有什么办法可以在房间数据库中运行嵌套查询 [英] is there any way to run nested query in room database
问题描述
我正在将旧的Android
项目迁移到新标准,我陷入了room database
之间,无法找到如何使用room database
执行这2个SQLite
命令的情况.我有2个以嵌套方式工作的查询,因此使用room
达到相同的结果是有可能的.
I am migrating my old Android
project to new standards, I got stuck in between room database
, not able to find how to execute these 2 SQLite
commands using room database
. I have 2 queries which are working in a nested manner, so to achieve the same result using room
is there any possibility.
default public ArrayList getOfflineRoomsAndObjectsByParentIds(String parentId, String site_id, Context context) {
databaseHandler = new DatabaseHandler(context);
Cursor cr = null;
ArrayList<Room> offlineRoomNamesList = new ArrayList<>();
try {
**sqLiteDatabase = databaseHandler.getReadableDatabase();
String query = "SELECT * FROM " + Constants.TABLE_ROOM_NAMES
+ " WHERE " + Constants.SITE_ID + " = '" + site_id + "' AND " + Constants.PARENT_ID + "='" + parentId + "'";**
cr = sqLiteDatabase.rawQuery(query, null);
if (cr.moveToFirst()) {
do {
Room room = new Room();
**room.setId(cr.getString(cr.getColumnIndex(Constants.KEY_ROOM_ID)));
query = "SELECT * FROM " + Constants.TABLE_OFFLINE_ROOM_OBJECTS
+ " WHERE " + Constants.KEY_ROOM_KEY + " = ?"
+ " AND " + Constants.SITE_ID + " = ? ORDER BY " + Constants.KEY_OBJECT_NAME;**
Cursor cursor = sqLiteDatabase.rawQuery(query, new String[]{cr.getString(cr.getColumnIndex(Constants.KEY_ROOM_KEY)), site_id});
if (cursor.moveToFirst()) {
do {
RoomObject roomObject = new RoomObject();
roomObject.setRoomKey(cursor.getString(cursor.getColumnIndex(Constants.KEY_ROOM_KEY)));
roomObject.setId(cursor.getInt(cursor.getColumnIndex(Constants.KEY_ID)));
roomObject.setInstanceNumber(cursor.getInt(cursor.getColumnIndex(Constants.KEY_INSTANCE_NUMBER)));
roomObject.setObjectType(cursor.getString(cursor.getColumnIndex(Constants.KEY_OBJECT_TYPE)));
String mergeKey = AppSharedPreference.getString(AppSharedPreference.MERGE_KEY, "", context);
if (roomObject.getObjectName().contains(mergeKey) && !TextUtils.isEmpty(mergeKey)) {
room.addMergeableObjectsInList(roomObject);
} else {
room.addRoomObjectsInList(roomObject);
}
}
while (cursor.moveToNext());
}
if (room.getRoomObjectsList().size() > 0)
offlineRoomNamesList.add(room);
cursor.close();
} while (cr.moveToNext());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
cr.close();
sqLiteDatabase.close();
} catch (Exception e) {
e.printStackTrace();
}
}
return offlineRoomNamesList;
}
此刻我所看到的唯一可能性是两个定义2个不同的查询并以嵌套方式执行它们.
The only possibility I am looking at this moment is two define 2 different query and execute them into a nested manner.
@Dao
public interface ControllerRoomObjectDao {
@Query("SELECT * FROM room_names WHERE site_id=:siteId AND parentId=:parentId")
Single<List<Room>>getOfflineRoomsAndObjectsByParentId(String siteId, String parentId);
@Query("SELECT * FROM offline_objects WHERE site_id=:siteId AND parentId=:parentId")
Single<List<RoomObject>>getOfflineObjectsByParentId(String siteId, String parentId);
}
推荐答案
不确定这是否完全符合您的要求,但可能会帮助具有相同一般要求的其他人.
Not sure if this meets your requirements exactly, but it may help others with the same general requirement.
基本上,我从此示例获取了建议,该示例显示了如何执行嵌套MySQL中的查询/子查询.
Basically, I took the advice from this example that shows how to perform a nested query / subquery in MySQL.
使用相同的语法,我可以从以下方式更改我的基本DAO查询:
With that same syntax I was able to change my basic DAO query from:
@Transaction
@Query("SELECT * FROM `events` WHERE `item_id` = :currentItemId AND `event_datetime` > :datetimeFrom ORDER BY `event_datetime` ASC LIMIT 1")
LiveData<Event> getNextEventWithSameItemId(long currentItemId, String datetimeFrom);
到
@Transaction
@Query("SELECT * FROM `events` WHERE `item_id` IN (SELECT `item_id` FROM `events` WHERE `_id` = :currentEventId) AND `event_datetime` > :datetimeFrom ORDER BY `event_datetime` ASC LIMIT 1")
LiveData<Event> getNextEventWithSameEventId(long currentEventId, String datetimeFrom);
我的事件实体所在的位置
@Entity(tableName = "events")
public class Event {
@PrimaryKey
@ColumnInfo(name = "_id")
public long id;
@ColumnInfo(name = "item_id") // Relates to `items`.`_id`
public long itemId;
@ColumnInfo(name = "event_datetime")
public String eventDatetime;
...
}
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