C# 如何在ADO.NET中捕获null参数并允许使用DBNull进行解析

因此，我将这18个参数传递给我的DAL，然后插入或更新我的Access数据库

我有两个字段，分别是

DateTime

和

int

。DateTime和int参数都是“notrequired”，这意味着可以是空字符串

当我将

txtbirchdate.Text、txtHireDate.Text和txtrepto.Text传递给我时，我遇到了一个问题，如果它们被保留为null，我的DAL会向我发出一个
FormatException
，无法通过对null元素的解析

所以我现在的问题是，我不确定在哪里解析
DateTime
和
int
变量以允许我的参数接受它们。我还不确定如何将这些变量设置为
DBNull.Value
，这些变量已作为空字符串传递给我的DAL

以下是我的DAL方法调用示例：

rowsAdded = ((DataAccessLayer)Application["dbAccess"]).insertEmployees(txtLname.Text, txtFname.Text, txtTitle.Text, 
         txtCourt.Text,txtBday.Text,txtHireDate.Text, txtAddress.Text, txtCity.Text,txtRegion.Text,txtPostalCode.Text,
         txtCountry.Text, txtHomePhone.Text, txtExtension.Text, upPhoto.FileName.ToString(),txtNotes.Text,txtReports.Text,txtPassword.Text);

以下是我的DAL方法：

 public int insertEmployees(string lname, string fname, string title, string toc, string birth, string hire, string address, string city,
    string region,string postal,string country, string phone, string ext,string photo, string notes, string report, string pass)
{
    string last = lname;
    string first = fname;
    string tlt = title;
    string tOfc = toc;
    string addy = address;
    string town = city;
    string reg = country;
    string phum = phone;
    string exten = ext;
    string rep = report;// THIS IS Int
    string pas = pass;
    string pc = postal;
    string note = notes;
    string regions = region;
    string hD = hire;// THIS IS DATETIME
    string bD = birth;// THIS IS DATETIME
    string pho = photo;
    int rows = 0;
        dbString = "INSERT INTO [Employees] ([LastName],[FirstName],[Title],[TitleOfCourtesy],[BirthDate],[HireDate],[Address],[City],[Region],[PostalCode]," +
        "[Country],[HomePhone],[Extension],[Photo],[Notes],[ReportsTo],[Password]) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)";
        string queryLast = "Select @@Identity";

        conn.Open();
        oleCommand = new OleDbCommand(dbString, conn);

        oleCommand.Parameters.Add(new OleDbParameter("@LastName", OleDbType.VarChar, 20, ParameterDirection.Input, false, 10, 0, "LastName", DataRowVersion.Original, null)).Value = last;
        oleCommand.Parameters.Add(new OleDbParameter("@FirstName", OleDbType.VarChar, 10, ParameterDirection.Input, false, 10, 0, "FirstName", DataRowVersion.Original, null)).Value = first;
        oleCommand.Parameters.Add(new OleDbParameter("@Title", OleDbType.VarChar, 30, ParameterDirection.Input, true, 10, 0, "Title", DataRowVersion.Original, null)).Value = tlt ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@TitleOfCourtesy", OleDbType.VarChar, 25, ParameterDirection.Input, true, 10, 0, "TitleOfCourtesy", DataRowVersion.Original, null)).Value = tOfc ?? (object)DBNull.Value;
//DATE  oleCommand.Parameters.Add(new OleDbParameter("@BirthDate", OleDbType.DBDate, 20, ParameterDirection.Input, true, 10, 0, "BirthDate", DataRowVersion.Original, null)).Value = (object)bD ?? DBNull.Value;
//DATE  oleCommand.Parameters.Add(new OleDbParameter("@HireDate", OleDbType.DBDate, 20, ParameterDirection.Input, true, 10, 0, "HireDate", DataRowVersion.Original, null)).Value = (object)hD ?? DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Address", OleDbType.VarChar, 60, ParameterDirection.Input, true, 10, 0, "Address", DataRowVersion.Original, null)).Value = addy ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@City", OleDbType.VarChar, 15, ParameterDirection.Input, true, 10, 10, "City", DataRowVersion.Original, null)).Value = phum ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Region", OleDbType.VarChar, 15, ParameterDirection.Input, true, 10, 0, "Region", DataRowVersion.Original, null)).Value = regions ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@PostalCode", OleDbType.VarChar, 10, ParameterDirection.Input, true, 10, 0, "PostalCode", DataRowVersion.Original, null)).Value = pc ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Country", OleDbType.VarChar, 15, ParameterDirection.Input, true, 10, 0, "Country", DataRowVersion.Original, null)).Value = reg ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@HomePhone", OleDbType.VarChar, 24, ParameterDirection.Input, true, 10, 0, "HomePhone", DataRowVersion.Original, null)).Value = phum ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Extension", OleDbType.VarChar, 4, ParameterDirection.Input, true, 10, 0, "Extension", DataRowVersion.Original, null)).Value = exten ?? (object)DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Photo", OleDbType.VarChar, 255, ParameterDirection.Input, true, 10, 0, "Photo", DataRowVersion.Original, null)).Value = pho ?? (object)DBNull.Value; ;
        oleCommand.Parameters.Add(new OleDbParameter("@Notes", OleDbType.VarWChar, 255, ParameterDirection.Input, true, 10, 0, "Notes", DataRowVersion.Original, null)).Value = note ?? (object)DBNull.Value;
  //INT oleCommand.Parameters.Add(new OleDbParameter("@ReportsTo", OleDbType.Integer, 2, ParameterDirection.Input, true, 10, 0, "ReportsTo", DataRowVersion.Original, null)).Value = (object)rep ?? DBNull.Value;
        oleCommand.Parameters.Add(new OleDbParameter("@Password", OleDbType.VarChar, 255, ParameterDirection.Input, false, 10, 0, "Password", DataRowVersion.Original, null)).Value = pas ?? (object)DBNull.Value;
        rows = (int)oleCommand.ExecuteNonQuery();
        oleCommand.CommandText = queryLast;

对于字符串值，可以使用以下表达式：

oleCommand.Parameters.Add(new OleDbParameter("@LastName", OleDbType.VarChar, 20, 
                                             ParameterDirection.Input, false, 10, 
                                             0, "LastName", 
                                             DataRowVersion.Original, null)
                         ).Value = String.IsNullOrEmpty(last) ? DBNull.Value : last;

对其余字符串值重复此操作
我已编辑了您的标题。请参阅“”，其中的共识是“不，他们不应该”。可能重复