我无法映射此SQLite查询的结果。在java中可以做到这一点吗？ DAO: @查询（“按日期时间从“transaction”组中选择计数（在“unixepoch”、“localtime”处创建的计数）、日期时间（在“unixepoch”、“localtime”处创建的计数）、本地日期时间（在“unixepoch”、“localtime”处创建的计数），按描述创建的顺序） 列表groupByCreatedAt（）；

结果图像

存储库：
公共列表groupByCreatedAt（）{
返回此.mDataBase.groupByCreatedAt（）；
}

收到错误： 错误：无法确定如何从光标读取此字段

为解决问题而创建的类

Repository:
public List<List<WrapperTransactionModel>>   groupByCreatedAt() {
    return this.mDataBase.groupByCreatedAt();
}

公共类包装器TransactionModel{
@ColumnInfo（name=“发生次数”）
私人名单号码；
@ColumnInfo（name=“local\u datetime”）
私有列表localDatetime；

隐藏访问方法（get和set）

欢迎大家帮忙！

---

谢谢！

文件室可以存储和检索的类型/对象有限。它无法（直接）存储/检索列表，因此文件室说它不知道如何处理提取的数据

文件室可以存储字符串，也可以将字符串检索到字符串列表中

因此，我相信您可能希望WrapperTransactionModel

public class WrapperTransactionModel {

@ColumnInfo(name = "number_of_occurrence")
private List<String> numberOfOccurrence;

@ColumnInfo(name = "local_datetime")
private List<String> localDatetime;

以及：-

class WrapperTransactionModel {
    @ColumnInfo(name = "number_of_occurrence")
    private String numberOfOccurrence;

    @ColumnInfo(name = "local_datetime")
    private String localDatetime;
    ....

---

早上好@Mike T！我最终选择了另一种对我非常有效的方法。不过，非常感谢你的帮助！现在我要睡觉了。

class WrapperTransactionModel {
    @ColumnInfo(name = "number_of_occurrence")
    private String numberOfOccurrence;

    @ColumnInfo(name = "local_datetime")
    private String localDatetime;
    ....

@Query("SELECT COUNT (created_at) 'number_of_occurrence', datetime (created_at, 'unixepoch', 'localtime') 'local_datetime' FROM 'transaction' GROUP BY datetime (created_at, 'unixepoch', 'localtime') ORDER BY created_at DESC ")
List<WrapperTransactionModel> groupByCreatedAt ();

public class MainActivity extends AppCompatActivity {

    TransactionDatabase db;
    AllDao dao;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        db = Room.databaseBuilder(this,TransactionDatabase.class,"transction.db")
                .allowMainThreadQueries()
                .build();
        dao = db.getDao();

        /*
            Add 15 rows of testing data where
                the first row will have a created_at datetime based upon 60 days ago
                the next 3 rows 30 days ago
                and the remaining 11 today
         */
        long second = 1000;
        long near_a_month = 60 * 60 * 24 * 30;
        long adjust = near_a_month * 2;
        for(int i=0; i < 15; i++) {
            if (i > 0 && i < 3) adjust = near_a_month;
            if (i > 3) adjust = 0;
            dao.insertTransaction(new Transaction(String.valueOf((System.currentTimeMillis() / second) - adjust)));
        }

        // Get the data using the Query
        List<WrapperTransactionModel> myTransactionModels = dao.groupByCreatedAt();

        // Write the extracted data out to the log (3 row counts 11,3 and 1 )
        for(WrapperTransactionModel wtm: myTransactionModels) {
            Log.d("WTMINFO","NumberOfOccurrences = " + wtm.getNumberOfOccurrence()+ " LocalDateTime = " +wtm.getLocalDatetime());
        }
    }
}

2021-04-22 19:57:06.738 D/WTMINFO: NumberOfOccurrences = 11 LocalDateTime = 2021-04-22 19:57:06
2021-04-22 19:57:06.739 D/WTMINFO: NumberOfOccurrences = 3 LocalDateTime = 2021-03-23 20:57:06
2021-04-22 19:57:06.739 D/WTMINFO: NumberOfOccurrences = 1 LocalDateTime = 2021-02-21 20:57:06