Android Room的学习之基本使用

Room学习三部曲

Android Room的学习之基本使用
Android Room的学习之关联表
Android Room的学习之数据库升级

最近实际开发中有用到数据库，所以就抽时间研究下 Room官方地址

1. 简介
   Room是一个对象关系映射(ORM)库。
   Room抽象了SQLite的使用，可以在充分利用SQLite的同时访问流畅的数据库。
   

2. Room的组成
   Database
   Entity
   DAO
   Database：app持久化状态，并作为与应用持久关联数据的底层连接的主要访问点。
   使用Database注解的类需要满足的条件：

   1. 集成RoomDatabase的抽象类
   2. 包含与数据库相关联的实体列表。
   3. 包含一个无参抽象方法并且返回的类需要用@Dao注解

   Entity：用来注解实体类，并利用该类的所有字段作为表的列来创建表。
   Dao：提供访问数据库的方法。

使用：

1.添加依赖

   def room_version = "1.1.1"
   implementation "android.arch.persistence.room:runtime:$room_version"
    annotationProcessor "android.arch.persistence.room:compiler:$room_version"
    // optional - RxJava support for Room
    api "android.arch.persistence.room:rxjava2:$room_version"
    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "android.arch.persistence.room:guava:$room_version"
    // Test helpers
    testImplementation "android.arch.persistence.room:testing:$room_version"

Android x 使用

    def room_version = "2.2.1"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor

    // optional - Kotlin Extensions and Coroutines support for Room
    implementation "androidx.room:room-ktx:$room_version"

    // optional - RxJava support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"

    // Test helpers
    testImplementation "androidx.room:room-testing:$room_version"

2.例子

创建实体类 - Student.java

@Entity
public class Student {

    @PrimaryKey(autoGenerate = true)
    public int sId;

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

    @ColumnInfo(name = "age")
    public int age;

    public int getId() {
        return sId;
    }

    public void setId(int sId) {
        this.sId = sId;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

然后是StudentDao.java

@Dao
public interface StudentDao {

    @Query("SELECT * FROM Student")
    List<Student> getAll();

    @Query("SELECT * FROM Student WHERE sId IN (:userIds)")
    List<Student> loadAllByIds(int[] userIds);

    @Query("SELECT * FROM Student WHERE age=:age")
    List<Student> getStudentByAge(int age);

    @Query("SELECT * FROM Student WHERE age=:age LIMIT :max")
    List<Student> getStudentByAge(int max, int... age);

    @Query("SELECT * FROM Student WHERE sId =:sId")
    Student getStudent(int sId);

    @Insert
    void insertAll(Student... users);

    @Update
    void updateStudent(Student... users);

    @Delete
    void delete(Student user);

}

最后是 AppDatabase.java

@Database(entities = {Student.class}, version = 1,exportSchema = false)
public abstract class AppDatabase extends RoomDatabase {

    private static final String DB_NAME = "StudentDatabase.db";
    private static volatile AppDatabase instance;

    static synchronized AppDatabase getInstance(Context context) {
        if (instance == null) {
            instance = create(context);
        }
        return instance;
    }

    private static AppDatabase create(final Context context) {
        return Room.databaseBuilder(
                context,
                AppDatabase.class,
                DB_NAME).build();
    }

    public abstract StudentDao  studentDao();
}

重点 重点 重点： 所有数据库的操作都需要放在异步线程 最好与RxJava合用。

添加：

 StudentDao mStudentDao = AppDatabase.getInstance(this).studentDao();
 Student mStudent = new Student();
 mStudent.setId(id);
 mStudent.setAge(age);
 mStudent.setName(name);
 mStudentDao.insertAll(mStudent);

更新：

 StudentDao mStudentDao = AppDatabase.getInstance(this).studentDao();
 Student mStudent = new Student();
 mStudent.setId(1);
 mStudent.setAge(562);
 mStudent.setName("张三222");
 mStudentDao.updateStudent(mStudent);

删除：

 StudentDao mStudentDao = AppDatabase.getInstance(this).studentDao();
 Student mStudent = new Student();
 mStudent.setId(1);
 mStudent.setAge(56);
 mStudent.setName("张三");
 mStudentDao.delete(mStudent);

查找：

 StudentDao mStudentDao = AppDatabase.getInstance(this).studentDao();
List<Student> list =  mStudentDao.getAll()//查找全部

Student mStudent =  mStudentDao.getStudent(7)//根据年龄查找 返回对象

List<Student> list = mStudentDao.getStudentByAge(60)//根据年龄查找 list

List<Student> list = mStudentDao.getStudentByAge(60, 70)//根据年龄区间 查找 list

至此，简单的Room 数据库就完成了