如何在运行时动态查询会议室数据库? [英] How to dynamically query the room database at runtime?

问题描述

是否可以在运行时构造查询?

Is it possible construct a query at runtime?

@Query("SELECT * FROM playlist " +
        "WHERE playlist_title LIKE '% :playlistTitle %' " +
        "GROUP BY playlist_title " +
        "ORDER BY playlist_title " +
        "LIMIT :limit")
 List<IPlaylist> searchPlaylists(String playlistTitle, int limit);

limit部分是可选的.也就是说，它应该能够执行相同的查询而不受限制.

The limit part is optional. That is, it should be able to perform the same query with or without limit.

在前一种情况下，可以进行两个带有和不带有限制部分的静态查询，并且每次都可以使用一个适当的查询.但是有时我们可能不得不处理更复杂的情况，例如构建过滤器.

In the previous case, it is possible to make two static queries with and without limit part and appropriate one can be used each time. But sometimes we may have to deal with more complex situations like building a filter.

在这种情况下，与前面的示例不同，它将有多个可选部分.对于一张书，我们可能需要根据该书所属的类别，作者姓名，价格范围，出版日期等进行过滤.几乎不可能用这些部分的所有组合进行静态查询.

In that case, unlike the previous example, there will be multiple number of optional parts. For a table of books, we may need to do filtering according to the category the book belongs to, author name, price range, publication date etc. It is almost impossible to make static queries with all combinations of these parts.

推荐答案

在我的使用Room的经验(简短)中，这是不可能的，并且不是因为Room限制，而是@CommonsWare隐式评论了SQLite的限制.您需要两个查询，因此在您的DAO中需要两个方法.

In my experience (short) using Room that's not possible, and not because of being a Room limitation but, as implicitly commented by @CommonsWare , a limitation on SQLite. You need two queries, and therefore two methods in your DAO.

我会有类似的东西

@Query("SELECT * FROM playlist " +
    "WHERE playlist_title LIKE '% :playlistTitle %' " +
    "GROUP BY playlist_title " +
    "ORDER BY playlist_title " +
    "LIMIT :limit")
List<IPlaylist> searchPlaylists(String playlistTitle, int limit);

@Query("SELECT * FROM playlist " +
    "WHERE playlist_title LIKE '% :playlistTitle %' " +
    "GROUP BY playlist_title " +
    "ORDER BY playlist_title ")
List<IPlaylist> searchPlaylists(String playlistTitle);

然后在其他地方绕过:

if (limit.isPresent()) {
   return playlistDao.searchPlaylists(title, limit.get());
} else {
   return playlistDao.searchPlaylists(title);
}

这是我目前能想到的最佳选择.

That 's the best option I can think at the moment.

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