手摸手教你在Room中使用List
实际项目有很多这样的结构:
{
"id": "001",
"name": "王诛魔",
"age": 2018,
"books": [
{
"bookId": 10081,
"userId": 1,
"book": "断罪小学",
"desc": "漫画讲述了李杀神、王诛魔和刘斩仙三位少年，为了十万小学生的未来、为了改变被诅咒的命运，相聚在狼牙区飞虎路私立断罪小学，誓死打败四年级的魔神赵日天的故事。"
},
{
"bookId": 10088,
"userId": 1,
"book": "狂霸天下之断罪学园",
"desc": "《狂霸天下之断罪学园》，后来因为名字太长，而且“学园”和“学院”容易混淆的原因而改名。"
}
]
}
也就是,类似books这样的,List
下面就以上面的结构为例,做一个简单的演示,按照最简答的方法实现.
1.添加依赖
https://developer.android.google.cn/topic/libraries/architecture/adding-components.html
值得注意的是,如果你在kotlin中使用
apply plugin: 'kotlin-kapt'
...
dependencies{
...
//这个无法生成代码,要用下面的那一条,不要疏忽忘掉了.
//annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
kapt "android.arch.persistence.room:compiler:1.0.0"
}
一定记得使用kapt,要不然就会遇到这个BUG.
2.创建表
-
User.java表
/** * If you have any questions, you can contact by email { [email protected]} * @author 王诛魔 2018/1/3 下午1:31 */ @Entity(tableName = "users") public class User { @PrimaryKey public int id; public String name; public int age; }@Entity 中指定了表名
@PrimaryKey 主键
这张表users 用于保存用户数据
-
Book.java表
/** * If you have any questions, you can contact by email { [email protected]} * @author 王诛魔 2018/1/3 下午1:30 */ @Entity(foreignKeys = { @ForeignKey( entity = User.class, parentColumns ={"id"}, childColumns = {"userId"}) },tableName = "books") public class Book { @PrimaryKey public int bookId; public int userId;//同User.java中的id public String book; public String desc; }@Entity 中
- foreignKeys = {} 中外键,可以是多个,这里只关联了User表
- tableName = "books" 指定了表名
@PrimaryKey 该表主键
-
UserAndBook.java表 ----UserAndBook只是辅助,不作为一张表存在.
/** * If you have any questions, you can contact by email { [email protected]} * @author 王诛魔 2018/1/3 下午1:43 */ public class UserAndBook { @Embedded //请看之前的文章,这是指把User中所有元素带入到这里作为元素存在 public User userEntity; //@Relation @Relation(parentColumn = "id",entityColumn = "userId",entity = Book.class) public Listbooks; } @Embedded 请看另一篇,有解释
@Relation 点这里去看官方文档
A convenience annotation which can be used in a Pojo to automatically fetch relation entities. When the Pojo is returned from a query, all of its relations are also fetched by Room.
个人以为就是一注解,指明关系,可以把实体关联起来,然后自动组装起来.
并且在文档中还展示了一种高端的功能,用上面做例
//@Relation @Relation(parentColumn = "id",entityColumn = "userId", entity = Book.class ,projection = {"book"}) public ListbookNames; 解释一下,projection指定了要取出的值,当前指明要在 books表中寻找符合条件parentColumn = "id",entityColumn = "userId" 的项,找到之后会拿到book这个值并返回.
