Object cannot be cast from DBNull to other types

Question

Object cannot be cast from DBNull to other types.

I have a following function which throws the above error. I am handling all nulls in store procedure and in the C# code.

So where is it getting this error?

I can see the error in the catch block. But i am not understanding which line in the following create() getting the error.

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;
    }
}

Solution 1

I'm thinking that your output parameter is coming back with a DBNull value. Add a check for that like this

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

Solution 2

I suspect that the line

DataTO.Id = Convert.ToInt64(dataAccCom.GetParameterValue(IDbCmd, "op_Id"));

is causing the problem. Is it possible that the op_Id value is being set to null by the stored procedure?

To Guard against it use the Convert.IsDBNull method. For example:

if (!Convert.IsDBNull(dataAccCom.GetParameterValue(IDbCmd, "op_Id"))
{
 DataTO.Id = Convert.ToInt64(dataAccCom.GetParameterValue(IDbCmd, "op_Id"));
}
else 
{
 DataTO.Id = ...some default value or perform some error case management
}

Solution 3

You need to check for DBNull, not null. Additionally, two of your three ReplaceNull methods don't make sense. double and DateTime are non-nullable, so checking them for null will always be false...

Solution 4

TryParse is usually the most elegant way to handle this type of thing:

long temp = 0;
if (Int64.TryParse(dataAccCom.GetParameterValue(IDbCmd, "op_Id").ToString(), out temp))
{
   DataTO.Id = temp;
}     

Solution 5

Reason for the error: In an object-oriented programming language, null means the absence of a reference to an object. DBNull represents an uninitialized variant or nonexistent database column. Source:MSDN

Actual Code which I faced error:

Before changed the code:

    if( ds.Tables[0].Rows[0][0] == null ) //   Which is not working

     {
            seqno  = 1; 
      }
    else
    {
          seqno = Convert.ToInt16(ds.Tables[0].Rows[0][0]) + 1;
     }

After changed the code:

   if( ds.Tables[0].Rows[0][0] == DBNull.Value ) //which is working properly
        {
                    seqno  = 1; 
         }
            else
            {
                  seqno = Convert.ToInt16(ds.Tables[0].Rows[0][0]) + 1;
             }

Conclusion: when the database value return the null value, we recommend to use the DBNull class instead of just specifying as a null like in C# language.

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Comments

[abatishchev]

Maybe better Convert.IsDBNull()?

[Alexander]

I have multiple integer values in my query. Can I somehow shorten the process or I have to do this for everyone?

[computercarguy]

@Alexander, I hope you found an answer before now, but it can get pretty ugly to get shorter than this, but using s ternary would work: DataTO.Id = dataAccCom.GetParameterValue(IDbCmd, "op_Id") == DBNull.Value ? null : Convert.ToInt64(dataAccCom.GetParameterValue(IDbCmd, "op_Id"));