VS 2008 Convert Access Database Null Values To String Type?
Jun 7, 2011
i am working in windows appl vb.net 08. And i am working in Access DataBase.I have one Table Called "Person" . In this "Person" Table one Column Name Called "OtherName". In this Column binded in one of the Combobox in a Form.But the Problem is "OtherName" Column having the Null Values.Before i bind this Column to Combobox i want to convert this NULL Values to String. Why i need the values in STRING means , In my code i using this Combobox as a filter in SQL Query.If i didn`t change the Null Value to STRING , The Combobox SelectedText or SelectedValue is Showing Nothing. So i am not able to get the Record.
Whn i write a Sql Query to Combobox and apply filter in WHERE statement like Combobox.Selectedtext or Combobox.SelectedValue In "Selected Change Committed Event" then i should get the record in the Output right but unfortunatly i am not getting the Record. The Record Count in DebugPrint showing 0.
[Code]...
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Jan 16, 2011
Considering that Grade.firstExam, Grade.secondExam, and Grade.finalExam are all TEXT and not numbers, i can't get the exact solution to convert null values into Zeros. I already tried to use NZ() but it returns an error message (Undefined Function 'NZ' in expression)im using VB.net with MS Access as my database. i also imported System.Data.OleDb Namespace.
[code]...
How can i convert empty string or null that exist in the field?
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Jan 5, 2010
How update the Access database in VB.Net with NULL values using OLE DB command
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Jul 26, 2010
I am attempting to use the DateTimePicker and then add a day to each iteration in a For/Next loop. That seems to work fine and I can verify with msgbox that it is happening. However, I also need to write the date in string format to an Access database using INSERT INTO. However, when the code is ran, I get a "syntax error (missing operator)". Code is below. Can someone help please? I have tried all I know to do.(Please disregard the additional values in INSERT TO, I have verified they are working properly)
[Code]...
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Nov 2, 2010
I am a total beginner to Visual Basic and have a project to conduct a survey for my company. The Answers of the users need to be populated to the database. So far, all I've managed to do is to define a string which will have the answer to be updated into the access table. How am I supposed to pass the value?
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Mar 29, 2009
I am trying to utilize the access database, but I'm getting an error message: Value cannot be null. Parameter name: dataSet
[Code]...
That's the code I'm using, why I'm getting this error?
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Dec 16, 2009
Is there any way to convert null terminated string to normal string.I mean I can easily make a program to find the location of vbnull but there has to be a built in function for that.
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May 23, 2010
foreach (PropertyInfo PropertyItem in this.GetType().GetProperties()) {
PropertyItem.SetValue(this, objDataTable.Rows[0][PropertyItem.Name.ToString()], null);
}
In one of the loops i get this exceptional error:
Object of type 'System.DBNull' cannot be converted to type 'System.String'.
The error occurs because one of the fields in the database has no value (null), so the string property could not handle it. How can I convert this null to string? I'm trying to avoid checking on every loop is current value is null or not.
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Oct 15, 2009
Ive created one database Sql Server Compact Edition 2005, with one table ("Cliente") I know that I can created my database good, but i have a problem saving information since three textbox, in my table(With columns "Nombre" "Apellido" "Cliente". In my form there is a button save ("Guardar"). When I do click in my button appear the next message : "The column cannot contain null values. [ Column name = Nombre,Table name = Cliente ] " and happen the same with apellido and Id_Cliente. And this happen becouse my code cant save the information....
This is the code
Option Explicit On
Option Strict On
Imports System
Imports System.IO
Imports System.Data
[CODE]...
And the code for my button is:
Private Sub cmdguardar_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdguardar.Click
Dim myconnection As SqlCeConnection
Dim mycommand As SqlCeCommand
[CODE]...
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Mar 30, 2010
I tried this
Dim value As
String
Dim returnValue As
[code]....
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Jun 9, 2012
I doing a project for my office. In that I am showing the values and strings from a particular table based on the date range and vendor selection. It is working fine with the date range. Except within the date range if the particular reader has no data it throws an error message like dbnull string.
[Code]...
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May 22, 2009
Did anyone knows where can I upload a folder so my programe to be able to download an update from there???
