c# - 对象不能从 DBNull 转换为其他类型

Question

对象不能从 DBNull 转换为其他类型。

我有一个抛出上述错误的函数。我正在处理存储过程和 C# 代码中的所有空值。

那么它是从哪里得到这个错误的呢？

我可以在 catch block 中看到错误。但我不明白以下 create() 中的哪一行出现错误。

public Boolean Create(DataTO DataTO)
{
    IDbTrans transaction = null;
    IDbCmd IDbCmd;

    string EncryptedPassword = Encrypt(DataTO.txtPwd);
    Base dataAccCom = null;

    try
    {
        dataAccCom = Factory.Create();
        dataAccCom.OpenConnection();
        transaction = dataAccCom.BeginTransaction();
        IDbCmd = dataAccCom.CreateCommand("sp_Register", true);
        dataAccCom.AddParameter(IDbCmd, "op_Id", DbType.Int64, 0, ParameterDirection.Output);
        dataAccCom.AddParameter(IDbCmd, "p_dlstTitle", DbType.String, ReplaceNull(DataTO.dlstTitle));
        dataAccCom.AddParameter(IDbCmd, "p_txtFirstName", DbType.String, ReplaceNull(DataTO.txtFirstName));
        dataAccCom.AddParameter(IDbCmd, "p_txtMiddleName", DbType.String, ReplaceNull(DataTO.txtMiddleName));
        dataAccCom.AddParameter(IDbCmd, "p_txtLastName", DbType.String, ReplaceNull(DataTO.txtLastName));
        dataAccCom.AddParameter(IDbCmd, "p_txtDob", DbType.DateTime, DataTO.txtDob);
        dataAccCom.AddParameter(IDbCmd, "p_txtDesig", DbType.String, ReplaceNull(DataTO.txtDesig));
        dataAccCom.AddParameter(IDbCmd, "p_txtOFlatNo", DbType.String, ReplaceNull(DataTO.txtOFlatNo));
        dataAccCom.AddParameter(IDbCmd, "p_txtOBuild", DbType.String, ReplaceNull(DataTO.txtOBuild));
        dataAccCom.AddParameter(IDbCmd, "p_txtOPost", DbType.String, ReplaceNull(DataTO.txtOPost));
        dataAccCom.AddParameter(IDbCmd, "p_txtOArea", DbType.String, ReplaceNull(DataTO.txtOArea));
        dataAccCom.AddParameter(IDbCmd, "p_txtOCity", DbType.String, ReplaceNull(DataTO.txtOCity));
        dataAccCom.AddParameter(IDbCmd, "p_txtRBuild", DbType.String, ReplaceNull(DataTO.txtRBuild));
        dataAccCom.AddParameter(IDbCmd, "p_txtRPost", DbType.String, ReplaceNull(DataTO.txtRPost));
        dataAccCom.AddParameter(IDbCmd, "p_txtUserID", DbType.String,ReplaceNull(DataTO.txtUserID));
        dataAccCom.AddParameter(IDbCmd, "p_txtPwd", DbType.String, ReplaceNull(EncryptedPassword));
        dataAccCom.ExecuteNonQuery(IDbCmd);
        DataTO.Id = Convert.ToInt64(dataAccCom.GetParameterValue(IDbCmd, "op_Id"));
        transaction.Commit();
        return true;



    }
    catch (System.Exception ex)
    {
        if (transaction != null)
        {
            transaction.Rollback();
        }
        throw ex;
    }
    finally
    {
        transaction = null;
        if (dataAccCom != null)
        {
            dataAccCom.CloseConnection();
        }
        dataAccCom = null;
        IDbCmd = null;
    }
}

public string ReplaceNull(string value)
{
    if (value == null)
    {
        return "";
    }
    else
    {
        return value;
    }
}

public DateTime ReplaceNull(DateTime value)
{
    if (value == null)
    {
        return DateTime.Now;
    }
    else
    {
        return value;
    }
}

public double ReplaceNull(double value)
{
    if (value == null)
    {
        return 0.0;
    }
    else
    {
        return value;
    }
}

Answer 1

我认为您的输出参数返回的是 DBNull 值。像这样添加一个支票

var outputParam = dataAccCom.GetParameterValue(IDbCmd, "op_Id");
if(!(outputParam is DBNull))
     DataTO.Id = Convert.ToInt64(outputParam);