我有三个表,一个表包含Cards,一个表包含CardDecks,第三个表实现前两个表之间的多对多关系,并为每个关系条目都包含一个符号。
我的任务是从卡片表中获取三列,从关系表中获取符号,并将其保存在专门设计用于处理这些输入的数据对象中,条件是所有条目均与给定的deckId匹配。或使用(希望是正确的)sql语言:
@Query("SELECT R.symbol, C.title, C.type, C.source " +
"FROM card_table C JOIN cards_to_card_deck R ON C.id = R.card_id"+
"WHERE R.card_deck_id = :cardDeckId")
LiveData<List<CardWithSymbol>> getCardsWithSymbolInCardDeckById(long cardDeckId);
但是房间实现类会生成:
@Override
public LiveData<List<CardWithSymbol>> getCardsWithSymbolInCardDeckById(long
cardDeckId) {
final String _sql = "SELECT R.symbol, C.title, C.typ, C.source FROM
cards_to_card_deck R INNER JOIN card_table C ON R.card_id = C.id WHERE
R.card_deck_id = ?";
final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 1);
int _argIndex = 1;
_statement.bindLong(_argIndex, cardDeckId);
return new ComputableLiveData<List<CardWithSymbol>>() {
private Observer _observer;
@Override
protected List<CardWithSymbol> compute() {
if (_observer == null) {
_observer = new Observer("cards_to_card_deck","card_table") {
@Override
public void onInvalidated(@NonNull Set<String> tables) {
invalidate();
}
};
__db.getInvalidationTracker().addWeakObserver(_observer);
}
final Cursor _cursor = __db.query(_statement);
try {
final int _cursorIndexOfSymbol = _cursor.getColumnIndexOrThrow("symbol");
final List<CardWithSymbol> _result = new ArrayList<CardWithSymbol>(_cursor.getCount());
while(_cursor.moveToNext()) {
final CardWithSymbol _item;
final int _tmpSymbol;
_tmpSymbol = _cursor.getInt(_cursorIndexOfSymbol);
_item = new CardWithSymbol(_tmpSymbol,null,null,null);
_result.add(_item);
}
return _result;
} finally {
_cursor.close();
}
}
@Override
protected void finalize() {
_statement.release();
}
}.getLiveData();
}
哪里
_item =新的CardWithSymbol(_tmpSymbol,null,null,null);
应该返回我完全初始化的对象。
CardWithSymbol类的声明如下:
public class CardWithSymbol {
public int symbol;
public String cardName;
public String cardType;
public String cardSource;
public CardWithSymbol(int symbol, String cardName, String cardType, String cardSource){
this.symbol = symbol;
this.cardName = cardName;
this.cardType = cardType;
this.cardSource = cardSource;
}
查询返回的列的类型为:
int符号,字符串标题,字符串类型,字符串源
我已经进行了一些调试,该应用程序的其余部分工作正常。我什至可以从查询返回的对象中读取符号,但是如上所述,出于某种原因,room忽略了其他三个参数,只是在查询实现中将它们默认为null。
答案 0 :(得分:0)
因此,经过反复试验并再次阅读dao文档,我发现了自己的错误:
在创建用于处理会议室中的列子集的类时,重要的是要通过@ColumnInfo(name = "name of the column goes here")
注释告诉会议室哪个变量对应于哪些列。
因此,如下更改CardWithSymbol类可以为我解决问题:
import android.arch.persistence.room.ColumnInfo;
public class CardWithSymbol {
@ColumnInfo(name = "symbol")
public int symbol;
@ColumnInfo(name = "title")
public String cardName;
@ColumnInfo(name = "type")
public String cardType;
@ColumnInfo(name = "source")
public String cardSource;
public CardWithSymbol(int symbol, String cardName, String cardType, String cardSource){
this.symbol = symbol;
this.cardName = cardName;
this.cardType = cardType;
this.cardSource = cardSource;
}
}