Setting A DataSet Row Value To Nothing Initialize It To The Data Type Minvalue?
Dec 2, 2010
When setting a DataSet row column to Nothing, like row.Date = Nothing, why does it initialize it to the data type minvalue? In this case a date, that gets set to 0000-01-01. The column is set to allow null etc., and if I don't set the row to anything at all, it will leave the column empty. So why does Nothing act this way?
In C# I would've set it to DbNull, I guess, but I'm a tad green on VB.NET - as you might be able to tell. :)
i am trying to copy data from a standard Dataset to a Type Dataset (XSD) of same table structure. i want to use Automapper to do that one. So how can i do that using automapper?
How you set data type to string? I am using this source: Dim Resp As String = AxInet1.OpenURL("[URL]", vbNullString) TextBox1.Text = Resp I need to replace the vbnullstring. On other forums, people are saying to use icstring but still i am getting an error that it is not declared and I added reference to imports system.text.
Errors: A first chance exception of type 'System.Runtime.InteropServices.COMException' occurred in AxInterop.InetCtlsObjects.dll A first chance exception of type 'System.ArgumentException' occurred in AxInterop.InetCtlsObjects.dll
i am getting the xml using readxml method. And then display the data in datagrid. But number type columns comes as string type in the dataset. So when datagrid displays , sortingdatagrid columns is not correct. For example it sorts like this:
I need to read data from an Excel sheet as part of a data conversion. Certain columns contain mostly numeric data but may contain some alphanumeric data somewhere in the excel sheet. The problem is, my conversion sees the alphanumeric values as null (or blank. Using the .ToString() method returns ""). To connect to Excel, I'm creating an oledb connection, creating an OleDbDataAdapter, then filling a DataSet with the adapter.
Here's the VB code for connecting: private _oleadpt As OleDbDataAdapter private _oleconnection As New OleDbConnection Dim olecomm As OleDbCommand '_database comes from a settings file and is the full path to an excel document Dim connstring As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" & _database & "; Extended Properties=""Excel 8.0;HDR=YES;""" [Code] .....
I think the data adapter is determining the datatype for the columns based on the first however-many rows it looks at. It decides the columns with numbers are numeric which is the start of my problem. Changing the formatting of the column in Excel doesn't seem to affect the datatypes in my data set. Is there a way to tell the dataadapter or dataset what type of data to use for a column? Or should I try to cast the data in my SQL statement?
VB Private Sub ExportDatasetToCsv(ByVal MyDataSet As DataSet) Dim str As New StringBuilder For Each dr As DataRow In MyDataSet
[code]....
I am getting an error on this line: For Each dr As DataRow In MyDataSet The error is Expression is of type 'System.Data.DataSet', which is not a collection type.
I am building a code behind page that has a public property (MyDTOItem) which is essentially a DTO object (dtDTOItem) Note: In my code the Get and Set are actually real code (I stripped it for the example).The problem I am having is in the Page_Load event. When I set the .Member1 property of the DTO object the Get code runs and not the Set and therefore the DTO ibject property .Member1 never gets assigned. I figured out that if I add code (MyDTOItem = New dtDTOItem) to the Page_Load event then it will set the value correctly. What I am trying to figure out is how to initialize the property object without having to do it explicitly. It has to be an extended property because I have custom Get and Set code.
Public Property MyDTOItem As dtDTOItem Get End Get Set(value As dtDTOItem)
I am building a code behind page that has a public property (MyDTOItem) which is essentially a DTO object (dtDTOItem) Note: In my code the Get and Set are actually real code (I stripped it for the example).
The problem I am having is in the Page_Load event. When I set the .Member1 property of the DTO object the Get code runs and not the Set and therefore the DTO ibject property .Member1 never gets assigned.
I figured out that if I add code (MyDTOItem = New dtDTOItem) to the Page_Load event then it will set the value correctly. What I am trying to figure out is how to initialize the property object without having to do it explicitly. It has to be an extended property because I have custom Get and Set code.
Public Property MyDTOItem As dtDTOItem Get End Get
After debugging a particularly tricky issue in VB.NET involving the order in which instance variables are initialized, I discovered that there is a breaking discrepancy between the behavior that I expected from C# and the actual behavior in VB.NET.Nota bene: This question concerns a slight discrepancy in the behaviors of VB.NET and C#. If you're a language bigot that is unable to provide an answer other than "that's why you should use C#, noob", there is nothing for you to see here; kindly move along.Specifically, I expected the behavior outlined by the C# Language Specification (emphasis added):
When an instance constructor has no constructor initializer, or it has a constructor initializer of the form base(...), that constructor implicitly performs the initializations specified by the variable-initializers of the instance fields declared in its class. This corresponds to a sequence of assignments that are executed immediately upon entry to the constructor and before the implicit invocation of the direct base class constructor. The variable initializers are executed in the textual order in which they appear in the class declaration.
Contrast that with the portion of the VB.NET Language Specification concerning Instance Constructors, which says (emphasis added): When a constructor's first statement is of the form MyBase.New(...), the constructor implicitly performs the initializations specified by the variable initializers of the instance variables declared in the type. This corresponds to a sequence of assignments that are executed immediately after invoking the direct base type constructor. Such ordering ensures that all base instance variables are initialized by their variable initializers before any statements that have access to the instance are executed.
The discrepancy here is immediately obvious. C# initializes class-level variables before calling the base constructor. VB.NET does exactly the reverse, apparently preferring to call the base constructor before setting the values of instance fields.If you want to see some code, this related question provides a more concrete example of the divergent behavior. Unfortunately, it does not provide any hints as to how one might coerce VB.NET into following the model established by C#.
