C# - How To Avoid A Database Race Condition When Manually Incrementing PK Of New Row
Mar 30, 2009
I have a legacy data table in SQL Server 2005 that has a PK with no identity/autoincrement and no power to implement one. As a result, I am forced to create new records in ASP.NET manually via the ole "SELECT MAX(id) + 1 FROM table"-before-insert technique.Obviously this creates a race condition on the ID in the event of simultaneous inserts.
What's the best way to gracefully resolve the event of a race collision? I'm looking for VB.NET or C# code ideas along the lines of detecting a collision and then re-attempting the failed insert by getting yet another max(id) + 1. Can this be done?
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Jan 21, 2012
I use a worker thread to do the procedure of query and fill the datasetAnd I use 3rd party component called DevExpress XtraGrid: GridControl to view the query outputI don't forget to use invoke and delegate to set the GridControl.datasourceOn Timer.Tick(), the thread is started and the procedure is called user has scrolled down the GridControl, even only one scroll value instead,and then the Timer.Tick() fired, I gottwo errors randomly. Mostly aNullReferenceException error and eventually anInvalidOperationException error
************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
at DevExpress.XtraGrid.Views.Grid.ViewInfo.GridViewInfo.UpdateCellAppearance(GridCellInfo
[code].....
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Jun 7, 2012
im having problems with IP To country code, it checks country on .dat file, and it gives this error.Probable I/O race condition detected while copying memory. The I/O package is not thread safe by default. In multithreaded applications, a stream must be accessed in a thread-safe way, such as a thread-safe wrapper returned by TextReader's or TextWriter's Synchronized methods. This also applies to classes like StreamWriter and StreamReader.
My
Dim country As String = Me.geo.lookupCountryName(DataGridView1.Item(1, count).Value)
DataGridView1.Item(4, count).Value = country.ToString
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Jun 4, 2011
i want to start my coding immediately about linking the database in vb...but i dnt knew how...hw i can lnk my database...
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May 14, 2011
Protected Sub GridView1_RowCommand _
(sender As Object, e As GridViewCommandEventArgs) _
Handles GridView1.RowCommand
If e.CommandName.CompareTo("command") = 0 Then
Dim itemID As Integer = Convert.ToInt32( _
GridView1.DataKeys(Convert.ToInt32(e.CommandArgument)).Value)
[Code]...
Basically, it doesn't work and I don't get it. I've been trying to figure this out for a few days now and I can't see what I've done wrong. As you can see I'm trying to manually update a field in my database with the value of (originalvalue)+1 when the user clicks the buttonfield of the corresponding row.
I guess what I'm asking is if anyone can point out any mistakes, please do, or if there's a better way to do this (without having to go through all the DAL/BLL BS)
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Jul 7, 2009
I have created a local database (.sdf) and added a few records. What I really would like to do is connect to the database manually and load the records in a listview. Anyone with some tutorials?
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Sep 24, 2010
I want to do a task with a function controlling database with vb scripting. My form will include textbox, button and datagridview to view the database table manually without add from the microsoft access or other..how i want to make the table appear when i put a number into the textbox that refer to the number of row and column and then click the button to create the database table? Besides, how to rename it using textbox?
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Sep 18, 2009
I'm building an application that is intended to function off and online using the new Local Database Cache functionality included with Visual Studio 2008. My issue however does not pertain to that directly, as I have a pretty good understanding of how to use it and how it functions. My issue is with getting an understanding on how to directly write to a SQL database.
Most of the tutorials, videos and education available when it comes to databinding makes the assumption that I need my application to pull data and edit it, but in my case all I really need (in fact intentionally all I want) is for the application on Submit to write data that it pulls from the form as a new record in a SQL table.
Here is what the program looks like now.
Public Class StatCom
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
[Code].....
At the moment the program simply does a status check for connectivity and wether it can ping the server (in this case the SQL server) for the purpose of displaying a online or offline status in the form.
I follow it up by making the status checks.
Finally I declare all the various fields I want to capture and write to the database.
What I want to do now is have a SUBMIT button that on click takes all the data in the form and writes a new record to the database I have already setup and have data connection to.
I know that the code has to be written using the .recordset functionality, but I haven't found any could tutorials on the subject that have turned on the light upstairs.
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Sep 15, 2009
I've been messing around trying to get an INSERT statement to work, and because of this, it has created lots of records in my database that I dont need or want.
The problem is, when I open up the table by right clicking on it in the database explorer and selecting "Show table data", I click on the record I want to delete and the following error comes up in a message box[code]...
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Sep 13, 2009
Is it possible to manually save data from my dataGridView to my SQL server database table?
if it is possible can some please tell me how to do it because i don't like using the data sets and reader VB has because it doesn't give me full control over the procedure.
please see the code below it all works fine its just the last two line im struggling with, which is where i am trying to save the data from the two columns in my DataGridView [code]...
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Mar 15, 2012
how can i avoid data duplicate in the database?i mean if i add in the fields that has been already save it will still save.i don't know how to query or filter not to add the same info.i have the code below but it still save if i input same as already in the database.[code]i want is to query first before it add the data to avoid same info.
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Jan 29, 2011
How can i avoid the duplicate values in the Access Database?? I am working in VB.NET, to create DataEntry Form. I have Combobox. When enter the value on Combobox and press OK button then the value should check on the database , if the value is not there then it should save on the db. else the Missage will give "It is Saved".
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Aug 1, 2011
For a race, I am trying to evenly disperse the heats for smaller race groups within those of larger race groups. I do not want the smaller groups to finish too early and I am also trying to minimize groups running back to back heats.
As an example:
Group A has 4 heats
Group B has 2 heats
Group C has 1 heat
The resulting schedule would look something like this:
A1 B1 A2 C1 A3 B2 A4
To complicate things, there could be any number of race groups and each race group can have any number of heats.