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Nov 19, 2010
i am getting all filenames from a directory.parsing out the directory names & the .vb extension then converting those filesnames to classes.Every file in the LPCriteria direcotry is its own class with a "Evaluate" function.[code]
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Nov 17, 2011
I am working asp.net vb application. I have set of values to be inserted to Database.But their some fields are optional to be filled. I need to check the textbox empty. If empty I should not enter the value to Database. How to work on this?
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Jun 8, 2012
im a newbie in vb.net and i am using vb.net 2008 express edition,,i am creating a project which is importing csv data in my database,
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Mar 9, 2010
I want to create a custom date type. I want to allow null values, and return a string to the user if no date if specified.
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Jan 1, 2012
I am looping thorugh a datatable and and printing each row to the console and I keep on getting a dbnull error. I inserted an if statement in my loop to try and catch it, but I can't seem to get it to work.
[Code]...
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Aug 28, 2009
In a VS 2008 ASP.net 3.5 aspx.vb file, Response.Write(DDL.SelectedItem) worked very well.But "Dim filenameDDL As String = DDL.SelectedItem.Text" did not. Then I tried the following codes and found the problem -- Conversion from type 'ListItem' to type 'String' is not valid.
[Code]...
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Feb 10, 2010
I want to add a null binary field in Database.[code]...
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Jun 12, 2010
. I get this error: "Cannot convert lambda expression to type 'string' because it is not a delegate type" - keyword select become underlined in blue
[Code]...
Above code should displays drop list of employees first name and last name in a combo box
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Jan 4, 2012
I have a couple of textfields in a Windows form. One of these textfields is allowed to be NULL. When I enter a value for every field, it is all inserted, no problem. When I leave the field (txtGewicht) blank, I can't seem to be able to insert NULL in Access Database.
If Double.TryParse(txtGewicht.Text, 0) Then
klant.Gewicht = Double.Parse(txtGewicht.Text)
Else
[Code]....
This is what I get:
"Cannot set column 'Gewicht' to NULL, please use DBNull instead"
So I changed 'Nothing' to DBNull.value, but it then tells me that System.DBNull cannot be converted to type Double.
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Apr 23, 2012
What is the quickest way to convert a string value of a URL to type URI? VB.NET please..
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Aug 2, 2011
I need some thought input on how I can take my string of HEX values and convert them to ASCII according to the specifications below: A function would be ideal since I need to quickly decode about 250 records all having 20 thresholds to record.[code]
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Mar 14, 2011
I'm writing an asp.net page with a simple registration form that connects to my access database and inserts the values in the table. So I have my database, my registration page, everything looks fine in my code, but there's a syntax error I can't seem to figure out. When I go on my webpage and click submit, it says : Syntax error in INSERT INTO instruction.
Here's my code:
<%@Page language="vb" explicit="true" debug="true"%>
<%@Import Namespace="System.Data"%>
<%@Import Namespace="System.Data.OleDb"%>
[CODE]...
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May 1, 2012
fast way in VB to go from a string to a generic type T constrained to a valuetype (Of T as Structure), when I know that T will always be some number type?This is too slow for my taste:
Return DirectCast(Convert.ChangeType(myStr, GetType(T)), T)
But it seems to be the only sane method of getting from a String --> T. I've tried using Reflector to see how Convert.ChangeType works, and while I can convert from the String to a given number type via a hacked-up version of that code, I have no idea how to jam that type back into T so it can be returned.
I'll add that part of the speed penalty I'm seeing (in a timing loop) is because the return value is getting assigned to a Nullable(Of T) value. If I strongly-type my class for a specific number type (i.e., UInt16), then I can vastly increase the performance, but then the class would need to be duplicated for each numeric type that I use.
It'd almost be nice if there was converter to/from T while working on it in a generic method/class. Maybe there is and I'm oblivious to its existence?
Conclusion:Testing the three provided implementations below and my original DirectCast/ChangeType form, @peenut's approach of using a prepared delegate to fetch the Parse method from a basic type works. No error checking is done, however, so implementors need to remember to only use this with valuetypes that have a Parse method available. Or extend the below to do error checking.
All runs were done on a 32bit system running Windows Server 2003 R2 with 4GB of RAM. Each "run" is 1,000,000 executions (ops) of the method to be tested, timed with StopWatch and reported back in milliseconds.
