更新時從字符串到類型'Double'的轉換無效

Question

我正在嘗試更新表格行。 查詢似乎可以，但是不明白為什么會出現此錯誤

錯誤-

System.InvalidCastException：從字符串“ UPDATE hospitals SET ticketsCount”到類型“ Double”的轉換無效。 ---> System.FormatException：輸入字符串的格式不正確。 在Microsoft.VisualBasic.CompilerServices.Conversions.ParseDouble（String Value，NumberFormatInfo NumberFormat）處-在Microsoft.VisualBasic處內部異常堆棧跟蹤的結尾-在Microsoft.VisualBasic處E：\\ MY WEB \\ Health Saviour \\ website \\中Microsoft.VisualBasic.CompilerServices.Conversions.ToDouble（String Value）的Hospital.details.sendReview_Click（Object sender，EventArgs e）處的.CompilerServices.Conversions.ToDouble（String Value，NumberFormatInfo NumberFormat）網站\\ hospital-details.aspx.vb：第281行

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Dim hospitalID As String = Request.QueryString("hospitalID")
Dim totalScoreFrom As Integer
Dim currentCount As Integer
Dim newAvgRating As Integer
Dim currentScore As Integer
Dim newVotingCount As Integer
Dim votesGiven As Integer
Dim newCurrentScore As Integer

                    currentCount = totalVotes.Text
                    newVotingCount = (Val(currentCount) + 1)
                    totalScoreFrom = newVotingCount * 6 * 10
                    votesGiven = Val(Mrating2) + Val(Mrating3) + Val(Mrating4) + Val(Mrating5) + Val(Mrating6) + Val(Mrating7)
                    newCurrentScore = Val(currentScore) + Val(votesGiven)
                    newAvgRating = newCurrentScore * 10 / totalScoreFrom
                    'formula for avg rating = currentScore * 10 / totalScroreFrom
                    Dim con As New MySqlConnection
                    Dim query As New MySqlCommand
                    con.ConnectionString = ConfigurationManager _
                    .ConnectionStrings("conio").ConnectionString()
                    query.Connection = con
                    query.CommandText = "UPDATE hospitals SET votesCount = '" + newVotingCount + "', currentAvgRating = '" + newAvgRating + "', totalScoreGiven = '" + newCurrentScore + "' WHERE hospitalID = '" + hospitalID + "'"
                    query.Parameters.AddWithValue("@hospitalID", hospitalID)
                    query.Parameters.AddWithValue("@votesCount", newVotingCount)
                    query.Parameters.AddWithValue("@newAvgRating", newAvgRating)
                    query.Parameters.AddWithValue("@newCurrentScore", newCurrentScore)
                    query.ExecuteNonQuery()
                    con.Close()

Answer 1

在給定的代碼段中，您以錯誤的方式使用了參數。 它不會向查詢添加任何參數，使用方式如下：

query.CommandText = "UPDATE hospitals SET votesCount = @votesCount," &_ 
                     currentAvgRating = @currentAvgRating," &_ 
                     totalScoreGiven = @totalScoreGiven" &_
                     newCurrentScore =@newCurrentScore WHERE hospitalID = @hospitalID"   
query.Parameters.AddWithValue("@votesCount", newVotingCount)
query.Parameters.AddWithValue("@currentAvgRating ", currentAvgRating)
query.Parameters.AddWithValue("@totalScoreGiven", newAvgRating)
query.Parameters.AddWithValue("@newCurrentScore", newCurrentScore)
query.Parameters.AddWithValue("@hospitalID", hospitalID)

注意：在這種情況下， Parameters.Add()會更適合，因為您也可以指定參數類型。