Primary Key And Foreign Key - Private Locking Object For List1 And Lock List1 Whenever It's Modified
Jan 26, 2011
This is a follow-up to a previous question regarding locking on two List(Of T) objects. Suppose I have a function like this:
[code]...
which resides in a class that declares List1. In a multithreaded environment, I now understand that I should have a private locking object for List1 and lock List1 whenever it's modified or enumerated. My question is, should I do this:
[code]...
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Dec 12, 2010
I can succesfully display selected value of List1 into List2 on ItemCheck Event. But when i uncheck the item it doesn't remove the item from List2.
Private Sub List1_ItemCheck(ByVal sender As Object, ByVal e As System.Windows.Forms.ItemCheckEventArgs) Handles List1.ItemCheck
Dim i As Integer
[Code].....
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Jul 13, 2009
I have created a synchronized queue and am using SyncLock on the SyncRoot property of that queue when I invoke the Enqueue/Dequeue methods. The methods are invoked from instances of standard producer/consumer classes.Is that a proper use of the SyncRoot property?
Would it be better practice to create a private shared object in each class and lock on that instead?
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Apr 26, 2009
Ok this is what I'm stuck on:I have 2 ListBoxes and 2 Lists, let's call them ListBox1, ListBox2, List1 and List2.List1 needs to be associated with ListBox 1, and List2 with ListBox2 I loop through a bunch of accounts, add them to LixBox1 at run-time.During that loop I add each account number to List1 so now the account number is associated with the ListBox index number which is right.Now when I double click one of the accounts in ListBox1 it is added to ListBox2 (but it still remains in ListBox1), and the same index of List1 added to List 2, now the account in ListBox2 is associated with the account number at the same index in List2 you see where I'm going with this?The issue wtarts here.When I double click an account (let's say the account at the first index) in ListBox2 it should be removed from the list, so now I remove the index from List2 since it's no longer needed, but now you know what's happened right? ListBox2's List indexes have all decremented by 1 because I just removed an item from the beginning of the list, but List2's indexes have stayed the same (at least that's how it appeared when I tested it).
So basically whats the best method for keeping things in reference? I was told about list boxes in another thread of mine, but is it really the best way to go about this, I can't seem to keep everything linked together reliably.
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Oct 5, 2011
Is it possible to have a Foreign Key as the Primary Key?
<Key()>
Public Property AssignmentID() As Integer
<ForeignKey("AssignmentID")>
Public Overridable Property Assignment As Assignment
Public Overridable Property User As User
For the code above I get an error:One or more validation errors were detected during model generation:System.Data.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'AssignmentLocks_Assignment_Source' in relationship 'AssignmentLocks_Assignment'. Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be �1�.
I'm trying to create a table which has one (or none) record per assignment.
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Jan 23, 2011
I'm having some major issues trying to figure out What's going wrong with my code.
The general problem is that I can't get the foreign key in one of my child tables to populate the primary key from the parent table. I have a parent table named "ISSUES" and a child table named "ISSDESC". The primary key for ISSUES is ISS_ID which is an autonumber. The foreign key is ISS_ID in the ISSDESC table which is just a number. I'm using MS Access and an OLEDBConnection as the method. I've created the relationship in MS Access and also created the datarelation in the VB.NET code.
I am able to submit the information into the database into the two tables but the foreign key isn't being populated therefore not being linked to the other table.
I think it's probably a very simple fix, but it's been eluding me for a good 8 hours or so. I am using a dataset and 2 data adapters, one for each table.
Code:
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Apr 18, 2009
I just watched a video from Beth Messi about setting up a primary key and foreign key on a table.
I created two tables, one called customer and the other one called orders CustomerID is the primary key to the customer table OrderID is the primary ket to the orders table and CustomerID is foreign key to the orders table
Beth Messi said that this would maintain the integrity of the tables and she also mentioned something about setting up a cascade delete so that when we delete a record in the customer table, the customer's order in order table will get deleted as well.
how I can set up the cascade delete, Meanwhile, I tried deleting a customer record in customer table - a customer with orders, and I got the following error when I clicked save.
