Been a while since I did any VB work, and have started a new project that is a Windows Service that will update a database using multiple threads. I am testing this out with a dataset that consists of a "device name" and a "device IP", pinging the device, and attempting to update the device's "status".
I have it working in a single-thread type configuration, but would like to be able to ping and update different records across multiple threads (for obvious reasons).
The problem I'm having is with the logic mainly. When the service is started, I get all the devices from the database and fill a DataSet. From there, I am looping through the dataset's rows, pinging each device and updating the record. I know how to spawn multiple threads, but I do not know how to keep track of updating the correct record and also making sure that all records are checked in some kind of order. Like, if user specifies 5 threads, I need it to get record 1, thread finishes, gets record 6 (while other threads execute), or something like that.
Note: this does no interface updating or anything like that. Only updates a database record's field value.
I have this class and I have a loop that launches multiple threads from the same class. This is all done from the main form.Now I want to update the richtextbox on the main from these classes.I have tried those begininvokes etc etc and nothing worked, no error but no output as well.Here the code for launching the threads :
Private PingObjects(100000) As Account 'Account is the class and login is the sub in it... PingObjects(I) = New Account Threads(I) = New Threading.Thread(AddressOf PingObjects(I).login)
And to update the rtb, im using MainForm.log.text = "....." Nothing happens, no error.I have tried using the begin invoker method as well.
I am considering a piece of code that will manage access to a collection object from multiple threads - add, update, remove, clear. OK ... so I have put a sync lock within each method, but what is not clear from the MS documentation is exactly how the sync lock is behaving. Is it locking the piece of code it wraps? Or is it locking the object? And if it is locking the object a private static object should lock out any code locked on the object within all instances of the object? i.e. if an add operation is underway, an update, delete or clear will wait for the lock to be released.
Finally, if I have multiple threads contending for the sync lock, how is the release managed? First come, first serve? random (from my p.o.v)? Is there a chance that two separate threads could blunder into 'locked' code simulataneously?
Is it safe to update an SQL database from multiple threads at the same time? I have a method which runs on up to 25 thread pool threads at the same time and it attempts to write to a text file and update an SQL database - I assumed that writing to the file would not work properly if all threads tried to write to it at the same time, so I have used SyncLock for that part of the method. Just wondering if I need to do the same thing for the part of the method that updates the SQL database? or is the framework (or SQL server) smart enough to either execute multiple update statements on the same table at the same time without a problem or queue them?
I just had a new, last-minute idea on to take on a task, so I am running to StackExchange for quick help.
What I want to do is execute a series of methods right in a row, each in their own threads. I want the application to wait until all of these threads are completed, after which the program will resume. It also has to use managed threading (thread pool).
What quick examples could you provide to help me along the way? If it's too complex, what things should I know about so that I can Google it on my own?
Ive created a form to add/delete/update records in a database ,but when i try and open the frm i get a NullReferenceExceptionUnhandled error, below is my code, i cannot for the life of me see where i've gone wrong, but maybe someone else can spot it?[code]
I am using Visual Studio 2008 for creating a Winforms app. I have connected a database to it called XStats. There is one table in it called XGames and in that table 2 fields, XIndex (the primary key field) and GameNumber. Using the following code I can add records to the database, the data is taken from a text box, but once added I cannot view them unless I shut down the app and restart it.
con.ConnectionString = connectionString con.Open() Dim cmd As New SqlCommand
The existing records in the database are displayed on the form in detailed view via a binding navigator. How can I make it so that I can view all the records in the database, even those that are added during the current session. As will be obvious, this is my first attempt at creating and using a database with a win forms app,
how to update records on an existing access database using vb.net with just a textbox and a command button and how a specific record of a field can show up in a label or a textbox
i connected vb.net to my access database by just clicking on "add new data source">>"new connection">>"microsoft access database file" and just continue..tested connection and done.
you can see in the screenshot of my form, by default the left side textboxes are disabled but they're enabled if the user checks the checkboxes and disabled again if unchecked.
assuming that the textbox is already enabled and i want to enter a value in the Brewed Coffee area of the form...for example 5. when i click on my Submit button the value of that particular record in the database will be updated, so in my table the value of the quantity field in Brewed Coffee will be 5.
another thing is that how can i see a particular value on a label or textbox from my database like on the Prices area. in my database if a product's price is 80 then it should show a 80 in the label. the values of the prices from the screesnshot of the form are not the ones on the database xD i just typed them in.
I have problems with the updating and deleting of records in database. I'm using ObjectDataSource and the GridView to display the results in the database. Below is the codes for the update and delete (in the DAL (data access layer). BTW, I'm doing 3 tier architecture in VB.
'update the records accordingly in the database. Public Function UpdateBooks(ByVal title As String, ByVal borrowDate As String, ByVal dueDate As String, ByVal NameBorrower As String, ByVal book_id As Integer) As Integer Dim connectionString As String = My.Settings.dbConnection [Code] .....
I don't know why, but every time I try to update (by clicking on the update button), every thing is not updated, the page would refresh then the records still remain the same in the GridView. As for delete, when I clicked on the 'delete' button, the record is not deleted, it still remains there.
These are the codes in the (BLL (business logic layer)): Public Function getUpdateBooks(ByVal title As String, ByVal borrowDate As String, ByVal dueDate As String, ByVal NameBorrower As String, ByVal book_id As Integer) As Integer Dim ds As Integer = UserDA.UpdateBooks(title, borrowDate, dueDate, NameBorrower, book_id) Return ds [Code] .....
