Android Room Persistance Library

Question

我是新来的房间，而@Relation对我来说还不清楚。 如果我理解正确，我有实体例如（RSS）ChannelEntity，并且频道具有名为ItemEntity的项目。 这些是带有@Entity注解的类。 我也有一个POJO来“连接”我的实体。我的意思是我写这样一个POJO：

public class Channel { 

    @Embedded 
    private ChannelEntity channel; 

// Link is the primary key in ChannelyEntity 
    @Relation (parentColumn = "link", entityColumn = "channel_link") 
    private ArrayList<ItemEntity> items; 

// Getters and Setters are here 
} 

比我写这样的DAO接口在哪儿能买到通道（未ChannelEntity）：

public interface ChannelDao { 

    @Query("SELECT * FROM channels WHERE link = :link LIMIT 1") 
    Channel getChannelById(String link); 

    @Query("SELECT * FROM channels") 
    ArrayList<Channel> getAllChannels(); 
} 

与这些实体，DAO和POJO我可以获得Channel对象，其中包含具有相应链接（id）的Items列表。是对的吗？

我的其他问题是有关其余CRUD的问题。例如。如果我想保存一个新频道，我可以将此声明添加到我的ChannelDao中吗？

@Insert(onConflict = OnConflictStrategy.REPLACE) 
void createChannels(Channel... channels); 

删除

@Delete 
void deleteChannels(Channel... channels); 

等。那么它会从传递的Channel对象创建并删除ChannelEntities和ItemEntities？

Answer 1

我更新了我的课程，作为@CommonsWare提供了它。 现在我有@Embedded对象实体类：

@Entity (tableName = "channels") 
public class ChannelEntity { 
    // Required channel elements 
    // The name of the channel. It's how people refer to your service. 
    private String title; 
    // The URL of the HTML website corresponding to the channel 
    @PrimaryKey 
    private String link; 
    //other fileds 
    @Embedded 
    private TextInputEntity textInputEntity; 
    @Embedded 
    private ImageEntity imageEntity; 
    //getters and setters 
} 

一个嵌入式类：

// Specifies a text input box displayed with the channel. 
// Embedded in ChannelEntity 
public class TextInputEntity { 
    // Required elements 
    // The label of the Submit button in the text input area. 
    private String title; 
    // Explains the text input aera. 
    private String description; 
    // The name of the text object int hte text input area. 
    private String name; 
    // The URL of the CGI script that processes the text input request 
    private String link; 
    @ColumnInfo (name = "channel_link") 
    private String channelLink; 
} 

我写的daos所有的班级有@Entity批注（我称为嵌入式类实体甚至他们不是，但我有模型类的意见，我不想混淆他们以后）。

我这样映射关系：

// All items are optional, but at least one of title or description must be presented. 
@Entity (tableName = "items" 
     , foreignKeys = @ForeignKey (entity = Channel.class 
     , parentColumns = "link" 
     , childColumns = "channel_link")) 
public class ItemEntity { 
    @PrimaryKey (autoGenerate = true) 
    private int id; 
    // Title of the item 
    private String title; 
    // Other fileds 
    @ColumnInfo (name = "channel_link") 
    private String channelLink; 
    // Getters and setters 

当我想要得到一个通道与项目列表中，我得到这样的：

public class Channel { 
    @Embedded 
    private ChannelEntity channel; 
    @Relation (parentColumn = "link", entityColumn = "channel_link") 
    private ArrayList<ItemEntity> items; 
    @Relation (parentColumn = "link", entityColumn = "channel_link") 
    private ArrayList<SkipDayEntity> skipDays; 
    @Relation (parentColumn = "link", entityColumn = "channel_link") 
    private ArrayList<SkipHourEntity> skipHours; 
//Setters and getters 
} 

这是海峡道：

@Dao 
public interface ChannelDao { 
    @Insert (onConflict = OnConflictStrategy.REPLACE) 
    void insertChannel(ChannelEntity channel); 

    @Update 
    void updateChannel(ChannelEntity channel); 

    @Delete 
    void deleteChannel(ChannelEntity channel); 

    @Query ("SELECT * FROM channles WHERE link = :link LIMIT 1") 
    Channel getChannelByLink(String link); 

    @Query ("SELECT * FROM channels") 
    LiveData<ArrayList<Channel>> getAllChannels(); 
}