xx.xx(应用包名) -> database -> xx_database(自己定义的数据库名称),导出以 .db 命名保存,以浏览数据库应用查看表(Navicat Premium)。