Assign DBNull.Value To A Variable, Or Write NULL To MSSQL Database?
Dec 3, 2009
I have a little problem regarding the use of DBNull, NULL etc. in VB.net in combination with SQL Server 2k.
More specifically, I want to do something along the lines of this:If x = 0 Then
x = DBNull.Value where x is declared by Dim x as Object. I would rather use Double, but I can't assign DBNull.Value to this, and using Object works quite well, too. But every time I hit this condition, I get an exception: A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll This is not a major show-stopper, since the database value I write x to in the next step, is NULL by default - most of the time! So I need the ability to write NULL to it. If that was not the case, I would have been able to work around this by catching exceptions, I think - but sadly, this isn't really of use then.
I am not sure why VB makes everything such a pain. I have a fields which stores the date and time in the format required to store in MySQL database
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Now I need to assign the AppDate to NUll like DBNull, but I am not able to do it directly. If I change AppDate to Date then I am not getting the required format.
How can I change the following code to write to the database null instead of empty strings?
Public Sub SetChangeRequest(ByVal referenceLeaseID As Integer, _ ByVal referenceCustomerID As Integer, _ Optional ByVal custUnitNum As Object = Nothing, _
am trying to write to a database via a stored procedure. I am trying to save my values to an object and then write to the database. When I click the button to save the record I am getting a null reference.The below is from the frmDMR class.
Public Class frmDMR Private m_dmrissue As DMRData Public Property NewDmrIssue() As DMRData
A stored procedure returns data about a user record including a nullable datetime column for their last login date. Which one is the better choice in dealing with the possibility for NULL values when trying to assign a .Net date variable?
Try _LastLogin = CDate(DT.Rows(0)("LastLogin")) Catch ex As InvalidCastException
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Which is the preferred method of handling possible NULL values from the database? Is there a better way than the three listed?
Edit #2: I have noticed that the TryParse method does not play nice when trying to assign to a Nullable type.
I need to write a String Array to a field in a MSSQL Database, however, I'm not sure how to do the connection from javascript to the backend VB.NET to send the data to the DB. Do I need to create a web service and use ajax/json?
Pulling a record from the DB and populating a list view but keep getting conversion from DBNull to Single is invalid (words to that effect). The code is below with bold highlighting where problem is and a bit more helpful description of error. I get this error: "Conversion from type 'DBNull' to type 'Single' is not valid." [Code]
I tried DbNull.Value but no luck. How do I assign a default value as null to a string parameter that is null in VB.NET? Its litte strange to see that VB does not have anything like plain null as most of the other languages do. Also what is the difference between null and DbNull and Nothing.
I use VB .NET 2002 (academic version) I have created an MS Access database to be populated with vaules extracted from dBase files. Some numerical values can be null - ie where no data was recorded in the dBase file. Relevant field properties in MS Access mdb table are set to "Not Required" as follows - dt0 is the name in code of the Access table "AllData":
With dt0.Columns .Append("Date", DataTypeEnum.adDate)
colTest.Name = "Ch1Deg"
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Using an INSERT INTO command I can send a null value to the field:
My problem is how to pass a variable which sometimes takes the value System.DBNull.
If I use SQLMdb = "INSERT INTO [AllData]" " ([Date],[Ch1Deg])" & _ " VALUES ('" & dDate1 & "','" & dDeg & "')
Then when dDeg is numeric then there is no problem and the table is populated. When data is missing and dDeg takes the value System.DBNull then it's a no go! The error message is "Data type mismatch in criteria expression."
Is there a way round this with VB .NET 2002 or do I need to upgrade to a later version which has nullable data types, eg nullable integers and doubles etc?
If you assign a value to a nullable integer via a ternary operator, it can't become null..While this question may seem like a duplicate of many, it is actually being asked for a specific reason.Take this code, for example: Dim n As Integer? = If(True, Nothing, 1) In that code, the ternary expression should be returning Nothing, but it's setting n to 0. If this were C#, I could say default(int?) and it would work perfectly. Now it looks like I am going to have to ditch the ternary and use a regular If block, but I really want to use the ternary. If Nothing were truly VB.NET's equivalent to C#'s default, how can you explain this behavior?
when i try to assign data to an array from a text box, i get a null reference exception, stating "Object reference not set to an instance of an object".
Now I can't use cmbReplcmnt.Text because what I actually need is the value of that SelectedItem
So problem is, if the user leaves the combobox as blank, it throws a null exception.I decided to use the IIf function then:classEquipmentItem.ReplacementTo = IIf(IsNothing(cmbReplcmnt.SelectedItem.ToString), classEquipmentItem.ReplacementTo = "", cmbReplcmnt.SelectedItem.ToString)
Unfortunately I still get the error I tried using a Try-Catch for it and it worked, but I don't want to rely on the Try-Catch, so I was wondering is there a another way to work this through?
I need to save pictures in my database, my database is MSSQL as of now, my code for getting the picture is this:
Private Sub browsepic_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles browsepic.Click With dialogpic 'Open File Dialog sa toolbox .InitialDirectory = "C:UsersCAMILLEPictures"
I am trying to Insert/Delete records in a MSSQL database based on if a checkbox is checked or unchecked. The checkbox is an item template in a datagrid, I can check/uncheck the checkbox but it doesn't do an insert or delete. Here is my code:
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But then I get the error that the control chkmap has not been declared. I am confused as to how this needs to be declared, do I set a variable to the FindControl("chkmap") and then set it as variable.checked = true ?
I was creating an enrollment system for my Thesis, and my adviser told me that I must have a Code in my program that Synchronize database from client and server so that if the terminal connection is "Up" the data will go to the server and if the connection is "Down" the data will go to the installed server on the the local machine. and every 20 mins or 30 mins will sync the database.
I have a question on a datagrid object in vb.net 2008, that I what to be populated with certain values of a parameter from mssql database. The connection is made, the column header are loaded, but I what, when the form is loaded, to populate the datagrid only with certain values, doing a select commnad where id has a value given by me.What is the command to have this select done and display the values in the datagrid?
After a save, if the program crashes before I close the window I am loosing my changes. Is there a way to commit? here is my saving
vb Private Sub TicketBindingNavigatorSaveItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TicketBindingNavigatorSaveItem.Click Me.Validate()
I've been making this BlackJack program for a school project
I have 52 image files, labelled from '_1' to '_52' in my resources folder, each number corresponds to a card.
My question is, how do I get a picture box to assign the correct resource according to a variable
So, say I have
"pictDealerCard1" -> picture box which displays the first of the dealers card DealerCard1 = 37 -> random number generated through INT(RND() * 52) and resource '_37'
I need to assign a varible in a while clause. I.e., i would do it in php like this: while (!is_bool($char=$this->getChar()) in every loop, the function would assign $char a value, the is_bool function would test it, and the code INSIDE the while clause would have access to that $char.
i would like to assign the value of a combobox to a variable and use this variable as a parameter on the insert statement.see code below,code 1 works ok,but code 2 brings an error relating to wrong datatype,i cant seem to find where the problem because i think i am doing everything right.
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i would like code 2 to work so that i can assign the variables different values at different scenarios. column serialno is a foreign key from table Stock.
I want to assign a string value to a variable in the DataGridView LostFocus event. I found that I can't just do variable = "string value, it will give me the "Unable to cast object of type 'system.eventargs' to type 'system.windows.forms.datagridviewcelleventargs'" error.
The function created by double-clicking on the datagridview is:
Private Sub DataGridViewInvoice_LostFocus(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridViewInvoice.LostFocus
