Android Room 数据库

删除表 "drop table if exists " + TABLE_NAME
删除数据不删表 "DELETE FROM " + TABLE_NAME

解决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.

解决方式一：
给RoomDatabase设置exportSchema注解为false。

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

解决方案二：
在项目中gradle中通过 annotationProcessorOptions 注解，为room.schemaLocation指定schemas的子文件夹。

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

使用步骤：
1、创建实体类，注解规则

@Entity//数据表名称public class User {    @PrimaryKey(autoGenerate = true)//主键，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、创建Dao接口

@Daopublic interface UserDao {    @Insert(onConflict = OnConflictStrategy.REPLACE)  //指明冲突解决方案    List insert(User... user);    @Query("Select * from user")    Flowable> loadUser();    @Query("delete from user where user.name=:uid")  //根据条件删除    void delete(String uid);    @Update(onConflict = OnConflictStrategy.REPLACE)    void update(User user);    @Query("delete from user")   //删除全部信息    void deletAll();}

3、自定义database，继承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初始化数据库

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("插入数据："+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("删除数据name："+user1.getName());                break;            case R.id.buttonquery:                mAppDatabase.userDao().loadUser().subscribeOn(Schedulers.io())                        .observeOn(AndroidSchedulers.mainThread())                        .subscribe(new Consumer>() {                            @Override                            public void accept(List users) throws Exception {                                if (users!=null){                                    container.removeAllViews();                                    for (User user:users){                                        TextView v=new TextView(TestRoomActivity.this);                                        v.setText("查询数据："+user.toString());                                        container.addView(v);                                    }                                }                            }                        });                break;            case R.id.buttonupdate:                mAppDatabase.userDao().deletAll();                break;

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