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Android Room Persistance Library

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我是Room的新手，而@Relation对我来说并不清楚 . 如果我理解正确，我有实体，例如（RSS）ChannelEntity，channel有名为ItemEntity的项目 . 这些是带有@Entity注释的类 . 我也有一个POJO来“连接”我的entites . 我的意思是我要像这样写一个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
}

我要编写一个dao界面，我可以像这样得到Channel（不是ChannelEntity）：

public interface ChannelDao {

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

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

通过这些实体，DAO和POJO，我可以获得包含具有相应链接（id）的Items列表的Channel对象 . 是对的吗？

我的另一个问题是关于其余的CRUD . 例如 . 如果我想保存一个新 Channels ，我可以将此声明添加到我的ChannelDao吗？

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

删除

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

等等 . 那么它会从传递的Channel对象中创建和删除ChannelEntities和ItemEntities吗？

android android-room

1 回答

  • 1

    我更新了我的课程，因为@CommonsWare提供了建议 . 现在我有@Embedded对象的实体类：

    @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
}

    其中一个嵌入式类：

    // 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;
}

    我已经为所有类编写了带有@Entity注释的daos（我称之为嵌入式类实体，即使它们不是，但我有视图的模型类，我不想在以后混淆它们） .

    我映射了这样的关系：

    // 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

    当我想获得一个包含项目列表的 Channels 时，我会这样：

    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Channel的道：

    @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();
}
    回复于

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