3.Dao实现
/**
* If you have any questions, you can contact by email { [email protected]}
* @author 王诛魔 2018/1/3 下午4:20
*/
@Dao
public abstract class UserAndBookDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
public abstract void insert(User user);
@Insert(onConflict = OnConflictStrategy.REPLACE)
public abstract void insert(List books);
@Transaction
public void insert(UserAndBook userAndBook){
insert(userAndBook.userEntity);
insert(userAndBook.books);
}
@Query("SELECT * FROM users")
public abstract List getAll();
}
insert(User user); ,insert(List
两个方法,也可以私有化,只对外提供insert(UserAndBook userAndBook)
最近换公司项目的数据库,用sql,真的有意思,可以很方便的实现很多功能
4.建立数据库
/**
* If you have any questions, you can contact by email { [email protected]}
* @author 王诛魔 2017/10/24 上午10:13
* 数据库
*/
@Database(entities = {Book.class, User.class},
version = 1, exportSchema = false)
public abstract class AppDB extends RoomDatabase {
private static final String TAG = "AppDB";
/**
* 数据库实例
*/
private static AppDB sInstance;
private static String DATABASE_NAME = "developer.db";
private ObservableBoolean mIsDatabaseCreated = new ObservableBoolean(false);
public abstract UserAndBookDao userbook();
/**
* 单例
* @param context
* @return
*/
public static AppDB getInstance(Context context) {
if (sInstance == null) {
synchronized (AppDB.class) {
if (sInstance == null) {
sInstance = buildDatabase(context);
sInstance.updateDatabaseCreated(context);
}
}
}
return sInstance;
}
/**
* Build the database.
* creates a new instance of the database.
*/
private static AppDB buildDatabase(Context appContext) {
AppDB appDB = Room.databaseBuilder(appContext, AppDB.class, DATABASE_NAME)
.addCallback(new Callback() {
@Override
public void onCreate(@NonNull SupportSQLiteDatabase db) {
super.onCreate(db);
AppDB database = AppDB.getInstance(appContext);
database.setDatabaseCreated();
}
@Override
public void onOpen(@NonNull SupportSQLiteDatabase db) {
super.onOpen(db);
Log.e(TAG, "onOpen: " + db.getPath());
}
}).build();
return appDB;
}
/**
* Check whether the database already exists and expose it via
*/
private void updateDatabaseCreated(final Context context) {
if (context.getDatabasePath(DATABASE_NAME).exists()) {
setDatabaseCreated();
}
}
private void setDatabaseCreated() {
mIsDatabaseCreated.set(true);
}
public ObservableBoolean getDatabaseCreated() {
return mIsDatabaseCreated;
}
}
为了方便使用,在Application中添加了
public static AppDB getDatabase() {
return AppDB.getInstance(context);
}
5.使用
这里的使用方式,不建议使用,太粗暴了.
可以学学Demo,Google出的googlesamples/android-architecture-components
class RoomActivity : BindingActivity() {
val gson = Gson()
override fun getBundle(extras: Bundle) {
}
override fun layoutID(): Int = R.layout.activity_room
override fun initViews(savedInstanceState: Bundle?) {
//点击事件 ADD按钮,添加数据到数据库
mBindingView.button.setOnClickListener({
val userBook = UserAndBook()
val jsonStr = FileUtils.getJson(this, "data.txt")
val objectJson = JsonParser().parse(jsonStr).asJsonObject
//获取用户
val user = objectJson.get("user")
userBook.userEntity = gson.fromJson(user, User::class.java)
//保存用户
Observable
.empty()
.observeOn(Schedulers.io())
.subscribe(object : EmptyObserver() {
override fun onComplete() {
App.getDatabase().userbook().insert(userBook.userEntity)
}
})
//获取书籍
val books = objectJson.get("books")
userBook.books = gson.fromJson>
(books, object : TypeToken>() {}.type)
//保存书籍
Observable
.empty()
.observeOn(Schedulers.io())
.subscribe(object : EmptyObserver() {
override fun onComplete() {
App.getDatabase().userbook().insert(userBook.books)
}
})
})
//点击事件,按钮QUERY 查询数据
mBindingView.button2.setOnClickListener {
Flowable.create(FlowableOnSubscribe> { e ->
val userBook = App.getDatabase().userbook().all
e.onNext(userBook)
e.onComplete()
}, BackpressureStrategy.DROP)
.compose(DatabaseTransformer())
.subscribe(object : DatabaseSubscriber>() {
override fun onNext(userAndBooks: List) {
mBindingView.data = userAndBooks[0]
}
})
}
}
}