Jetpack ROOM使用示例

module 下build.gradle 配置 schemas 

  defaultConfig {
        
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation":
                                     "$projectDir/schemas".toString()]
            }
        }


    }

1. 实体@Entity 映射到表

@Entity(tableName = "users")
public class User {

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "user_id")
    private int userId;

    @ColumnInfo(name = "user_name")
    private String name;

    @ColumnInfo(name = "user_address",defaultValue = "四川省成都市")
    private String address;

    @ColumnInfo(name = "user_age")
    private int age;



    public User(int userId, String name, String address, int age) {
        this.userId = userId;
        this.name = name;
        this.address = address;
        this.age = age;

    }


    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

2. Dao

@Dao
public interface UserDao {


    @Query("select * from users")
    List<User> getAllUsers();

    @Query("select * from users where user_id = :id")
    User getUserById(int id);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertUser(User userModel);

    @Query("update users set user_name = :name AND user_age = :age WHERE user_id = :id")
    void updateUser(int id, String name, String age);

    @Update(onConflict =  OnConflictStrategy.REPLACE)
    void updateUsers(User... users);

    @Query("delete from users where user_id = :id")
    void deleteUserById(int id);

    @Delete
    void deleteUsers(User... users);

}

3. DataBase

@Database(entities = {User.class, Student.class}, version = 1)
public abstract class UserDataBase extends RoomDatabase {

    private static UserDataBase instance;
    private static final String DB_NAME = "mydata.db";

    public static UserDataBase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),UserDataBase.class, DB_NAME)
                 
                    .allowMainThreadQueries()
                    .build();
        }
        return instance;
    }

   


    public abstract UserDao userDao();

    public abstract StudentDao studentDao();

}

4. 使用

UserDao userDao =  UserDataBase.getInstance(MainActivity.this).userDao();
userDao.insertUser(new User("gali"+i,"四川成都"+i,2*i,"男"));
List<User> data =  userDao.getAllUsers();

5.如果更新表 User新加一个字段

@Entity(tableName = "users")
public class User {

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "user_id")
    private int userId;

    @ColumnInfo(name = "user_name")
    private String name;

    @ColumnInfo(name = "user_address",defaultValue = "四川省成都市")
    private String address;

    @ColumnInfo(name = "user_age")
    private int age;

   @ColumnInfo(name = "user_sex")
   private String sex;

    public User( String name, String address, int age,String sex) {

        this.name = name;
        this.address = address;
        this.age = age;
        this.sex = sex;
    }

    
}

@Database(entities = {User.class, Student.class}, version = 2)
public abstract class UserDataBase extends RoomDatabase {

    private static UserDataBase instance;
    private static final String DB_NAME = "mydata.db";

    public static UserDataBase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),UserDataBase.class, DB_NAME)
                    .addMigrations(MIGRATION_1_2)
                 
                    .allowMainThreadQueries()
                    .build();
        }
        return instance;
    }

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



    public abstract UserDao userDao();

    public abstract StudentDao studentDao();

   
}

6. 如果再新加一个表

@Entity(tableName = "persons")
public class Person {

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "person_id")
    int personId;


    @ColumnInfo(name = "person_name")
    String name;


    public Person(String name) {
        this.name = name;
    }

}

@Dao
public interface PersonDao {

    @Query("select * from persons")
    List<Person> getAllPerson();

    @Query("select * from persons where person_id = :id")
    Person getPersonById(int id);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertPerson(Person userModel);

}

@Database(entities = {User.class, Student.class,Person.class}, version = 3)
public abstract class UserDataBase extends RoomDatabase {

    private static UserDataBase instance;
    private static final String DB_NAME = "mydata.db";

    public static UserDataBase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),UserDataBase.class, DB_NAME)
                    .addMigrations(MIGRATION_1_2)
                    .addMigrations(MIGRATION_2_3)
                    .allowMainThreadQueries()
                    .build();
        }
        return instance;
    }

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

    public static Migration MIGRATION_2_3 = new Migration(2,3) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("create table persons(person_id INTEGER primary key autoincrement not null,person_name TEXT ) ");
        }
    };


    public abstract UserDao userDao();

    public abstract StudentDao studentDao();

    public abstract PersonDao personDao();
}