Android Studio 菜鸟笔记本-Day 29-介绍Room资料库三种类别

Room

今天会介绍Android里的Room资料库中的类别有

• Entity
• DAO
• Database

Entity

建立资料库的表格

//@Entity标注用来表示资料库的表格，并且tableName设置表格名称
@Entity(tableName = "MyUser")
public class User {
    //@PrimaryKey标示这是一个主键，其属性autoGenerate设置是否使ID自动累加
    @PrimaryKey(autoGenerate = true)
    private int id;
    private String name;
    private String phone;
    private String hobby;

    public User( String name, String phone, String hobby) {
        this.name = name;
        this.phone = phone;
        this.hobby = hobby;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

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

    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getHobby() {
        return hobby;
    }
    public void setHobby(String hobby) {
        this.hobby = hobby;
    }
}

DAO(Data Access Object)

DAO是设置SQL语法的地方，里面包含了最常见的 CURD(Create, Update, Read, Delete)方法。

public interface UserDao {
    String tableName="MyUser";
    //新增所有资料
    @Insert(onConflict = OnConflictStrategy.REPLACE)//预设万一执行出错时，REPLACE为覆盖
    void insertData(User player);
    //捞取全部资料
    @Query("SELECT * FROM "+ tableName)
    List<User> getAllUsers();
    //更新资料
    @Update
    void updateData(User player);
    //删除资料
    @Query(" DELETE  FROM " + tableName + " WHERE id = :id")
    void deleteData(int id);
}

在此可以使用@Insert、@Update、@Delete以及@Query等SQL语法。

Database

继承RoomDatabase，并建立abstract class的资料库

//@Database的entities:之前创建的data.class，version:资料库版本，exportSchema:是否将资料导出至文件
@Database(entities = { User.class }, version = 1, exportSchema = false)
public abstract class UserDataBase extends RoomDatabase {

    private static final String DB_NAME ="UserDataBase.db";//资料库名称
    private static volatile UserDataBase instance;
    //使用synchronized能够确保在同一个时间只有一个 Thread 进入UserDataBase
    public static synchronized UserDataBase getInstance( Context context){
        if (instance == null) {
            instance = create(context);//创立新的资料库
        }
        return instance;
    }
    private static UserDataBase create(final Context context){
        return Room.databaseBuilder(context,UserDataBase.class,DB_NAME).build();
    }
    public abstract UserDao getUserDao();//创建DAO的抽象类
}

介绍Room资料库三种类别就到此，谢谢大家。