以录入书籍信息为例，使用Room框架的编码过程分为下列五步：

1、编写书籍信息表对应的实体类，该类添加“@Entity”注解

package com.example.study_android.entity;

import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class BookInfo {
    @PrimaryKey(autoGenerate = true)
    private int id;

    public String name;
    public String author;
    public double price;

    @Override
    public String toString() {
        return "BookInfo{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                '}';
    }
}

2、编写书籍信息表对应的持久化类，该类添加“@Dao”注解

@Dao
public interface BookDao {
    @Insert
    void insert(BookInfo... book);

    @Delete
    void delete(BookInfo... book);

    @Query("DELETE FROM BookInfo")
    void deleteAll();

    @Update
    int update(BookInfo... book);

    @Query("SELECT * FROM BookInfo")
    List<BookInfo> queryAll();

    @Query("SELECT * FROM BookInfo WHERE name=:name ORDER BY id DESC limit 1")
    BookInfo queryByName(String name);
}

3、编写书籍信息表对应的数据库类，该类从RoomDatabase派生而来，并添加“@Database”注解

package com.example.study_android.database;

import androidx.room.Database;
import androidx.room.RoomDatabase;

import com.example.study_android.dao.BookDao;
import com.example.study_android.entity.BookInfo;

@Database(entities = {BookInfo.class}, version = 1, exportSchema = true)
public abstract class BookDatabase extends RoomDatabase {

    // 获取该数据库中某张表的持久化对象
    public abstract BookDao bookDao();
}

• entities：表示该数据库有哪些表
• exportSchema：表示是否导出数据库信息的json串，建议设为false，若设为true还需指定json文件的保存路径

在build.gradle中添加导出路径

        javaCompileOptions {
            annotationProcessorOptions {
                //指定数据库schema导出的位置
                arguments += mapOf(
                    "room.schemaLocation" to "$projectDir/schemas",
                    "room.incremental" to "true"
                )
            }
        }

4、在自定义的Application类中声明书籍数据库的唯一实例

public class MyApplication extends Application {
    private static MyApplication mApp;

    // 声明一个书籍数据库对象
    private BookDatabase bookDatabase;

    public static MyApplication getInstance() {
        return mApp;
    }

    // App启动时调用
    @Override
    public void onCreate() {
        super.onCreate();
        mApp = this;

        // 构建书籍数据库的实例
        bookDatabase = Room.databaseBuilder(this, BookDatabase.class, "'book")
                // 允许迁移数据库（发生数据库变更时，Room默认删除原数据库再创建新数据库，如此一来原来的记录会丢失，故而要改为迁移方式以便保存原有记录）
                .addMigrations()
                // 允许主线程中操作数据库（Room默认不能在主线程中操作数据库）
                .allowMainThreadQueries()
                .build();
    }

    public BookDatabase getBookDB() {
        return bookDatabase;
    }
}

5、在操作书籍信息表的地方获取数据表的持久化对象

bookDao = MyApplication.getInstance().getBookDB().bookDao();

@Override
    public void onClick(View view) {
        String name = et_book_name.getText().toString();
        String author = et_author.getText().toString();
        String price = et_price.getText().toString();

        switch (view.getId()) {
            case R.id.btn_save:
                BookInfo book = new BookInfo();
                book.name = name;
                book.author = author;
                book.price = Double.parseDouble(price);
                bookDao.insert(book);
                ToastUtil.show(this, "保存成功");
                break;
            case R.id.btn_del:
                BookInfo b2 = new BookInfo();
                b2.id = 1;
                bookDao.delete(b2);
                break;
            case R.id.btn_edit:
                BookInfo b3 = new BookInfo();
                BookInfo b4=bookDao.queryByName(name);

                b3.id = b4.id;
                b3.name = name;

                bookDao.update(b3);
                break;
            case R.id.btn_query:
                List<BookInfo> list = bookDao.queryAll();
                StringBuilder sb = new StringBuilder();

                for (BookInfo b : list) {
                    sb.append(b.toString());
                }
                tv_result.setText(sb);
                break;
        }
    }

案例代码