dbnull

问题 Quite new to C# I need to cast a value to add minutes to a date but it can be null. Here's how I do : if(Eval("DUREE") != DBNull.Value) { var duration = Convert.ToInt32(Eval("DUREE")); var date = Convert.ToDateTime(Eval("DATE")); var dateAsString = Convert.ToString(date.AddMinutes(duration)); DataBinder.Eval(Container.DataItem, dateAsString, "{0:HH:mm}") } else { " - " } Here the error I get : DataBinding : 'System.Data.DataRowView' doesn't comport properties called : '17/04/2014 13:30:00'.

问题 I am trying to initialize an object with data from database return in a dataset as below: Class Pdf Public FileId As Integer Public AccountNumber As Integer Public DateSaved As DateTime Public FileName As String Public DateImported As DateTime Scenerio 1 I can intialize the object like this: Dim pdf = New Pdf With {.FileId = ds.Tables(0).Rows(i)("fileid"), .AccountNumber = ds.Tables(0).Rows(i)("accountnumber"), .DateSaved = ds.Tables(0).Rows(i)("datesaved"), .FileName = ds.Tables(0).Rows(i)(

问题 I have the following LINQ query which always results in an error when my "Remark" column in dtblDetail is null, even though I test if it is NULL. var varActiveAndUsedElementsWithDetails = from e in dtblElements join d in dtblDetails on e.PK equals d.FK into set from d in set.DefaultIfEmpty() where (e.ElementActive == true) select new { ElementPK = e.PK, Remark = d.IsRemarkNull() ? null : d.Remark }; The error message was: "The value for column 'Remark' in table 'dtblDetails' is DBNull." After

问题 I get this exception when I try to insert a DBNull.Value into a nullable varbinary(max) field: Implicit conversion from data type nvarchar to varbinary(max) is not allowed. Use the CONVERT function to run this query. Thats my code: insertCMD.Parameters.AddWithValue("@ErrorScreenshot", SqlDbType.VarBinary).Value = DBNull.Value; I know there exist duplicate questions on SO, but I do NOT use any String like the others do. What do I wrong? UPDATE: using (var insertCMD = new SqlCommand("INSERT

问题 So, I have a function which reads the result of a query that is used later on the program as it follows: connection.Open(); int combination; using (SqlCommand com1 = new SqlCommand()) { com1.Connection = connection; com1.CommandText = "select FinalComboId from relationTable where sourceCombo=@source and destinationCombo=@destination"; com1.Parameters.Add(new SqlParameter("@source",combo.ToString() ?? "")); com1.Parameters.Add(new SqlParameter("@destination", destination ?? "")); SqlDataReader

问题 How to create a list for a ComboBox that allows DBNull? I tried int? But int? is not the same as DBNull and the combobox does not work with the null value. My datagridview combobox, needs DBNull . I did: var machineComboList = this.eMDataSet1.Machines.Select(row => new { Key = (int?) row.MachineID, Value = row.Description }).ToList(); int? nullValue = DBNull.Value; machineComboList.Add(new { Key = nullValue, Value = "All" }); I want to put a DBNull value into "Key". Using int? does not work.

问题 I guess it is too late and I'm too tired to see what I'm doing wrong. Here is what I'm trying: int imageId = imageDal.AddImage(new SqlParameter[] { new SqlParameter("@IMAGE_ID", SqlDbType.Int, Int32.MaxValue, ParameterDirection.Output, true, 0, 0,"IMAGE_ID", DataRowVersion.Current,DBNull.Value), new SqlParameter("@IMAGE", SqlDbType.Image, 11, ParameterDirection.Input, true, 0, 0,"IMAGE", DataRowVersion.Current,image) }); public int AddImage(SqlParameter[] spParams) { SqlHelper.ExecuteNonQuery

问题 Is there a way to find out which columns are nullable in a DataTable? I know that there is a proprety: DataColumn.AllowDBNull, which can be set to true or false in the design mode of the DataSet, but I would like to have this information directly from the database. I am having a DGV populated with values from a MySQL database and have bound the DataSource of the DGV to a DataTable. 回答1: As a solution I decided to retrieve the Columns Schema of the Database and from there assign which Collumns

问题 IBM Informix SDK: Statement: Update mytable set myblobcolumn = ? where myid = 1; using (IfxConnection conn = GetIfxConnection()) using (IfxCommand cmd = new IfxCommand(updateSql, conn)) { var param = new IfxParameter("myblobcolumn", IfxType.Blob) { IsNullable = true }; cmd.Parameters.Add(param).Value = DBNull.Value cmd.ExecuteNonQuery(); //ERROR [HY000] [Informix .NET provider][Informix]Illegal attempt to use Text/Byte host variable. } If I update it with another IfxBlob object it works fine,

问题 The stored procedure for command can return null.Is it correct way to check if the returned value is null or should I also check that obj is null? object obj = command.ExecuteScalar(); int id = -1; if (DBNull.Value == obj) { id = Convert.ToInt32(obj ); } 回答1: You probably want to change your if-statement to if (obj != null && DBNull.Value != obj) { ... } Right now you're trying to convert if obj == DBNull.Value . 回答2: If there is no result your query can return null , so in the general case