c# - 尝试 Convert.ToInt32(value) 时指定的转换无效

Question

我正在尝试运行一个存储过程，由于某种原因它一直告诉我“指定的转换无效”。 “hidSelectedExpenseIDs”是一个隐藏字段，由 id 的 javascript 数组填充。

示例:“hidSelectedExpenseIDs.Value” 看起来像“123,124,125,126”。这就是为什么我有 .Split(',') 在那里。

这是我的代码:

public void hasExhistingExpenseInvoice()
{
    string[] Expenses = hidSelectedExpenseIDs.Value.Split(',');

    //check if there is an existing invoice. Then report back to the user so the
    //user knows if he/she has to check overwrite option.
    bool invoiceExists = false;

    foreach (var expense in Expenses)
    {
        var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["OSCIDConnectionString"].ToString());
        var command = new SqlCommand("p_CaseFiles_Expenses_InvoiceExhists", connection);
        command.Parameters.Add(new SqlParameter("@ExpenseID", SqlDbType.Int));
        command.Parameters["@ExpenseID"].Value = Convert.ToInt32(expense);
        command.CommandType = CommandType.StoredProcedure;
        try
        {
            connection.Open();
            invoiceExists = (bool)command.ExecuteScalar();
            if (invoiceExists)
            {
                //previous invoice exhists
                Warning1.Visible = true;
                Warning1.Text = "There is an exhisting Invoice.";
            }
        }
        catch (SqlException sql)
        {
            lblStatus.Text = "Couldn't connect to the Database - Error";
            lblStatus.ForeColor = System.Drawing.Color.Red;
        }
        catch (Exception ex)//catches exception here
        {
            lblStatus.Text = "An error occured";
            lblStatus.ForeColor = System.Drawing.Color.Red;
        }
        finally
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
        }
    }
}

这是我的存储过程:

ALTER PROCEDURE dbo.[InvoiceExhists]
@ExpenseID int
AS
BEGIN
    SELECT InvNumber FROM dbo.Expenses from ExpID = @ExpenseID
END

Answer 1

逻辑错误。

您的查询返回一个数字，并且您尝试将其直接转换为 bool 值，这在 C# 中无法完成。

某些语言会将任何非零解释为 true，但 C# 并非如此，并且会引发异常。

您需要比较返回的值。

在这种情况下，您应该只检查是否有值，因为如果发票不存在，将返回 NULL。

这看起来像这样:

invoiceExists = command.ExecuteScalar() != null ;

我还建议阅读这篇文章thread并考虑使用 UDF 而不是标量存储过程。