c# - 无效的转换日期时间？

Question

我有一个包含以下代码的类

 public cCase(string pCaseNo, string pMode)
    {
        if (pMode == "new")
        {
            this._caseNo = Validate_CaseNo(pCaseNo);
        }
        if (pMode == "existing")
        {
            try
            {
                int intValidatedCaseNo = Validate_CaseNo(pCaseNo);
                string sqlText = "SELECT * FROM tblCases WHERE CaseNo = @CaseNo;";
                string strConnection = cConnectionString.BuildConnectionString();
                SqlConnection linkToDB = new SqlConnection(strConnection);
                linkToDB.Open();
                SqlCommand sqlCom = new SqlCommand(sqlText, linkToDB);
                sqlCom.Parameters.Add("@CaseNo", SqlDbType.Int);
                sqlCom.Parameters["@CaseNo"].Value = intValidatedCaseNo;
                SqlDataReader caseReader = sqlCom.ExecuteReader();
                if (caseReader.HasRows)
                    while (caseReader.Read())
                    {
                        this._claimant = caseReader["Claimant"].ToString();
                        this._defendant = caseReader["Defendant"].ToString();
                        this._caseType = caseReader["CaseType"].ToString();
                        this._occupation = caseReader["Occupation"].ToString();
                        this._doa = (DateTime?)caseReader["DOA"];
                        this._dateClosed = (DateTime?)caseReader["DateClosed"];
                        this._dateSettled = (DateTime?)caseReader["DateSettled"];
                        this._dateInstructed = (DateTime?)caseReader["DateInstructed"];
                        this._status = caseReader["Status"].ToString();
                        this._instructionType = caseReader["InstructionType"].ToString();
                        this._feeEstimate = (decimal?)caseReader["FeeEstimate"];
                        this._amountClaimed = (decimal?)caseReader["AmountClaimed"];
                        this._amountSettled = (decimal?)caseReader["AmountSettled"];
                        this._caseManager = caseReader["CaseManager"].ToString();
                    }
                caseReader.Close();
                linkToDB.Close();
                linkToDB.Dispose();
            }
            catch (Exception eX)
            {
                throw new Exception("Error finding case" + Environment.NewLine + eX.Message);
            }
        }
    }

但是日期时间？转换失败并显示“无效转换”。我检查了 SQL 数据库，该字段存储有效日期所以我无法弄清楚为什么，当我通过 DataReader 将信息提取到我的应用程序中时，日期时间字段导致无效转换。

请帮忙。

Answer 1

您将要更改以下行:

this._doa = (DateTime?)caseReader["DOA"];

到:

if (caseReader["DOA"] != DBNull.Value)
    this._doa.Value = (DateTime)caseReader["DOA"];

以及所有类似的行。

DBNull 值不能从 Nullable 类型转换。