Android Room 數據庫

刪除表 "drop table if exists " + TABLE_NAME
刪除數據不刪表 "DELETE FROM " + TABLE_NAME

解決Schema export Error:
Schema export directory is not provided to the annotation processor so we cannot export the schema.
You can either provide room.schemaLocation annotation processor argument OR set exportSchema to false.

解決方式一：
給RoomDatabase設置exportSchema註解爲false。

@Database(entities = { YourEntity.class }, version = xxx, **exportSchema = false**)
public abstract class AppDatabase extends RoomDatabase {
}

解決方案二：
在項目中gradle中通過 annotationProcessorOptions 註解，爲room.schemaLocation指定schemas的子文件夾。

android {
    defaultConfig {
        //指定room.schemaLocation生成的文件路徑
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
            }
        }
    }
}

使用步驟：
1、創建實體類，註解規則

@Entity	//數據表名稱
public class User {

    @PrimaryKey(autoGenerate = true)	//主鍵，自增
    private long uid;
    private String name;
    private String address;
    private String phone;
    private Integer age;

    public User(String name, String address, String phone) {
        this.name = name;
        this.address = address;
        this.phone = phone;
    }
  	...
  	
    @Override
    public String toString() {
        return "User{" +
                "uid=" + uid +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", phone='" + phone + '\'' +
                ", age=" + age +
                '}';
    }
}

2、創建Dao接口

@Dao
public interface UserDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)  //指明衝突解決方案
    List<Long> insert(User... user);

    @Query("Select * from user")
    Flowable<List<User>> loadUser();

    @Query("delete from user where user.name=:uid")  //根據條件刪除
    void delete(String uid);

    @Update(onConflict = OnConflictStrategy.REPLACE)
    void update(User user);

    @Query("delete from user")   //刪除全部信息
    void deletAll();

}

3、自定義database，繼承roomdatabase

@Database(entities = {User.class,Book.class},version = 3,exportSchema = false)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
    public abstract BookDao bookDao();
}

4、Applacation初始化數據庫

public class AppApplication extends AppContext {
    private AppDatabase mAppDatabase;

    @Override
    public void onCreate() {
        super.onCreate();

        mAppDatabase = Room.databaseBuilder(getApplicationContext(), AppDatabase.class, "android_room_test.db")
                .allowMainThreadQueries()
                .addMigrations(MIGRATION_1_2, MIGRATION_2_3)
                .build();
    }

    public AppDatabase getmAppDatabase() {
        return mAppDatabase;
    }

    static final Migration MIGRATION_2_3 = new Migration(2, 3) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("create table if not exists 'book'('uid'integer primary key autoincrement,'name' text,'userid' integer,'time' integer)");
        }
    };

    static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("alter table User add column age integer");
        }
    };
}

5、使用

 case R.id.buttonadd:
                int index= (int)(Math.random()*10);
                User user=new User("frank"+index,"address"+index,"176xxxxxxxx"+index);
                mAppDatabase.userDao().insert(user);
                showResult.setText("插入數據："+user.toString());
                break;
            case R.id.buttondel:
                int index1= (int)(Math.random()*10);
                long index2= (long)(Math.random()*100);
                User user1=new User("frank"+index1,"address"+index1,"176xxxxxxxx"+index1);
                mAppDatabase.userDao().delete(user1.getName());
                showResult.setText("刪除數據name："+user1.getName());
                break;
            case R.id.buttonquery:
                mAppDatabase.userDao().loadUser().subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new Consumer<List<User>>() {
                            @Override
                            public void accept(List<User> users) throws Exception {
                                if (users!=null){
                                    container.removeAllViews();
                                    for (User user:users){
                                        TextView v=new TextView(TestRoomActivity.this);
                                        v.setText("查詢數據："+user.toString());
                                        container.addView(v);
                                    }
                                }
                            }
                        });
                break;
            case R.id.buttonupdate:
                mAppDatabase.userDao().deletAll();
                break;