Android Room框架使用

介绍

Room在SQLite之上提供了一个抽象层，可以在使用SQLite的全部功能的同时流畅访问数据库。

• @Database: @Database用来注解类，并且注解的类必须是继承自RoomDatabase的抽象类。该类主要作用是创建数据库和创建Daos（data access objects，数据访问对象）。

• @Entity: @Entity 用来注解实体类， @Database 通过entities属性引用被 @Entity注解的类，并利用该类的所有字段作为表的列名来创建表。

• @Dao： @Dao用来注解一个接口或者抽象方法，该类的作用是提供访问数据库的方法。在使用 @Database注解的类中必须定一个不带参数的方法，这个方法返回使用 @Dao注解的类。

应用

Android TV APP，给客户做一个EPG功能模块，可以预约EPG。

• 导入Room库

allprojects {
    repositories {
    jcenter()
    maven {url 'https://maven.google.com' }
    }
}


// Room Persistence Library
compile 'android.arch.persistence.room:runtime:1.0.0'
annotationProcessor 'android.arch.persistence.room:compiler:1.0.0'

• 创建表(表名、字段根据注释一目了然)

@Entity(tableName = "epg")
public class EPG {

    public EPG(String program, int channelID, String start, String end) {
        this.program = program;
        this.channelID = channelID;
        this.start = start;
        this.end = end;
    }

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "epgProgram")
    @SerializedName("epgProgram")
    private String program;

    @ColumnInfo(name = "epgChannelID")
    @SerializedName("epgChannelID")
    private int channelID;

    @ColumnInfo(name = "epgStart")
    @SerializedName("epgStart")
    private String start;

    @ColumnInfo(name = "epgEnd")
    @SerializedName("epgEnd")

//set、get方法省略
...
}

@Entity(tableName = "bookprogram")
public class BookProgram {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "channel")
    @SerializedName("channel")
    private String channel;

    @ColumnInfo(name = "program")
    @SerializedName("program")
    private String program;

    @ColumnInfo(name = "starttamp")
    @SerializedName("starttamp")
    private Long starttamp;

    @ColumnInfo(name = "streamUrl")
    @SerializedName("streamUrl")
    private String streamUrl;

//set、get方法省略
...
}

• DAO类

@Dao
public interface EpgDAO {

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

    @Query("SELECT * FROM epg where epgChannelID = :channelid AND epgEnd > :timestamp AND epgStart < :timestamp ORDER BY epgEnd ASC LIMIT 1")
    EPG findNowByChannel(int channelid, long timestamp);

    @Query("SELECT * FROM epg where epgChannelID = :channelid AND epgStart > :timestamp ORDER BY epgEnd ASC LIMIT 1")
    EPG findNextByChannel(int channelid, long timestamp);

    @Query("SELECT * FROM epg where epgChannelID = :channelid ORDER BY epgEnd")
    List<EPG> findEPGByChannel(int channelid);

    @Query("SELECT COUNT(*) from epg")
    int countEPGs();

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertAll(EPG... epgs);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertAll(List<EPG> epgs);

    @Delete
    void delete(EPG epg);

    @Query("DELETE FROM epg")
    void clearAll();
}

@Dao
public interface BookProgramDAO {

    @Query("SELECT * FROM bookprogram")
    List<BookProgram> getAllBookProgram();

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertBookProgram(BookProgram bookProgram);

    @Query("DELETE FROM bookprogram WHERE program = :program AND starttamp = :starttamp")
    void deleteBookProgram(String program,long starttamp);

    @Query("DELETE FROM bookprogram")
    void clearAll();
}

• Database类

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

    private static AppDatabase INSTANCE;

    public abstract EpgDAO epgDao();

    public abstract BookProgramDAO bookProgramDao();

    public static AppDatabase getAppDatabase(Context context) {
        if (INSTANCE == null) {
            INSTANCE =
                Room.databaseBuilder(context.getApplicationContext(), AppDatabase.class, "itvdatabase")
                        // allow queries on the main thread.
                        // Don't do this on a real app! See PersistenceBasicSample for an example.
                        .allowMainThreadQueries()
                        .fallbackToDestructiveMigration()
                        .build();
        }
        return INSTANCE;
    }


    public static void destroyInstance() {
        INSTANCE = null;
    }
}

使用时获取AppDatabse单例，调用成员DAO的接口即可