sqlite - 尝试使用ExecuteScalar <object>从表中检索数据时出错？

我有这个课：

public class BtnCountViews
{
    public int btnCount { get; set; }
    public int views { get; set; }
}

我正在尝试从数据库中检索一行数据：

sql = " AVG (BTNACOUNT + BTNBCOUNT) AS btnCount, AVG (VIEWS) As views ";
var avg = db2.ExecuteScalar<BtnCountViews>("SELECT " + sql + " FROM CLICKHISTORY");

但这引发了异常的说法：

System.NotSupportedException: Don't know how to read Japanese.BtnCountViews
at SQLite.SQLiteCommand.ReadCol (SQLitePCL.sqlite3_stmt stmt,

我试图研究ExecuteScalar，看来它可以带一个对象。

有谁知道为什么它会引发异常？

作为参考，下面是CLICKHISTORY表的对象定义：

public class ClickHistory
{
    [PrimaryKey, NotNull]
    public string Yymmdd { get; set; }
    public int DayOfYear { get; set; }
    public int Year { get; set; }
    public int Month { get; set; }
    public int Day { get; set; }
    public int BtnACount { get; set; }
    public int BtnBCount { get; set; }
    public int BtnCCount { get; set; }
    public int BtnDCount { get; set; }
    public int Views { get; set; }
}

最佳答案

您正在尝试返回BtnCountViews类型，而不是标量值。

通过BtnCountViews返回投影的Query：

var sql = "AVG (BTNACOUNT + BTNBCOUNT) AS btnCount, AVG (VIEWS) As views ";
var avg = conn.Query<BtnCountViews>("SELECT " + sql + " FROM CLICKHISTORY").First();

Log.Debug(TAG, $"{avg.btnCount} : {avg.views}");

或通过ExecuteScalar在两个单独的查询中带回标量：

var sql2 = "(AVG (BTNACOUNT + BTNBCOUNT))";
var btnABAvg = conn.ExecuteScalar<int>("SELECT " + sql2 + " FROM CLICKHISTORY");

var sql3 = "(AVG (VIEWS))";
var viewAvg = conn.ExecuteScalar<int>("SELECT " + sql3 + " FROM CLICKHISTORY");

Log.Debug(TAG, $"{btnABAvg} : {viewAvg}");

关于sqlite - 尝试使用ExecuteScalar <object>从表中检索数据时出错？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/47676706/