Develop Reference

How to handle null values from SQLite DB with C#?

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.

setting a value based on another value in a linq query

I'm changing a variable from a string a byte in my business logic but I'm not touching the database field that contains the value yet. So in the meantime, I'm looking for a c# equivalent to javascript's conditional syntax SomeValue = (TestValue === Something) ? 1 : 2;
Basically, the linq-to-sql query I have looks like this:
var TheOutput = from x in MyDC.SomeTable
....
select new SomeModel()
{
SomeByte = (x.SomeField === "test") ? 1 : 0
}
SomeField is a string and if it's equal to some test string then I want the property of the output's model to be set to a byte.

Use
(x.SomeField == "test") ? 1 : 0;

Cast to byte explicitly. SomeByte = (byte)(x.SomeField=="test"?1:0) should work.

for example
select new SomeModel()
{
SomeByte = (x.SomeField == "test") ? Convert.ToByte(1); : Convert.ToByte(0);
}

Handling null objects in object setters

I am trying to use a nice near object setter, but have null issues.
My code right now:
var Result = new RefundReplyObject
{
AuthorisationNumber = reply.refundResponse.transactionDetails.authorisationNumber,
ChargeValue = reply.refundResponse.transactionDetails.totalAmount.amount,
Message = reply.refundResponse.transactionDetails.message,
ReconciliationReference = reply.refundResponse.transactionDetails.reconciliationReference,
SettlementDate = reply.refundResponse.transactionDetails.settlementDate,
Status = TransactionStatusToLocalModel(reply.refundResponse.transactionDetails.status),
TransactionReference = reply.refundResponse.transactionDetails.transactionReference
};
BUT ... 'totalAmount' might be null. So, I get errors.
Is there a neat way to handle this, so that if 'totalAmount' is null, then set chargevalue to zero?

How about a ternary operator, that checks to see if total amount is null. If it isn't, then use it's amount, otherwise 0.
ChargeValue = (reply.refundResponse.transactionDetails.totalAmount != null) ? reply.refundResponse.transactionDetails.totalAmount.amount : 0,

You could do, for example:
ChargeValue = reply.refundResponse.transactionDetails.totalAmount != null ? reply.refundResponse.transactionDetails.totalAmount.amount : 0

ternary operator to the rescue!
ChargeValue = totalAmount ? totalAmount.amount : 0;

Something like this?
ChargeValue = (null == reply.refundResponse.transactionDetails.totalAmount)
? 0
: reply.refundResponse.transactionDetails.totalAmount.amount

You're not going to be able to do it on the setter side of things since the exception is occuring before you even get there. You can get what you're after (and clean up your code substantially in the process) by doing something like this:
var trans = reply.refundResponse.transactionDetails;
var Result = new RefundReplyObject
{
AuthorisationNumber = trans.authorisationNumber,
ChargeValue = trans.totalAmount == null ? 0 : trans.totalAmount.amount,
Message = trans.message,
ReconciliationReference = trans.reconciliationReference,
SettlementDate = trans.settlementDate,
Status = TransactionStatusToLocalModeltrans.status),
TransactionReference = trans.transactionReference
};

Logic to check for Null Value in Multiple Textboxes

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.

Linq XML query with nested loop - 1

In this question, if I need to get "date" included in the output, what changes should be made?
When I included
let dt = l.Element("Date").Value
It gives, "Object reference not set to an instance of an object"
var query = from l in doc.Descendants("L1")
let dt = l.Element("Date").Value
let id = l.Attribute("id").Value
from subject in l.Descendants("Subject")
select new
{
Date = dt,
Id = id,
SubjectName = (string)subject.Attribute("SubjectName"),
Score = (string)subject.Attribute("Score")
};
foreach (var result in query)
{
Console.WriteLine(result);
}

If l doesn't have an Date element, trying to access l.Element("Date").Value will incur an error. You can use a conditional:
var query = from l in doc.Descendants("L1")
let dt = l.Elements("date").Any()
? l.Element("date").Value
: AnyDefaultValueIWantForDate
let id = l.Attribute("id").Value
from subject in l.Descendants("Subject")
select new
{
Date = dt,
Id = id,
SubjectName = subject.Attribute("SubjectName").Value,
Score = subject.Attribute("Score").Value
};
(I also added the .Value in SubjectName and Score).

Looking at your other XML, it does not, as Mr. Skeet mentioned, have anything in the <date> elements. You will need to explicitly handle that if you aren't planning on always having data in there.
You can do something like this:
let dt = l.Element("date") == null ? string.Empty : l.Element("date").Value

Assuming l is not null then l.Element("Date") is null which would mean that one or more of your L1 elements does not have a child Date element.
The fix would depend on what you want to do with missing dates. If you want to use default(DateTime) as a "magic" date, you could do:
let dt = (l.Element("Date") == null ? default(DateTime) : l.Element("Date").Value)