C# Null Syntax - How To Set A Field To Be Nullable
Feb 6, 2011
I remember being told that you can add some syntax to the end of a statement that will do something if the field is null. Pretty vague, but I cant seem to find anything about it via google.
I definitely isnt how to set a field to be nullable. I know that.
Here is an example of what I want.
int? field1 = 0;
field1 = int.parse(string2); (where string2 is a passed value, that could be null)
I thought there was something you could put at ?? if it is a null, such as:
field1 = int.parse(string2) ??;
Or do I have to check every if every string2 is null before making that statement.
Can anyone reliably get the EDS to save a nullable column to the databse as a "null" when bound to any of the controls such as "FormView"?I have tried using several different UpdateParameters (Session, ControlParamater, Parameter, etc). I have tried setting "ConvertEmptyStringToNull" to true and leaving the property off entirely. Nothing works. On my "Inserts" it works fine.(I have made sure the column is set to nullable = true in the Entity Designer.....)
Got a nullable datetime member on my viewmodel.the moment it hit my controller action, the viewmodel's modelstate allready are invalid (because the member is null).Forgot...how that works? (using MVC2)Basically my viewmodel have a social security number, passport number and passport expiracy date.If the ssn is entered, I want to ignore the two passport related fields, so I made the expiracy date member nullable.
Like all other viewmodels in this app, each model have it's own validation function that will do validation, and in there I add an error that the date is required or not valid (if using passport number). mvc itself should not care about the date at all.I dont want to give the date a default value, because then the date will show when the form loads, and it must be an empty field (unless I already got a date of course.
I have to change the username column in my database to nullable, which means everywhere in my code, I now have to check username.HasValue and change references to username to username.Value. Is there anything I can do to avoid having to change all the references to username to username.Value?
[System.Web.Script.Services.ScriptService] public class Quotes : System.Web.Services.WebService { ebMethod] public void Calculate(int param1, int? param2)
When i click on the page that represents a controller the following error was displayed:-
"The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type"
On this link of code
var articleapproval = articletyperepository.FindAllArticlesRequireMyApproval().ToList(); while the FindAllArticlesRequireMyApproval execute the following LINQ statement :- var articleapproval= articletyperepository.FindAllArticlesRequireMyApproval().ToList();
where this methods calls the following LINQ statement:-
I have a textbox that I use to gather a date. I would like to have the database store a null if this field is left blank by the user when submitting. I am using the following on my aspx page:
I'm trying to bind a nullable bit column, which at the moment is mostly null, but I need to somehow convert the null to a 'false' on runtime because it doesn't bind to a checkbox if it's null. But, I am currently unable to change the default value and update all records accordingly - is there a way to do this in runtime?
I am making a website to store invoices so i can mail them to clients. So i got a table for clients, invoices and one with invoice products/services. When an invoice has no products/services added to them and it returns null i get the error "the null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type."
I just started with linq. Before i always used mysql. Mostly i just had to call data from 1 table so forgive me if my linq query isn't really correct.
Dim invoices = From i In db.invoices _ Group Join p In db.products On i.id Equals p.invoiceId Into invoiceProducts = Group _ Select New With {i.client.naam, i.titel, (From iP In invoiceProducts Select iP.prijs).Sum}
i show the client's name, the title of the invoice and the total amount the clients will need to pay for products and services.
I have a DetailsView on the page and I have made one of the fields a TemplateField. In the EditItemTemplate and InsertItemTemplate I have a DropdownList that is databound to a table in my Sql Server database. I wanted to add an initial value to the DropdownList namely "- select -" .
I set the AppendDataBoundItems property to true and added the initial value as a ListItem.Markup of the DropdownList
This works fine for new input. The problem is however that the database already has records that were entered through a Windows Application and many of these records has a null value in this field and exceptions are thrown when I tried to open these records and the system tried to set the SelectedValue of the DropdownList.After some more searching I found this help
This now solved the problem of opening a record where the value is null in the database, BUT now the RequiredFieldValidator is not validating anymore to make sure that a databound item is selected for this field and not the initial value "- select -". So basically now it is not checking anymore to see if valid input has been entered for the DropDownList and it accepts "- select -" thus it acts as if the field is not a required field anymore.
In short what is required is that I want to make sure that the user enters a valid selection in the DropDownList, but it must also cater for old records that do not have this field entered yet so that those old records can be opened in the DetailsView .Opening Old records (with null in that field):When these old records are opened in the DetailsView the DropDownlist should show "- select -" when the value in the database is null.
Saving records (old or new records):When saving the record in Insert mode or Update mode the RequiredFieldValidator should show that a valid input is not selected if the DropDownList is still on "- select -".
here is my update query syntax.my problem is.if i update only logo1 and logo3 with null logo2 and img null then my query should be update the other record.just dont update null value record but other should be update.but below my query can not update any record.
UPDATE tbitem set itemname= @itemname,note=@note, price=@price,qty=@qty,logo1=@logo1, logo2=@logo2,logo3=@logo3,img=@img where id =@id and @logo1 is null and @logo2 is null and @logo3 is null and @img is null
How can i use a checkbox to represent a boolean bit field in an MVC View? Out of the box, it defaults to a textbox..There is no boolean datatype in SQL Server 2008 so i used a bit datatype. I guess its a custom template but i cant seem to get the syntax right.
n a grid view I have a column named REQUIRED which has a value of either 0 or 1.I added a checkbox templated field to show the above as checked or unchecked instead of0 or 1. I decoded the value Y or N to 1 or 1 in the sqldatasource
When I tried to add the following "Checked='<%# Eval("BOARD") %>' it does not like it and gives an error.How do accomplish the same for the above checkbox field and the exact syntax to be used
I am LINQ querrying against a datatable. However, I am unsuccessfull with catching null values. Here is my code that is giving me the following error.
[Code]....
I am checking to see if minperc is null. However to check that it still is trying to convert the value to double. Cant figure out a way around it. Here is the error: Cannot cast DBNull.Value to type 'System.Double'. Please use a nullable type.
In Microsoft Access Database Form, I have a series of five fields. I would like to set up a field that is equal to the first field unless that field is null or 0. Then I want the field to be equal to the second field unless that field is null or 0, continuing the same way through the five fields. Being a newb, I have no idea how.
here is my code for selectiong some records from db table
string strSql = "select * from mtblNBD where SentTo=@SentTo and InternalStatus Is NULL order by DeadLine desc"; SqlCommand com = new SqlCommand(strSql, con); com.Parameters.Add("@SentTo", SqlDbType.NVarChar, 50).Value = (string)Session["uname"];
here I am using parameters for SenTo field but not for NULL so it is ok... or should I use parameters for this field where value is NULL , if yes then how can I use parameter for this