I display my records using datagridview...I have also Save button which is intended to update any changes I make via the datagridview.I got this error whenever I type something in the address column "Update requires a valid UpdateCommand when passed DataRow collection with modified rows."[code]What code do I put so that whenever I highlight a row and click delete button or press delete key selected records will be deleted from datagridview as well as my database will be updated from any deletion?
how to update records from 1 text file into 2 different sql database.
Name of the sql Table is Payment2SQL_Success_P() & Payment2SQL_Success_E() is the code below is on the right track. Select Case "AGENCIES" Case AGENCY_AV Or AGENCY_SR Or AGENCY_IP Or AGENCY_TM Or AGENCY_MS
I'm using visual basic 2008 express edition by linq to sql for my database operation such as edit records. I did not use any sql server but I'm just using the built-in sql server within the visual basic 2008 express. I tried to revised the codes, no error in syntax but there's an error at runtime and it pops-up a window message saying its error message. What I want is to edit the records which were retrieved from the database into the text-boxes and when you click the button5 whatever the new value on the text-boxes should replace the previous one.The Account field is the field in my Table1 in memrec.dbml which I set up for primary key is true and the rest of the fields are false in its primary key.[code]...
I'm using visual basic 2008 express edition by linq to sql for my database operation such as edit records. I did not use any sql server but I'm just using the built-in sql server within the visual basic 2008 express. I tried to revised the codes, no error in syntax but there's an error at runtime and it pops-up a window message saying its error message. What I want is to edit the records which were retrieved from the database into the text-boxes and when you click the button5 whatever the new value on the text-boxes should replace the previous one.The Account field is the field in my Table1 in memrec.dbml which I set up for primary key is true and the rest of the fields are false in its primary key.The code below still found an error when you run the program and it pops-up a window which says:
NotSupportedException was unhandled - Sql server does not handle comparison of NText, Text, Xml, or Image data types.It highlights a yellow background on the line:
These are what I see on each field's property on Table1 in memrec.dbml property window:
Access - Public Type - String(System.String) Server Data Type - Text[code]........
How do I insert,update,and delete records in vb.net 2008 from a Access 2007 database?Really, I figured out how to add records - but I cannot delete or update records. Any pointers, website tutorials, etc?Also, I am binding the database table to Listbox which is working, but I need to update the listbox with deletion and update changes too...
I have used this form to add new records on my database(ms access) in my database I have a column name 'ID' which is my primary key 'ID' is set as auto number. Now I am having a trouble on creating my update and delete button it's always saying "cannot be delete/update"
Here's my code on add, update and delete Public Sub SaveRecord() Try Dim dbConn As OleDbConnection Dim dbInsert As New OleDbCommand Dim str1, str2, str3, str4, str5, str6, str7, str8, str9 As String [Code] .....
Note my add is working perfectly fine. I just can find the error on my delete and update. Also I have used this to view it to my datagrid I don't know if its the right thing but it's working fine too. 'declared dbpath globally' Dim dbPath As String = "Provider=Microsoft.Jet.Oledb.4.0; Data Source=../VG.mdb;Persist Security Info=False" [Code] .....
Another thing is how to code each textbox and combobox to bind it to my records so that when I click on the datagridview each column will be distributed on each respective textbox.
With the following code i am able to update record in the first row. Can some tell me what i have to replace in this code to update a record for a selected row. I have a field "Sr_No" with primary key.[code]...
This is the hardest part of LinqtoSql database handling operations in visual basic 2008 I ever encountered,w/c is the update operation cause Ive been posting this thread several times from the other forum site but noone yet was able to answer my question,examples were given but its not efficient cause it won't specify based on the codes i gave and i know its not easy but im still hoping that one of the answerers of this forum will be able to resolve this particular linqtosql operation codes. I used textboxes in manipulating all data into the database such as displaying records, adding records, & updating records, basically I used with textboxes in doing those database operations. I will give you 3 block of codes w/c corresponds those database operations I used and differentiate from each other inorder for us to determine why one of them has no progress or won't do its operation w/c is the update operation...
*************Block of Codes#1(Adding Records)************* Private Sub Button1_Click(------------------) Handles Button1.Click Dim db As New memrecDataContext()
I would like you to identify,differentiate, or troubleshoot the block of codes#3, or anyhow, why it has no progress at all or it won't edit and change the records but it runs and no error in regards with its code, and the other 2 blocks of codes were able to successfully do its operations.I was just wandering why only the block of codes#3 is not doing its operation successfully when you change the record being displayed in the textbox.Is there a possible way to edit records in the textboxes?If there is.... Is it possible to debug the block of codes#3 to successsfully do its operation? If you could possibly give an example,can you based it on the block of codes#3?
I'm using Visual Studio 2005, and MSSQL.I need to print records from database on the preview document according to my select statement condition. I have no problem printing one page, but when the records exceed one page it does not go to the next page. I've tried setting e.morepages to true, but it just prints infinite number of pages with the same result. I'm guessing the problem is with my pointer, where the if-else condition is always true so it just keeps printing.
i have a simple application which can create/update/delete/search records using Access database. If i add a record, save it, then close the application and run it again and search for that record, it appears. However, when i write some code to my application, nothing to do with the search function, and i run the application the record is not found. For example i added a button to clear the textfields, and when i ran the application the records i have added earlier were not found.
I am writing an application that does a number of different things with data downloaded from hardware which is monitoring the power used in my home and produced by my PV Solar array. I have run into a roadblock early on, because I cannot seem to get new data into an Access database that I have linked to my application by means of a DataSet. I have checked the DataAdapter's InsertCommand, DeleteCommand, and UpdateCommand definitions (created by the DataSet Wizard), and they seem to make sense, and nothing is throwing exceptions or otherwise making VB complain, but new rows added to the dataset are not being added to the database.