如何捕获空参数并允许在ADO.NET中使用DBNull进行解析

Question

因此，我将这18个参数传递给DAL，然后插入或更新Access数据库。

我有2个字段，分别是DateTime和一个和int 。 DateTime和int参数均为“非必需”，这意味着可以为空字符串。

当我传递txtBirthDate.Text, txtHireDate.Text, and txtReportsTo.Text ，我遇到了一个问题txtBirthDate.Text, txtHireDate.Text, and txtReportsTo.Text即如果将它们保留为空，则DAL会以FormatException对我txtBirthDate.Text, txtHireDate.Text, and txtReportsTo.Text因为它无法解析null元素。

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Parameters接受它们。 我也不确定如何将这些变量设置为空字符串传递到我的DAL的DBNull.Value 。

这是我的DAL方法调用的示例：

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);

这是我的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;

Answer 1

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;

对其余的字符串值重复此操作