Room的DAO实现未正确生成。

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英文:

Room's DAOimpl not generating correctly

问题

我正在尝试使用Room库访问数据库，但是DAO实现未生成好。
在我的DAO接口中，我有：

  1. @Query("SELECT b.position,b.name,b.capacity,b.currentAmount, it.name FROM bottles AS b " +
  2.         "INNER JOIN bottle_ingredient AS bi ON bi.bottlePos=b.position " +
  3.         "INNER JOIN ingredient_types AS it ON it.id=bi.ingredientId" +
  4.         " WHERE position = :position")
  5. Bottle getBottleWithIngredientFromPosition(int position);

而我的Bottle类如下：

  1. public class Bottle {
  2.     public int position;
  3.     public String name;
  4.     public int capacity;
  5.     public int currentAmount;
  6.     public String ingredientName;
  8.     //Constructor, getters and setters
  9. }

但是当我使用DAO创建一个新的Bottle对象时，它的"ingredientName"属性为空。我检查了Room生成的实现，如下所示：

  1. @Override
  2. public Bottle getBottleWithIngredientFromPosition(final int position) {
  3.     final String _sql = "SELECT b.position,b.name,b.capacity,b.currentAmount, it.name FROM bottles AS b INNER JOIN bottle_ingredient AS bi ON bi.bottlePos=b.position INNER JOIN ingredient_types AS it ON it.id=bi.ingredientId WHERE position = ?";
  4.     final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 1);
  5.     int _argIndex = 1;
  6.     _statement.bindLong(_argIndex, position);
  7.     __db.assertNotSuspendingTransaction();
  8.     final Cursor _cursor = DBUtil.query(__db, _statement, false, null);
  9.     try {
  10.         final int _cursorIndexOfPosition = 0;
  11.         final int _cursorIndexOfName = 1;
  12.         final int _cursorIndexOfCapacity = 2;
  13.         final int _cursorIndexOfCurrentAmount = 3;
  14.         final Bottle _result;
  15.         if(_cursor.moveToFirst()) {
  16.             final int _tmpPosition;
  17.             _tmpPosition = _cursor.getInt(_cursorIndexOfPosition);
  18.             final String _tmpName;
  19.             if (_cursor.isNull(_cursorIndexOfName)) {
  20.                 _tmpName = null;
  21.             } else {
  22.                 _tmpName = _cursor.getString(_cursorIndexOfName);
  23.             }
  24.             final int _tmpCapacity;
  25.             _tmpCapacity = _cursor.getInt(_cursorIndexOfCapacity);
  26.             final int _tmpCurrentAmount;
  27.             _tmpCurrentAmount = _cursor.getInt(_cursorIndexOfCurrentAmount);
  28.             _result = new Bottle(_tmpPosition,_tmpName,_tmpCapacity,_tmpCurrentAmount,null);
  29.         } else {
  30.             _result = null;
  31.         }
  32.         return _result;
  33.     } finally {
  34.         _cursor.close();
  35.         _statement.release();
  36.     }
  37. }

我们可以看到它调用构造函数时，最后一个参数为null，并且从数据库中获取该值的尝试。
我手动下载了SQLite数据库并运行了查询，它按预期工作。

英文:

I am trying to use Room library to access a DB, but DAO implementation is not generating well.
In my DAO interface i have:

  1.  @Query("SELECT b.position,b.name,b.capacity,b.currentAmount, it.name FROM bottles AS b " +
  2.             "INNER JOIN bottle_ingredient AS bi ON bi.bottlePos=b.position " +
  3.             "INNER JOIN ingredient_types AS it ON it.id=bi.ingredientId" +
  4.             " WHERE position = :position")
  5.     Bottle getBottleWithIngredientFromPosition(int position);

And my bottle class is the following:

  1. public class Bottle {
  2.     public int position;
  3.     public String name;
  4.     public int capacity;
  5.     public int currentAmount;
  6.     public String ingredientName;
  8.     //Constructor, getters and setters
  9. }

But when i create a new Bottle object with the DAO it gets created with "ingredientName" as null. I checked the implementation Room generates and is the following:

  1. @Override
  2.   public Bottle getBottleWithIngredientFromPosition(final int position) {
  3.     final String _sql = "SELECT b.position,b.name,b.capacity,b.currentAmount, it.name FROM bottles AS b INNER JOIN bottle_ingredient AS bi ON bi.bottlePos=b.position INNER JOIN ingredient_types AS it ON it.id=bi.ingredientId WHERE position = ?";
  4.     final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 1);
  5.     int _argIndex = 1;
  6.     _statement.bindLong(_argIndex, position);
  7.     __db.assertNotSuspendingTransaction();
  8.     final Cursor _cursor = DBUtil.query(__db, _statement, false, null);
  9.     try {
  10.       final int _cursorIndexOfPosition = 0;
  11.       final int _cursorIndexOfName = 1;
  12.       final int _cursorIndexOfCapacity = 2;
  13.       final int _cursorIndexOfCurrentAmount = 3;
  14.       final Bottle _result;
  15.       if(_cursor.moveToFirst()) {
  16.         final int _tmpPosition;
  17.         _tmpPosition = _cursor.getInt(_cursorIndexOfPosition);
  18.         final String _tmpName;
  19.         if (_cursor.isNull(_cursorIndexOfName)) {
  20.           _tmpName = null;
  21.         } else {
  22.           _tmpName = _cursor.getString(_cursorIndexOfName);
  23.         }
  24.         final int _tmpCapacity;
  25.         _tmpCapacity = _cursor.getInt(_cursorIndexOfCapacity);
  26.         final int _tmpCurrentAmount;
  27.         _tmpCurrentAmount = _cursor.getInt(_cursorIndexOfCurrentAmount);
  28.         _result = new Bottle(_tmpPosition,_tmpName,_tmpCapacity,_tmpCurrentAmount,null);
  29.       } else {
  30.         _result = null;
  31.       }
  32.       return _result;
  33.     } finally {
  34.       _cursor.close();
  35.       _statement.release();
  36.     }
  37.   }

As we can see it calls the constructor with last parameter as null and never tries to get it from the DB.
I downloaded SQLite DB and run the query manually and it works as espected

答案1

得分: 1

尝试使用以下查询：

  1. SELECT b.position, b.name, b.capacity, b.currentAmount, it.name AS ingredientName FROM ....
  • 其中 .... 是查询的其余部分。即，重要的部分是将 name 列别名为 ingredientName，使用 AS。

即，您提供的值可以/将与 ingredientName 成员变量关联。

这是假设您希望从 ingredient_types 表中获取 name 列的值作为 ingredientName。

英文:

Try SELECT b.position,b.name,b.capacity,b.currentAmount, it.name AS ingredientName FROM ....

  • where .... is the rest of the query. i.e. the important part is aliasing the name column to be ingredientName using AS.

i.e. you are supplying the value that can/will be associated with the ingredientName member variable.

This is assuming that you want the value of the name column from the ingredient_types table to be the ingredientName.

huangapple
  • 本文由 发表于 2023年5月21日 23:22:48
  • 转载请务必保留本文链接：https://go.coder-hub.com/76300620.html
  • android
  • android-room
  • java
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