Android ROOM的基本使用

Myth丶恋晨 2022-10-06 15:57 160阅读 0赞

# 简介 #

[Room][]持久库提供了一个SQLite抽象层，让你访问数据库更加稳如狗，提示数据库性能。  
Room库帮助应用数据缓存，这个缓存是应用唯一的真实来源，并且允许用户查看应用中的关键信息的一致副本。

# 导入库 #

dependencies {
        def room_version = "1.1.1"
    
        implementation "android.arch.persistence.room:runtime:$room_version"
        annotationProcessor "android.arch.persistence.room:compiler:$room_version" // use kapt for Kotlin
    
        // optional - RxJava support for Room
        implementation "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"
    }

在Androidx版本下

dependencies {
        def room_version = "2.0.0-beta01"
    
        implementation "androidx.room:room-runtime:$room_version"
        annotationProcessor "androidx.room:room-compiler:$room_version" // use kapt for Kotlin
    
        // 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"
    }

# ROOM的三个重要组件 #

[Database][]具体可看官网，用[@Database][Database]注解的类应该需要满足以下条件

*  一个继承[RoomDatabase][]的抽象类
 *  在注释中包含数据库相关联的实体列表
 *  在包含具有0个参数的抽象方法，并返回用[@Dao][Dao]

在运行时，可以通过调用[Room.databaseBuild()][Room.databaseBuild]或者[Room.inMemoryDatabaseBuild()][Room.inMemoryDatabaseBuild]  
获取数据库实例  
[Entity][]:表示数据库内的表  
[Dao][Dao 1]:包含用于访问数据库的方法。  
这些组件，以及它们与程序的其余部分的关系可自寻在网上找图图解.  
下面代码示例包含了entity与dao数据的配置  
kotlin写法

@Entity
    data class User(
            var userName: String,
    
            var passWord: String
    ) {
        @PrimaryKey
        var id = 0
    
    }

Java写法，参考

@Entity
    public class User {
        @PrimaryKey
        private int uid;
    
        @ColumnInfo(name = "first_name")
        private String firstName;
    
        @ColumnInfo(name = "last_name")
        private String lastName;
    
        // Getters and setters are ignored for brevity,
        // but they're required for Room to work.
    }

userDao.kt

@Dao
    interface UserDao {
        //查询user表中所有数据
        @get:Query("SELECT * FROM user")
        val all: List<User?>?
    
        @Query("SELECT * FROM user WHERE 'uid' IN (:userIds)")
        fun loadAllByIds(userIds: IntArray?): List<User?>?
    
        //    @Query("SELECT * FROM user   LIMIT 1")
        //    void findUser(User user);
    
        @Query("SELECT * FROM User LIMIT 1")
        fun findUser(): User?
    
        @Insert
        fun insertAll(users: User?)
    
        @Delete
        fun delete(vararg users: User?)
    
        @Query("DELETE FROM User")
        fun deleteAllUser()
    }

userDao.java

@Dao
    public interface UserDao {
        @Query("SELECT * FROM user")
        List<User> getAll();
    
        @Query("SELECT * FROM user WHERE uid IN (:userIds)")
        List<User> loadAllByIds(int[] userIds);
    
        @Query("SELECT * FROM user WHERE first_name LIKE :first AND "
               + "last_name LIKE :last LIMIT 1")
        User findByName(String first, String last);
    
        @Insert
        void insertAll(User... users);
    
        @Delete
        void delete(User user);
    }

AppDatabase .kt

@Database(entities = [User::class], version = 1)
    abstract class AppDatabase : RoomDatabase() {
        abstract fun userDao(): UserDao?
    }

AppDatabase.java

@Database(entities = {User.class}, version = 1)
    public abstract class AppDatabase extends RoomDatabase {
        public abstract UserDao userDao();
    }

在创建上面的文件之后，使用以下代码获得创建数据库的实例：

# kotlin #

var db: AppDatabase? = null
     db = Room.databaseBuilder(applicationContext,
                    AppDatabase::class.java, "database-name")
                    .allowMainThreadQueries() //允许在主线程中查询
                    .build()

# java #

AppDatabase db;
    db = Room.databaseBuilder(getApplicationContext(),
                    AppDatabase.class, "database-name")
                    .allowMainThreadQueries()//允许在主线程中查询
                    .build();

注意：在实例化AppDatabase对象时，应遵循单例设计模式，因为每个Roomdatabase实例都相当消耗性能，并且您很少需要访问多个实例。  
参考文章：[https://blog.csdn.net/u011897062/article/details/82107709][https_blog.csdn.net_u011897062_article_details_82107709]本人增加了kontlin写法

作者：枫叶豆腐汤  
链接：https://www.jianshu.com/p/82a06f579e52  
来源：简书  
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

[Room]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Ftraining%2Fdata-storage%2Froom%2Findex.html
[Database]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Freference%2Fandroid%2Farch%2Fpersistence%2Froom%2FDatabase.html
[RoomDatabase]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Freference%2Fandroid%2Farch%2Fpersistence%2Froom%2FRoomDatabase.html
[Dao]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Freference%2Fandroid%2Farch%2Fpersistence%2Froom%2FDao.html
[Room.databaseBuild]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Freference%2Fandroid%2Farch%2Fpersistence%2Froom%2FRoom.html%23databaseBuilder%2528android.content.Context%2C%2520java.lang.Class%253CT%253E%2C%2520java.lang.String%2529
[Room.inMemoryDatabaseBuild]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Freference%2Fandroid%2Farch%2Fpersistence%2Froom%2FRoom.html%23inMemoryDatabaseBuilder%2528android.content.Context%2C%2520java.lang.Class%253CT%253E%2529
[Entity]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Ftraining%2Fdata-storage%2Froom%2Fdefining-data.html
[Dao 1]: https://links.jianshu.com/go?to=https%3A%2F%2Fdeveloper.android.google.cn%2Ftraining%2Fdata-storage%2Froom%2Faccessing-data.html
[https_blog.csdn.net_u011897062_article_details_82107709]: https://links.jianshu.com/go?to=https%3A%2F%2Fblog.csdn.net%2Fu011897062%2Farticle%2Fdetails%2F82107709