C# - Check If A Class Is A New Instance Or Has At Least Once Property Populated Before Saving To Database
May 15, 2012
I thought this would be an easy one but I can't think of a good way to do it.User submits a webform. Based on submitted information I build three classes and assign their properties from received data:
UserInfo userInfo = new UserInfo();
UserAddress userAddress = new UserAddress();
UserEmployer userEmployer = new UserEmployer();
Based on submitted information some classes end up being populated with properties and some do not.
What's the best way to check whether userInfo class, for example, ended up with properties assigned ? I don't want to save a particular object to the database if it doesn't have any real properties assigned and all of them are set to either null or "".
I only want to save the objects that ended up with at least one real property assigned.ps. using NHibernate to save data to db
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Apr 10, 2011
Dim myObject As Something There I defined my variable myObject of type Something. But, as you can see, I am giving it no value yet. Sometime on runtime I want to check if myObject is holding a value or not. I tried this: If myObject <> Nothing Then But apparently I can't do such comparison.
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May 24, 2012
I have a checklistbox and I'm running the following
Public Sub ProcessCompanyAssociations()
Dim clientID As Integer
Dim fullname As String
Dim CheckedItems() As String = frmMain.clbCompanies.CheckedItems.Cast(Of String).ToArray
Dim UnCheckedItems() As String = frmMain.clbCompanies.Items.Cast(Of String).Except(CheckedItems).ToArray
[Code]...
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May 15, 2012
i defined a list of DataTables
Dim PreSubTables As New List(Of DataTable)()
Then I parse some source files and depending on the data, possibly none of the tables in the list PreSubTables2 might be populated, so it's just an empty list. Later on when i refer to the first table in the list , I get "index out of range error"
If (PreSubTables(0).Rows.Count > 0) Then ...
' just dealing with the first table: PreSubtables(0)
For ii = 0 To (PreSubTables(0).Rows.Count - 1)
[Code]....
I'm just trying to come up with a line that checks whether the(at least the first)Table in the list is populated, before I can print it out or do other things.
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Feb 16, 2010
In a combobox populated by a DataTable I am having two issues!The SelectedIndex property will not set 1. Either by integer 2. Or by FindString
[code]...
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Dec 28, 2011
i am using vb.net with asp.nethow am i going to check that this class has 10 people already if i continue adding the 11 one it should prompt me that the class is full once i click save button, i know is something like validating but not sure howi can first add a few student to class 2A and later on continue with adding to another class however, when i return to add more student into 2A and save, it should help to check like what i mention above i have this table call listOfStudent
listID class student registerNo
1 2A A 123
2 2A B 456
3 2B C 789
i have a aspx web page, i have a drop down list where i select the class
[code]...
when enter finish the first row of student data, user can click on the addNewRowButton to add a second row of student data and so on, then after all is done when the user click saveAllStudentDatabutton, it should check whether this class i selected from drop down list has already has 10 student if it does it prompt if it don't it will add in
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Feb 8, 2012
creating single instance form in MDI Application. How to check whether form's instance created or not?
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Jun 7, 2012
I want to created a nested class that can only be visible to and instantiated from the parent class.But I also want to be able to use an instance of the nested class through a public variable of the parent class.I tried making the nested class private, or making the nested class' constructor private, but it won't compile.Is it possible to do this in .NET?
[Code]...
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Dec 4, 2009
Visual Basic Project - Student Check In Form using an Access database backend This form needs to draw information from an Access database containg tables for STUDENT, INSTRUCTOR, and SECTION. These all need to have primary keys and ids. When (the user) clicks on the drop down box that displays all the sections:
{Table Tennis 1, Table Tennis 2, Table Tennis 3, Billiards 1, Billiards 2, Billiards 3}This should populate the listbox or datagrid from the STUDENT table with the Students that have the same SECTIONID as the SECTION selected in the drop down menu above.
After the Student list has been populated (the user) clicks on a student name in the listbox/datagrid and this inserts that student into the CHECKEDIN table that has a datagrid/listbox associated with it.
This is a great project to practice connecting a database to Visual Studio 2008 .net and playing with the data that has been pulled in. You could use SQL instead of Access.
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Jan 18, 2011
my proble is the following: I have a class MyClass and another class Modifier, which has a method ModifyMyClass(ByRef mc as MyClass) that receives a MyClass instance as ByRef parameter to modify it. A smell of the code is:
[Code]...
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Aug 19, 2009
I have a class in which some of the fields are also classes.I can put values in the "normal" properties, but in the others when o try to assign values it gives the: "Object reference not set to an instance of an object"But the code compiles fine.
dados_Defenicao = New ServiceReference1.draftClaimEntryDefinition
dados_Defenicao.arCode = "123"
dados_Defenicao.claimMarket.warrantyType = "w" - Here it gives the error
How can i fix this ?
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Aug 19, 2009
I have a class in which some of the fields are also classes.
I can put values in the "normal" properties, but in the others when o try to assign values it gives the: "Object reference not set to an instance of an object"
But the code compiles fine.
dados_Defenicao = New ServiceReference1.draftClaimEntryDefinition
dados_Defenicao.arCode = "123"
dados_Defenicao.claimMarket.warrantyType = "w" - Here it gives the error
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May 6, 2010
If you run this code you will see that the 500 PictureBoxes that are added ( this is easier to show than adding pixels as a pixel is only a single point ) fall mainly on the diagonal.With regard the RANDOM class, why should this be like this when the bounds of the instances are? >>
p.Location = New Point(x.Next(0, Me.Width + 1
), y.Next(0, Me.Height + 1 ))
as in this code.>>
[code].....-2138214fdeb4
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Apr 15, 2010
I'm using visual basic 2008 express I have 1 combobox which is populated from a coloum from my database, when I select a value from the combobox I wish to populate several textboxes with data from the row selected. I have created a dataset. How can I do this? Is there a tutorial I can read anywhere
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Feb 27, 2010
this is my code -
[Code]....
this shall populate the dropdownlist data, but in the value i need it to pick up the "ID" field from the stored proc. the stored proc sends two parameters, ID and Name. so i populate name, but how do i populate the id in value like this -
[Code]....