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Dec 29, 2011
Basic out line connecting to an irc server. We connect to this server using a TCP client on a separate thread from the UI. Now the raw numeric for the MOTD is "372" so when our streamreader reads this value from the worker thread it raises it's value and displays it to a RTB. Now my issue. When i connect to a server i wait till raw "372" before i check to see if i need to join a channel. But a lot of servers have more then then one line MOTD each sending there own "372". So if a server has a long MOTD that could mean over 100 "372".
Now while it does not effect the UI of my app i wish to move the "372" to it's own thread from the current worker thread. But thats the problem. How do i move the MOTD to it's own thread when it's still being read.
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Jan 23, 2009
I have been given an assignment for my VB.Net class. Basically,given the race car's weight, horsepower and distance traveled,determine the time.I am going a couple of steps further...
(1) I am including two pictures of competing race cars at the staging area and a short track to travel (makes the assignment more interesting). I would like to know if it is possible to provide an animated light sequence of the Race Tree (staging lights, 3 sets of amber lights, and the green light) with a timer activating the start of the race.
(2) I would also like to incorporate a "sound" track of a race car as the two race cars proceed to the finish line. I realize that the user may enter any distance for the race. Regardless of the amount of time it takes to run the track (if given a long distance),I'm going to calculate the total time to span just 15 sec. Again, I would like to know if it's possible to incorporate these two
separate modules into my program using the Window's form application?Also, what resources should I study to gain knowledge on how to
execute the two modules?
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Feb 15, 2012
So I have an application which uses MSSQL server as datasource. Is there anyways I can avoid using any database server and use a local file as datasource ?
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Nov 4, 2009
I am building a program where all the inputs (10) required from the user are asked on one form. Since it is not possible to let fields blank on the database, I would like to know how can I build an 'IF' saying that if all fields are full, then the database CAN save all the input. So that if there are any field blank, it won't save. I just dont know how to do the database condition. Thats all.
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Jun 8, 2010
I am using ExecuteReader commands to read records in large external databases. Part of my program logic requires that a condition of the database be examined without reading another record - for instance, I want to know if the database has reached the end without reading an additional record.
[Code]...
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Jun 7, 2011
Possible Duplicate: Way to get unique filename if specified filename already exists (.NET)Have a look at the following code:
Dim counter As Integer = 0
While System.IO.File.Exists("C:DesktopSample.xls")
counter = counter + 1
[code].....
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Jul 18, 2010
I'm trying to increase the value of a registry entry by 1
HKLMSoftwareMyApp
Key = Test
Value +1
[Code]....
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Jan 27, 2011
i'm doing this for auto incrementing i called the last value in a row from a database for say, its p-0004 what i wanna do is take p-0004 and add 1 into it to make it p-0005 sorry for my stupidity, i tried using the trim method i used in vb 6 but there was an error like "read only property" something
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Aug 16, 2011
i'm doing this for auto incrementingi called the last value in a row from a databasefor say, its p-0004what i wanna do is take p-0004 and add 1 into it to make it p-0005sorry for my stupidity, i know this is a noobie question but hey, i'm a noob
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Aug 5, 2011
What is the += used in this code doing? Is that incrementing the loop?
Public Class Form1
02
Public Structure Family
[CODE]..........................
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Jul 11, 2011
I am trying to make a simple port scanner to scan a rang of IP's so like 192.168.4.245 to 192.168.5.100. I am using Visual Basic.Net 2010 and am having trouble converting the IP from a String to a Long so that I can increment it and convert it back to a String. For some reason VB.Net 2010 doesn't include the winsock controller and therefore I am having problems finding a method that works similar to inet_addr() which makes conversion much easier. I found an example on one of the forms here
Code:
Private Sub Command1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Command1.Click
[code]....
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Feb 1, 2010
When you access a subroutine by one or more other subroutines each time the variables are zeroed like 'n' below. How can I keep n saved so main can increment n each time.
Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
[Code]....
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Jun 20, 2009
I've been looking into this problem for a few days now and i can't find exactly the code that i want.I want to run a procedure using an incrementing matrix. If the Matrix that was used is correct then the correct matrix is shown.
the process is get first iteration process if incorrect repeat with next iteration correct end the issue is with the iterations and breaking out of them the matrix length, depth and iteration step can vary.
this is best shown in an example
length = 5
high = 3
low = 0
step 1
the iterations should look like
[Code]...
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Feb 17, 2009
I have created a table with the following fields
loan_id (PK)
loan_date
loan_return_date
loan_user (FK)
i have set the loan_id column to increment in steps of 1, but when i add a column in visual studio 2008 express it auto increments in minus steps -1 -2 -3. it increments in positive numbers?
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Nov 15, 2011
I have some nested objects arranged like this:
Process
Persons
Workflows
Tasks
So you have one Process. Then multiple Persons can be added to and multiple WorkFlows can be added Process as well. Multiple Tasks can be added to each WorkFlow but I need a way to tie which Person is doing each task. I basically need a way that for each Person added to the Process it, in it's constructor, assigns a Person.ID property that can then be assigned into each Task's PersonID property...
Dim myProcess as New Process()
Dim myPerson as New Process.Person()
myProcess.AddPerson(myPerson)
[code]....
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Jun 21, 2010
I would like to know the coding behind incrementing a progress bar using a timer.
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Nov 18, 2010
i do have a table with 3 cols, 2 of those will visible for users to enter data, the last one is needed to get inserted as the next number of the previous number.
i use the following query for insert command ,
INSERT INTO [Headers]
(GrpId, GrpName, Number)
Select (Select Case when Max(GrpId) = Null then 1 else Max(GrpId)+ 1 end from [Headers]),
[Code]....
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