Original DirectCast(Convert.ChangeType(myStr, GetType(T)), T):
1000000 ops: 597ms
Average of 1000000 ops over 10 runs: 472ms
Average of 1000000 ops over 10 runs: 458ms
[code]....
Comparatively, peenut's approach is almost 200ms faster when executed 1,000,000 times in a tight loop, so his approach wins out.
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Mar 6, 2010
I need a function that will convert a type to a string, for example[code]...
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Jan 3, 2011
Is there are any way to convert boolean type into "ON"/"OFF" using string formatter
Like:
Dim inpValue as Boolean
Dim outValue = String.Format("0:ON;OFF", inpValue)
' should show OFF as output
I cannot use code or IFormatProvider
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Feb 15, 2010
i m trying to run a query on an MSAccess table, but it does not give me any count but only 0.
There are 3 null values which i should be getting but it does not give me the result. This query works perfectly in MSSql Server 2008.
the query is :
Quote:
SELECT COUNT(*) AS Cntr
FROM (Modul m LEFT OUTER JOIN
Relation r ON m.Mod_Name = r.von)
WHERE (m.[group] = '')
I need a workaround for this but am unable to find one.
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Apr 3, 2009
I have a DataGridView1 populated by sql searches. On the rare occasion that nothing is returned, my app cannot make use of data so I'm trying to check for null values. My code below is not correct because IsDBNull is not a member of the of the DataGridView1.
If DataGridView1.SelectedRows(0).IsDBNull Then
MsgBox("Nothing to display")
Exit Sub
End If
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Jan 6, 2011
Does anyone know of a fast way in VB to go from a string to a generic type T constrained to a valuetype (Of T as Structure), when I know that T will always be some number type?This is too slow for my taste:
Return DirectCast(Convert.ChangeType(myStr, GetType(T)), T)
But it seems to be the only sane method of getting from a String --> T. I've tried using Reflector to see how Convert.ChangeType works, and while I can convert from the String to a given number type via a hacked-up version of that code, I have no idea how to jam that type back into T so it can be returned.
I'll add that part of the speed penalty I'm seeing (in a timing loop) is because the return value is getting assigned to a Nullable(Of T) value. If I strongly-type my class for a specific number type (i.e., UInt16), then I can vastly increase the performance, but then the class would need to be duplicated for each numeric type that I use.
It'd almost be nice if there was converter to/from T while working on it in a generic method/class. Maybe there is and I'm oblivious to its existence?
Conclusion:Testing the three provided implementations below and my original DirectCast/ChangeType form, @peenut's approach of using a prepared delegate to fetch the Parse method from a basic type works. No error checking is done, however, so implementors need to remember to only use this with valuetypes that have a Parse method available. Or extend the below to do error checking.
All runs were done on a 32bit system running Windows Server 2003 R2 with 4GB of RAM. Each "run" is 1,000,000 executions (ops) of the method to be tested, timed with StopWatch and reported back in milliseconds.
Original DirectCast(Convert.ChangeType(myStr, GetType(T)), T):
1000000 ops: 597ms
Average of 1000000 ops over 10 runs: 472ms
Average of 1000000 ops over 10 runs: 458ms
[code]....
Using System.Reflection and calling InvokeMethod to get at the Parse method:
1000000 ops: 12213ms
Average of 1000000 ops over 10 runs: 11468ms
Average of 1000000 ops over 10 runs: 11509ms
Average of 1000000 ops over 10 runs: 11524ms
[code]....
Konrad's approach to generate IL code to access the Parse method and store the call into a delegate:
1000000 ops: 352ms
Average of 1000000 ops over 10 runs: 316ms
Average of 1000000 ops over 10 runs: 315ms
[code]....
peenut's approach of using a delegate to access the Parse method directly:
1000000 ops: 272ms
Average of 1000000 ops over 10 runs: 272ms
Average of 1000000 ops over 10 runs: 275ms
[code]....
Comparatively, peenut's approach is almost 200ms faster when executed 1,000,000 times in a tight loop, so his approach wins out. Although, Konrad's wasn't far behind and is itself a fascinating study of things like ILGenerator.
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