Question

我在Room DAO中有一个查询，该查询（针对提供的countryId）查询我的share_groups表，并返回包含num_twitter_users数字（通过计算数字来计算）的行share_group_individuals表中填充的行数）。

这是查询的代码：

@Query("SELECT `share_groups`.`_id`, `share_group_name`, `share_group_description`, `share_group_instructions`, `share_group_order`, `share_group_is_visible`, `share_groups`.`last_modified`" +

    // `num_twitter_users` will contain the number of share_group_individuals within this share_group that have a Twitter username.
    ", COUNT(DISTINCT(CASE WHEN (`share_group_individuals`.`share_group_individual_twitter` IS NOT NULL AND `share_group_individuals`.`share_group_individual_twitter` != '') THEN `share_group_individuals`.`_id` ELSE NULL END)) AS `num_twitter_users`" +

    " FROM `share_groups`" +

    // Join with `share_group_individuals` - on countryId
    " LEFT JOIN `share_group_individuals` ON (`share_group_individuals`.`share_group_id` = `share_groups`.`_id`" +
    " AND `share_group_individuals`.`share_group_individual_country_id` = :countryId)" +

    // Search on countryId
    " WHERE `share_group_individuals`.`share_group_individual_country_id` = :countryId" +

    " GROUP BY `share_groups`.`share_group_name`, `share_group_individuals`.`share_group_id`" +

    // Only return share_groups that contain at least 1 share_group_individual with a Twitter account
    " HAVING `num_twitter_users` > 0" +

    " ORDER BY `share_group_order` ASC")
LiveData<List<ShareGroup>> getAllShareGroups(long countryId);

但是，我无法从返回的num_twitter_users中访问LivaData<List<ShareGroup>>的值。

我想知道解决方案的一部分是否可能是创建一个ShareGroupWithData POJO（并因此从我的查询中返回一个LivaData<List<ShareGroupWithData>>），但是，如果这是正确的方法，我将如何填充numTwitterUsers类中的ShareGroupWithData变量？

我在网上或official documentation上都找不到任何信息，因此朝正确的方向和/或一些示例代码表示感谢。

为完整起见，此实体代表的我的share_groups表：

@Entity(tableName = "share_groups")
public class ShareGroup {

    @PrimaryKey
    @ColumnInfo(name = "_id")
    private long id;

    @NonNull
    @ColumnInfo(name = "share_group_name")
    private String shareGroupName;

    @ColumnInfo(name = "share_group_description")
    private String shareGroupDescription;

    @ColumnInfo(name = "share_group_instructions")
    private String shareGroupInstructions;

    @ColumnInfo(name = "share_group_order", defaultValue = "10")
    private int shareGroupOrder;

    @ColumnInfo(name = "share_group_is_visible", defaultValue = "1")
    private boolean shareGroupIsVisible;

    @ColumnInfo(name = "last_modified")
    private long lastModified;

...
}

我的share_groups_individual表由该实体表示：

@Entity(tableName = "share_group_individuals",
        indices = {@Index(name = "index_share_group_id", value = "share_group_id")},
        foreignKeys = @ForeignKey(entity = ShareGroup.class, parentColumns = "_id", childColumns = "share_group_id", onDelete = ForeignKey.CASCADE)
)
public class ShareGroupIndividual {

    @PrimaryKey
    @ColumnInfo(name = "_id")
    private long id;

    @ColumnInfo(name = "share_group_id")
    private long shareGroupId;

    @ColumnInfo(name = "share_group_individual_country_id", defaultValue = "-1")
    private long shareGroupIndividualCountryId;

    @ColumnInfo(name = "share_group_individual_name")
    private String shareGroupIndividualName;

    @ColumnInfo(name = "share_group_individual_twitter")
    private String shareGroupIndividualTwitter;

...
}

Answer 1

最后，我通过创建这样的POJO来解决了这个问题：

public class ShareGroupWithData {

    @Embedded
    public ShareGroup shareGroup;

    @ColumnInfo(name = "num_twitter_users", defaultValue = "0")
    public int numTwitterUsers;
...
}

我的DAO代码更改为：

LiveData<List<ShareGroupWithData>> getAllShareGroupsWithData(long countryId);

Room-如何从DAO查询中获取COUNT值？

1 个答案: