I want to import data from Excel to DataBase using EPPLUS. From here I took code: https://www.paragon-inc.com/resources/blogs-posts/easy_excel_interaction_pt6
The problem is that sometimes in excel are empty Cells. And if cell is empty then I receive an error: NullReferenceException, and my application stops. I think good solution would be assign null value to specific variable if there is no reference e.g. if(LAST_NAME returns NullReferenceException then LAST_NAME = null) - but I don't know how to do this in code.
var newRecord = new DB_USER
{
ID = Int32.Parse(worksheet.Cells[idColumn + row].Value.ToString()),
FIRST_NAME = worksheet.Cells[firstNameColumn + row].Value.ToString(),
LAST_NAME = worksheet.Cells[lastNameColumn + row].Value.ToString() //If this value has NullReferenceException then assign null or ""
};
I thing its fine to assign a empty string i.e. string.Empty for empty cells .And if you are fine you can put it this way :
var newRecord = new DB_USER
{
ID = Int32.Parse(worksheet.Cells[idColumn + row].Value.ToString()),
FIRST_NAME = worksheet.Cells[firstNameColumn + row].Value.ToString(),
LAST_NAME = worksheet.Cells[lastNameColumn + row].Value ?? string.Empty).ToString() //for a null value assign a empty string else the string value
};
A cleaner approach would be Extension method :
public static string ToNullSafeString(this object obj)
{
return (obj ?? string.Empty).ToString();
}
and use it as :
LAST_NAME = worksheet.Cells[lastNameColumn + row].Value.ToNullSafeString();
still if you wish to return a null instead of string.Empty then a slight modification to ToNullSafeString extension method above will work.
If you are using the latest C# version (6.0) then you can use the null propagation operator:
LAST_NAME = worksheet?.Cells[lastNameColumn + row]?.Value?.ToString()
Related
I'm trying to loop through the DataGridView rows and then send the values for an update in my SQL-DB. I can make the update, but the program crashes when I come to the end of the rows, because then it read a null-value.
Exception: System.NullReferenceException, Additional information: Object reference not set to an instance of an object.
I have two questions:
Why can't I stop the method with return (see below) with my if
statement?
How can I let the loop insert null values in the strings? Some of
my columns it's OK to send null-values to. And some not, is there
any way to choose which?
private void editEmployeeDGV()
{
foreach (DataGridViewRow row in employeeDataGridView.Rows)
{
if (row.Cells["SocialSNColumn"].Value.ToString() == null)
{
return;
}
string SocialSN = row.Cells["SocialSNColumn"].Value.ToString();
string Name = row.Cells["nameColumn"].Value.ToString();
string Surname = row.Cells["SurnameColumn"].Value.ToString();
string Email = row.Cells["EmailColumn"].Value.ToString();
string TelNr = row.Cells["TelNrColumn"].Value.ToString();
string Gender = row.Cells["GenderColumn"].Value.ToString();
string ECName = row.Cells["ECNameColumn"].Value.ToString();
string ECNumber = row.Cells["ECNumberColumn"].Value.ToString();
cont.editEmployeeDGV(SocialSN, Name, Surname, Email, TelNr, Gender, ECName, ECNumber);
}
}
The reason for the exception is that you're trying to call the ToString() method on the Value property, but it's null.
if (row.Cells["SocialSNColumn"].Value.ToString() == null)
{
return;
}
There's no reason to cast to a string first; just test for null:
if (row.Cells["SocialSNColumn"].Value == null)
{
return;
}
Your other lines of code run the same risk of throwing an NRE if any of their Value properties are null. To avoid those, you may want to replace ToString() with the Convert.ToString() method, which replaces null with an empty string:
string SocialSN = Convert.ToString(row.Cells["SocialSNColumn"].Value);
string Name = Convert.ToString(row.Cells["nameColumn"].Value);
EDIT:
Thanks to everyone who replied! I appreciate all of your answers :)
So I have a class with the following constructor:
public Transaction(DataRow row)
{
LastName = row.Field<string>("LastName");
FirstName = row.Field<string>("FirstName");
MI = row.ItemArray[3].ToString()[0];
ContactNumber = row.ItemArray[4].ToString();
Hours = int.Parse(row.ItemArray[5].ToString());
CheckIn = (DateTime)row.ItemArray[6];
roomNumber = int.Parse(row.ItemArray[9].ToString());
//Paid = row.Field<int>("Paid");
//TotalBill = row.Field<int>("TotalBill");
}
Notice I have 2 of them commented out with /'s That's because if I don't they return null values even if I try ''row.Field([Whatever]).GetValueOrDefault()'', it still comes out null and my constructor returns null. I also have my DB set with default values so IDK what's wrong.
Anyone got a work around? :)
The DataRow class has a method that is called IsNull and that could receive the column name.
Just combine it with the conditional operator
Paid = row.IsNull("Paid") ? 0 : row.Field<int>("Paid");
the same is true for all other fields that could contain a null value.
Just check for null first and supply a default value:
public Transaction(DataRow row)
{
LastName = row.Field<string>("LastName");
FirstName = row.Field<string>("FirstName");
MI = row.ItemArray[3].ToString()[0];
ContactNumber = row.ItemArray[4].ToString();
Hours = int.Parse(row.ItemArray[5].ToString());
CheckIn = (DateTime)row.ItemArray[6];
roomNumber = int.Parse(row.ItemArray[9].ToString());
Paid = row.Field<int?>("Paid") ?? 0;
TotalBill = row.Field<int?>("TotalBill") ?? 0;
}
See the ?? Operator (C# Reference) page on MSDN for further information on the ?? operator.
You can simply use the Nullable type and GetValueOrDefault method or use null coalescing operator.
Paid = row.Field<int?>("Paid").GetValueOrDefault()
or
Paid = row.Field<int?>("Paid") ?? 0
In both cases Paid will have a value of 0, you can change if you want.
Create your own little function that does a simple check.
Along the lines of:
public integer GetNumber (object val)
{
if (IsNumeric (val))
{
return val;
} else
{
return 0;
}
}
I'm not fantastic with C#, but that should give you an idea. Sorry about formatting, I'm on a phone which doesn't help at all.
I am custom importing some rows from a text file to our database and so I have bunch of codes like this for many fields.
address.State = row["Location State"].ToString();
I just noticed a requirement that says
don't overwrite those fields in the value that we are reading from the
text file is empty or blank.
So I assume I can wrap them all around a check like this?
if(!String.IsNullOrEmpth(row["Location State"].ToString()))
address.State = row["Location State"].ToString();
But before I go ahead and apply this kind of logic around all those fields I wanted to check and see if you have better solutions?
Maybe an extension method could help here:
public static string ColumnValueOrDefault(this DataRow row, string column, string defaultValue)
{
if (row == null)
{
throw new ArgumentNullException("row");
}
if (column == null)
{
throw new ArgumentNullException("column");
}
if (defaultValue == null)
{
throw new ArgumentNullException("defaultValue");
}
var rowString = row[column].ToString();
return string.IsNullOrEmpty(rowString) ? defaultValue : rowString;
}
Address.State = row.ColumnValueOrDefault("column", Address.State);
I would (and do) use this pattern personally :
string sTester = string.Empty
Address.State = string.IsNullOrEmpty(sTester = row["collumn"].ToString()) == false ? sTester : Address.State;
This allows each collumn value to be set once, and the reused using the same string variable, and is relatively readable
I have wrote a c# function in order to parse an XML Stream.
My XML can have several nodes.
Example :
<Stream>
<One>nnn</One>
<Two>iii</Two>
<Three>jjj</Three>
</Stream>
But sometimes, it is :
<Stream>
<Two>iii</Two>
</Stream>
Here is my c# code :
var XML = from item in XElement.Parse(strXMLStream).Descendants("Stream") select item;
string strOne = string.Empty;
string strTwo = string.Empty;
string strThree = string.Empty;
if ((item.Element("One").Value != "")
{
strOne = item.Element("One").Value;
}
if ((item.Element("Two").Value != "")
{
strTwo = item.Element("Two").Value;
}
if ((item.Element("Three").Value != "")
{
strThree = item.Element("Three").Value;
}
With this code, if my Stream is full ( Node On, Two and three), there's no problem! But, if my Stream has only the node "Two", I get a NullReferenceException.
Is there a way to avoid this exception (I cannot change my Stream).
Thanks a lot :)
You should check if item.Element("anything") is null before accessing it's Value property.
if (item.Element("Three") != null && item.Element("Three").Value != "")
You need to do:
if (item.Element("One") != null)
{
strOne = item.Element("One").Value;
}
.Element(String) returns null if an element of the name you requested does not exist.
Checking if value != "" is pointless, because all you are preventing is the reassignment of an empty string to the strOne variable, which is already an empty string. Also, if you really needed to do the empty string check, using String.IsNullOrEmpty(String) method is the preferred way.
Instead of accessing Value property (which raises NullReferenceException if element not exist, as you already know) cast elements to strings. You can use ?? to provide default value for non-existing elements:
string strOne = (string)item.Element("One") ?? String.Empty;
string strTwo = (string)item.Element("Two") ?? String.Empty;
string strThree = (string)item.Element("Three") ?? String.Empty;
Hi guys, probably a simple one.
Using C# .Net 4.0 and Visual Studio 2012 Ultimate.
Got the following code:
string part = "";
part = txtIOpart.Text;
txtBatchCV.Text = txtBatchIO.Text;
txtPartCV.Text = part;
txtExternalCV.Text = Sqlrunclass.SplitSpec_External(part, pg);
txtInternalCV.Text = Sqlrunclass.SplitSpec_Internal();
txtABSCV.Text = Sqlrunclass.SplitSpec_cvABS();
txtOilCV.Text = Sqlrunclass.SplitSpec_OilSeal();
txtBarCV.Text = "*" + Sqlrunclass.SplitInfo_ASno(part, pg) + "*";
txtBarNumCV.Text = txtBarCV.Text;
txtLocnCV.Text = Sqlrunclass.SplitInfo_Location();
txtFitsCV.Text = Sqlrunclass.SplitInfo_Desc();
txtHeightCV.Text = Sqlrunclass.SplitSpec_Height();
txtDiameterCV.Text = Sqlrunclass.SplitSpec_Diameter();
txtCirclitCV.Text = Sqlrunclass.SplitSpec_Circlit();
picTypeCV.Image = ftpclass.Download("CVspecType" + Sqlrunclass.SplitSpec_TypeCV() + ".jpg", "ftp.shaftec.com/Images/TypeJpg", "0095845|shafteccom0", "4ccc7365d4");
if (txtBatchCV.Text == null || txtBatchCV.Text == "")
{
txtBatchCV.Text = "ALL";
}
As you can see at the bottom I'm checking the batch, but I need to check all of the data thats being set by a bunch of methods. Each one will have a different txt output if it sees a null or blank txt. Is there anyway to shorten this code?
Try, txtBatchCV.Text For example
//Just for null
txtBatchCV.Text = (txtBatchCV.Text ?? "ALL").ToString();
//for both null and empty string
txtBatchCV.Text = string.IsNullOrEmpty(txtBatchCV.Text) ? "ALL": txtBatchCV.Text;
You could iterate through all the textboxes
foreach (var txt in form.Controls.OfType<TextBox>())
{
switch(txt.Id){
case "txtBatchCV":
// Do whatever you want for txtBatchCV e.g. check string.IsNullOrEmpy(txt.Text)
break;
}
}
I borrowed the above from here:
How do I loop through all textboxes and make them run corresponding actions from action dictionary?
In response to the comment I got from Tim, I've added a bit more code to explain what you could do. My code example was never meant to be a full solution.
TextBox.Text is never null, it will return "" then. If your methods return null you could use the null-coalescing operator:
string nullRepl = "ALL";
txtExternalCV.Text = Sqlrunclass.SplitSpec_External(part, pg) ?? nullRepl;
txtInternalCV.Text = Sqlrunclass.SplitSpec_Internal() ?? nullRepl;
txtABSCV.Text = Sqlrunclass.SplitSpec_cvABS() ?? nullRepl;
txtOilCV.Text = Sqlrunclass.SplitSpec_OilSeal() ?? nullRepl;
txtLocnCV.Text = Sqlrunclass.SplitInfo_Location() ?? nullRepl;
txtFitsCV.Text = Sqlrunclass.SplitInfo_Desc() ?? nullRepl;
txtHeightCV.Text = Sqlrunclass.SplitSpec_Height() ?? nullRepl;
txtDiameterCV.Text = Sqlrunclass.SplitSpec_Diameter() ?? nullRepl;
txtCirclitCV.Text = Sqlrunclass.SplitSpec_Circlit() ?? nullRepl;
For starters you could use string.IsNullOrEmpty(txtBatchCV.Text), it's a convevience method that basically does what you do in the if check.
You can atleast use one of these methods:
string.IsNullOrEmpty(txtBatchCV.Text)
or
string.IsNullOrWhitespace(txtBatchCV.Text)
I would try something like this:
void SetDefaultIfNull(TextBox txt, string defaultVal)
{
if (string.IsNullOrWhitespace(txt.Text))
txt.Text = defaultVal;
}
Then pass each textbox and the default to the method.