I'm less interested in why the designers of the two languages chose such divergent approaches than I am in possible workarounds for the problem. Ultimately, my question is as follows: Is there any way that I can write or structure my code in VB.NET to force instance variables to be initialized before the base type's constructor is called, as is the standard behavior in C#?
Columns 0 & 1 are filled from a DataAdapter from Access Database and three are added. I had this working, but I changed it to check for the column "Feed" so I could add several Locations. At first this worked,but I did someething in perfecting it and it now fails after filling the first row of the datagridview (dgvFdMed).I ran a check and the table LotsTab has 8 rows filled. Column 1 & 2 are strings and the database appears they are fine. The added columns have just been created with no value. My plan is to enter the values and then use the data from the grid.
Private Sub sfillGrid(ByVal Loc As String) Dim i As Integer Dim column As DataGridViewColumn
I need to this at runtime. I checked using Reflector and value types line like Int16, for example, should contain
[Code]...
EDIT: only for the example I used directly GetType(UInt16) but in real code this part is substituted by an instance of unknown-at-design-time .NET Type
If a AJAX-Enabled WCF should return an Object with a Date Property which is Nothing a Request to this Service fails.[code]Chrome displays on this call the following error message: "failed to load resource".Has anyone an explanation/idea for this behaviour and how are you supposed to prevent this problem?
There are several times in my code when I need to determine the width of some text. Under VB6 I would use the .textwidth() method pretty much any time I wished.Under VB.NET it appears that the paint event is the only place I can gain access to an initialized graphics object and from that the measurestring() method.Do I have to use a flag in the paint event when want to auto-resize my splitterbar position or is there another way?
I am struggling with VB.NET's graphics paradigm.There are several times in my code when I need to determine the width of some text. Under VB6 I would use the .textwidth() method pretty much any time I wished.Under VB.NET it appears that the paint event is the only place I can gain access to an initialized graphics object and from that the measurestring() method.
I am writing a school project in VB2005 and am trying to hook up a second combo box that gets its information of what to display from the first combo box. My application is where a student takes a "test" but they can choose what instructor they want in the first combo box. From there, they choose from a test of what each instructor offers in the second combo box. As of right now, my first combo box works great and my second combo box has nothing in it. Just a note, when I debug, it shows my iUserID value as 0.
I need to create a function which have either 1 parameter with a string as data type or 2 parameters with double as data type.Something like the substring method.
I am trying to perform a simple bound connection between an Access database and a text box on a form. This is actually Chapter 18 of the "Microsoft Visual Basic 2008" book.I get the same error message when trying to create my own project "MY ADO Form" or the "ADO Form" project supplied from the DVD provided with the book. I am running the 90 Day Trial Version of Visual Studio 2008 with SP1 and Net 3.5 SP1.
My operating system is the 64 bit Version of Vista with all updates.The error when I try to run the application in the debug mode is:"A first chance exception of type 'System.InvalidOperationException' occurred in System.Data.dll"and as a result no data shows up in the text box from the database and the data selection bar is grayed out in the form. The underlying database "Students Data Set" appears to be fine as I have seen the correct data for the fields "Instructor" and "PhoneNumber" prior to running the program and when connecting with the database.
I'v designed a ms access database table with one field having Datetime datatype. I can Insert data into it from vb.net front end by trns_dt DateTime.Now.DateBut when I fetch records from the tableand assign the dataset datasource as da, it shows datatype mismatch error.
I have tried everything I can to get beyond this error which shows below as <<<<< error here. It is trying to fill a dataset from a data adapter. If I change the SELECT statement to just SELECT * FROM xTable I get the correct number of records in each table. But anytime I try with a more complex statement I get the error message shown below which indicates System.Data.Common.DbDataAdapter.Fill(DataSet dataSet. I've completely erased all data and entered a new set of test data so I know there is no problem with relationships. Each table has primary key which is foreign key in other table. IS there something wrong with the Imports section: Imports System
I have two Datagrids, One grid has all the customers garments on it with style number and contact length. The other grid has the users who have garment issued to them. the style number is in both grids. I need to loop through the users grid and say if the contract number is 1 from the first grid then the contract date on the second grid will be todays date + 365 days (year contract) I have looked at using a stored procedure and also a for each command but I am just getting stuck with it all. [Code]
I have a webbrowser.So once webbrowser is completed then it should add the specified value in [TEX] [/TEX] value in php.When webbrowser is completed then this http://screensnapr.com/e/LCgzhP.png value will be our specified value.I tried using this on webbrowser completion. Webbrowser1.Document. getelementbyid("the_file").SetAttribute("value", "C:/test.jpg")
I'm using LINQ to Entities to generate typed result sets in VB.Net. I've got a generic Report class as follows:
Public Class Report Public Property Name As String Public Property SQL As String Public Property Type As String End Class
Then in the calling scope I want to have code that does something like:
' create my data context Dim context As New MyAppEntities ' get a report object out of a dropdown list
[Code]....
So far I'm finding that .Net won't let me set the type in the (Of Type) clause on the fly at runtime.
Does anyone know how to do this?
I've tried changing the Type property of the Report class to an object of type Type, but that doesn't work either.
BTW, I know there are alternative ways to accomplish the same thing, but I'm working with external constraints that make this what I've got to work with right now.
I have a program that calculates commission, but if the commission is nothing then I do not want it to show a zero commission. I want a message box to show a message that there is no commission earned.
My colleague gave me a DLL that manage all database business. I wanted to invoke a function that uses Stored Procedure and return the search result. In the function receive a parameter type in ystem.Data.IDataParameter[]. Below is my codes.
