How to dynamically query the room database at runtime?
Room supports @RawQuery
annotation to construct queries at run-time.
Step 1 : Make DAO method
Mark the DAO method with @RawQuery
annotation instead of normal @Query
.
@Dao
interface BooksDao{
@RawQuery
List<Book> getBooks(SupportSQLiteQuery query);
}
Step 2 : Construct the query
Room uses prepared statements for security and compile time verification. Therefore, while constructing queries, we need to store query string and bind parameters separately.
In this example, I use the variable queryString
for query string and args
for bind parameters.
(Please note that I used text editor to write code. Therefore there may be typo or simple syntax errors. If you find anything please let me know in the comments or edit the post.)
// Query string
String queryString = new String();
// List of bind parameters
List<Object> args = new ArrayList();
boolean containsCondition = false;
// Beginning of query string
queryString += "SELECT * FROM BOOKS";
// Optional parts are added to query string and to args upon here
if(!authorName.isEmpty()){
queryString += " WHERE";
queryString += " author_name LIKE ?%";
args.add(authorName);
containsCondition = true;
}
if(fromDate!=null){
if (containsCondition) {
queryString += " AND";
} else {
queryString += " WHERE";
containsCondition = true;
}
queryString += " publication_date AFTER ?";
args.add(fromDate.getTime());
}
if(toDate!=null){
if (containsCondition) {
queryString += " AND";
} else {
queryString += " WHERE";
containsCondition = true;
}
queryString += " publication_date BEFORE ?";
args.add(toDate.getTime());
}
// End of query string
queryString += ";";
Step 3 : Perform query
SimpleSQLiteQuery query = new SimpleSQLiteQuery(queryString, args.toArray());
List<Book> result = booksDao.getBooks(query);
Notes
- Like normal
Query
,RawQuery
supports returning raw cursors, entities, POJOs and POJOs with embedded fields RawQuery
supports relations
Instead of writing multiple query i refer pass negative value to limit clause. Because if there is change in query i have to update the both query which is more error prone.
Official doc -> If the LIMIT expression evaluates to a negative value, then there is no upper bound on the number of rows returned. you can find it here https://sqlite.org/lang_select.html and read the limit clause section.
So I would do somthing like this,
@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);
and pass negative when you don't want to apply filter.
return playlistDao.searchPlaylists(title, limit.isPresent() ? limit.get() : -1)
It's working in my case.
Updated [21 Dec 2018]
In case If you are using kotlin use default value.
@JvmOverloads
@Query("SELECT * FROM playlist " +
"WHERE playlist_title LIKE '% :playlistTitle %' " +
"GROUP BY playlist_title " +
"ORDER BY playlist_title " +
"LIMIT :limit")
fun searchPlaylists(playlistTitle: String, limit: Int = -1): List<IPlaylist>
@JvmOverloads
to make it compatiable with Java. It generate two separate methods for Java.
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.
I would have something like:
@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);
Then somewhere else you do the bypass:
if (limit.isPresent()) {
return playlistDao.searchPlaylists(title, limit.get());
} else {
return playlistDao.searchPlaylists(title);
}
That's the best option I can think of at the moment.