The DELETE statement conflicted with the REFERENCE constraint "FK_Orders_Customer". The conflict occurred in database "C:DOCUMENTS AND SETTINGSLOUISLOCAL SETTINGSAPPLICATION DATATEMPORARY PROJECTSWBINDEBUGTEST.MDF", table "dbo.Orders", column 'CustomerID'. The statement has been terminated.
Shall I use try catch to warn the user that the record that I tried to delete has an order? They can't delete the customer unless the orders table's record is deleted first?
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Feb 3, 2012
How do I fetch the loginID and display the student data on the textbox?E.g. I login with loginID of 18 but it only display the data of 12
Private Sub frmLibrary_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'TODO: This line of code loads data into the 'LibraryDataSet.Student' table. You can move, or remove it, as needed.
Me.StudentTableAdapter.Fill(Me.LibraryDataSet.Student)
End Sub
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May 30, 2011
I have 3 web methods in a WCF, called 'DeleteGroup', 'AddGroup', 'ModifyGroup'.Each method has its own code. I want to place a lock on code within each method, so that only one method executes at a time. For example, if 'DeleteMethod' is being executed then no request for 'AddGroup' or 'ModifyGroup' can be executed. So may be I could use something like what is below, but not very sure ? Also, where in the WCF would I declare the locker object, and would it be private, public or static (i.e. shared)?
SyncLock locker
--Delete Method Body
End SyncLock
[code].....
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Jul 20, 2009
I am using a number of tables on my application and two of which have a foreign key constraint I have set between them. When I change the account number on the main table via a combo box all of the relevant information for that table on the form is updated accordingly. However, the child table which has a foreign key reference to the Account Number of the main table is not updated when the acocunt number is changed. I have set the update to cascade in the references but still am having issues.
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Jan 22, 2012
a simple question. Given the following code:
Public Class MyClass
Private WithEvents pPerClass As PersistableClass
Public Overridable Property PerClass() As PersistableClass
Get
Return pPerClass
[Code]...
the first being a duplication of the second key, strangely obtained from a private field.
If you remove the WithEvents keyword, the pPerClass_PersistableClassID key is not created.
I am new to EF but it seems to me a strange behaviour.
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Oct 27, 2011
Currently, using Ektron CMS, i am trying to place a lock.jpg beside a protected / private content, which needs the user to login, if the link is clicked.
I am not sure how to start or go by this ?
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Mar 22, 2011
I have a problem in a multi-threaded application where I'm getting deadlocked waiting for an object to beocme available.
[Code]...
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May 4, 2012
[code]How do I update the ProdServiceID in the database using LINQ to entities?
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May 11, 2011
I'm currently using this to get an object by it's primary key value.
I'm trying to find a way to create a similar method GetByIDs where I can pass an IEnumerable(of object) and do ids.contains(pk), but there's no Contains expression.
Public Function GetByID(Of T As Class)(ByVal pk As Object) As T
Dim itemParam = Expression.Parameter(GetType(T), "item")
Return GetTable(Of T).Single(
[Code].....
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Jan 25, 2010
I'm getting an Entity Framework object collection from my Products table called oProducts. I am looping through the collection and setting the Quantity field from a separate function. Before I write out a display of the objects in HTML, I want to sort them by the Quantity. So, I am using LINQ to create a new collection and try to order from the object collection that I just modified. The modified values are definitely in the object collection and output properly, but the sort ordering isn't working on the modified field.
Dim oProducts = From p in ctx.Products _
Where p.Active = True _
Select p
[Code]....
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Jul 20, 2009
my code as follows
[code]...
result i get here is =0.7937005259841017310542661502
where as windows calculator figure is 0.79370052598409973737585281963615
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Apr 23, 2010
In the following code as you see I am defining myFile inside the timer sub; which of course is not a good idea. The FilePath is derived in form load before the timer kicks in. How can I declare myFile globally so it can be used in timer sub as well as in form load?
Private Sub tmrInterval_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tmrInterval.Tick
Dim myFile As New IO.FileInfo(FilePath)
If myFile.Exists Then
...
...
I want something like this:
Public Class Form1
private myFile As New IO.FileInfo()
'but I do not have strMessageFilePath value yet, that will be achieved in form load.
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Feb 15, 2012
Private Sub btnedit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnedit.Click
[Code]...
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Jan 19, 2009
I have a little VB 2005 Express app that acts as a gui for an application that normally runs in a cli (cmd-like) window, as follows: Code:Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim Server_Exe As String = "C:Documents and SettingsColinDesktopin 7302OpenSim.Grid.UserServer.exe"
[Code]...
1. The cmd window normally shows various status messages in colour, whereas the RichTextBox shows all messages in Black (on a white background). How can I get the RichTextBox to show the messages in the same colours that the cmd window displays?
2. As the RichTextBox fills with data, filling the box, and beyond, and the scrollbar starts to shrink, I notice that the data at the top of the RichTextBox stays there, and you would have to scroll down to see the last status message, whereas I would like it to do the reverse, i.e the last status message is at the bottom of the visible RichTextBox, and if I wanted to see the earlier messages I would have to scroll up. How can this be achieved?
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Dec 26, 2010
Private Sub FontToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles FontToolStripMenuItem.Click Or Button1.Click
Is it possible to make a or?
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Feb 25, 2011
Private Sub Form1_Shown(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Shown
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Mar 19, 2010
it just gives me zero for my anwser.Can someone please make corrections?Public Class Form1 Private Sub xExitButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles xExitButton.Click
[Code]...
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Aug 23, 2011
On a client i have an anonymous list containing a multi-column primary key previously selected from the DB.Then i need to select all the records from the DB that equals the primary key list i have stored in the memory.[code]
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Mar 2, 2012
How i can import row from TABLE1 to TABLE2 without primary keyfield or adding correct value to primary key
i tried with two different codes, but result is same, it says: "In the column "Key"a constraint on the uniqueness.[code]...
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Jul 13, 2010
Why isn't this seemingly simple piece of code working?
Code: Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
For Each sp As String In My.Computer.Ports.SerialPortNames
ListBox1.Items.Add(sp)
Next
End Sub
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Jan 5, 2012
Is it possible to call a protected method via reflection. I am using this:
Me.GetType.InvokeMember(Stages(CurrentStage),
Reflection.BindingFlags.InvokeMethod,
Nothing,
Me,
Nothing)
Which always calls a method with no params or return. The idea is that the user of my object (transactional processing of business logic) inherits the base class adds in a load of private methods to fire. They then add these method names to a list in the order they would like them fired and the code above will take care of firing them.
It works fine with public methods but not with private or protected methods in the same class (Protected because I have some 'standard' pre built methods to add to the base class). Realistically I could make the methods public and be done with it but my inner nerd wont allow me to do so...
I am assuming this is a security feature. Is there a way to get around this or does anyone have any suggestions on how to proceed but keep my tasty, tasty visibility modifiers in tact?
(NOTE: ITS IN VB.NET but a C# Answer is fine if that is what you are comfortable with).
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Jul 23, 2010
if for example i have two private sub I declared a local variable on private sub a... is there a way that private sub b could use the variable created on private sub a? Im asking because im in a problem in my app were using global variable is not an option to make the long story short
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Feb 10, 2010
I have written a program which uses a SQL exception class and then use it show custom messages for the primary key violation. Also i want the primary key value that caused the violation. How can i get all the primary keys which generated the exception from the sqlexception object.[code]
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Aug 27, 2009
I searched on the forum / Internet for the solution how a PropetryInfo object (of a Public property) can reveal if it has a Private Protected Setter ... it was all in vain .... all help I found was about how to "Set" value of a public property having a Private Setter.I would like to know if I have a PropertyInfo object of a public property, how would I know if its Setter is Non Public?
I tried, in a exception handling block, where I did a GetValue of the PropertyInfo object and then called SetValue by setting the same value back... but to my surprise it worked well and didn error out.
[Code]...
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