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May 18, 2010
I've createda vb.net class library where I've defined a number of small classes... nothing complicated, just working with strings, sending emails, etc.In another project, I reference the class library and I'm seemingly able to create an instance ofone of tclasses - intellisense shows me all of the plic properties, methods, etc... all looks perfect. No compile errors at all, nothing b gumdropsand lollipops.When I run the app I'm working on that references the class library, it fails at the point where I'm creating an instance of the class and gives me a vague exception, "System.TypeLoadException".
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Jan 20, 2012
Is there a way to define a class such that there can be only a single instance of that class?
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May 20, 2010
I need to create a new instance of a class that needs a member of the calling class. But i can't pass a reference to the calling class through the constructor.The solution i am looking for is something like this:
Public Class ChildClass
Public Sub New(args)
_MyMember = GetMemberFromCallingClass()
[code]....
I want this to work without having to manually pass any references or variables from the calling class to the new instance of ChildClass.
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Jun 11, 2012
I want to create a class that will "search" for something. Basically I load up the "search item" when the class is created and inside the class is logic to do the "search". The result of this logic will be more "searches" that I want to start. How can I have the logic in the class create another instance of the class itself?
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Jun 1, 2012
I have a very simple class that holds a few public properties - ID, Text, Colour, etc. and a Boolean called 'SelectedItem'. Just like the Checked property on RadioButtons, only one item can have its SelectedItem property set to True within a particular group. Note: there will be several separate groups (lists), each allowed to have only one item with SelectedItem = True.
My first thought was that I would probably just have to handle everything outside of the class, setting SelectedItem to False for every other item in a particular list when another item was selected. But that seems rather inelegant to me. So I've been trying to think of how this might be done within the class. For example: could I perhaps have a private string property called say "GroupName" - set in the New sub when adding a new instance of the class - and then use a private shared method to set every item's SelectedItem property to False, provided the item has the same GroupName as the newly selected item? I would have a go at doing this but I have no idea how to enumerate every instance of a class from within that class, or whether that's even possible. Is it? Or is there another (better) way to achieve my goal? Here is a cut-down version of what I've got so far:
Public Class ResourceItem
Public ID As Integer
Public Text As String[code]....
As can be seen: instead of instantiating a new ResourceItem and passing that as an argument to the manager's Add procedure, I'm simply passing the details of the new item and the procedure is creating the item from those. I don't know whether this is a good or bad idea - please advise - but I've done it because I couldn't figure out how to make the SelectedItem property only writeable by the manager, so I wanted to avoid having directly accessible objects that could have their SelectedItem property set to True without it deselecting all the other items in the same group. Of course that still leaves the possibility of setting a variable to one of the manager's list items and setting it from there, so I would still like to know how I could prevent that, if possible.
UPDATE: I didn't use the code above in the end, deciding instead to go with Cyborgx37's solution - which seems to work perfectly well for me despite the warnings about best practice. I also realised I would need to use the same class in another scenario where multiple items could be selected, so it was easy to add a Boolean property to the manager to enable that.
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Oct 1, 2010
I have a question on a datagrid object in vb.net 2008, that I what to be populated with certain values of a parameter from mssql database. The connection is made, the column header are loaded, but I what, when the form is loaded, to populate the datagrid only with certain values, doing a select commnad where id has a value given by me.What is the command to have this select done and display the values in the datagrid?
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Jun 6, 2011
I have an Asp web form (language is VB) that is used to update records in a SQL database. The form is populated with the record with many textboxes as well as dropdownlists. I have a textbox that is populated with a date from the record and is displayed with the date and the time. I would like change the format to only display the date as "mm-dd-yyy". In the code behind the date field is called from the database and put into the textbox via:
"MyDate.Text = dt.Rows(0)("MyDate").ToString()".
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Dec 17, 2010
I have a list view populated by a database. The columns for each record are First, Last and EMPID. When I look at the list view on the form at runtime, I can see some/all of the First name and then below that may be part of the Last and some ... periods and no EMPID. When I hover over the record, I can see the EMPID. Is there a way to have all of the information in the record visible in the list view?
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Dec 27, 2010
I'm working on a calculator for an online text based game, Cybernations. This game revolves around building your nation.I currently am using a class called Nation, this contains all the values for the nation such as infrastructure and land lvls. I want a way to save a nation as a file so that I can load it later and keep playing with it. I also want to be able to save multiple nations.
I'll need specifics on how to declare this in the program and where. I currently have a nation declared in my main form called ThisNation that is global. I think I can define ThisNation in the loading form as the selected file, but I'm not sure on how to do that. The actual file loading needs to be called from a button click in the loading form, then the program switches to the main form where you can actually do stuff.Where should I put the loading process, and how should I define ThisNation as the file?
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Aug 13, 2009
I have the following code:
Public Class MyColorsClass
'Constructors
Public Sub New()
'Empty Constructor
[code]....
However, if the empty constructor was called to instatiate this class then the colortype is not yet set. Therefore, if one accesses the 'IsColorCool' property it will always return 'False'. Now for the sake of this example, I must keep the empty constructor as part of the class.Now I could add some code in the 'IsPropertyCool' to check and see if a ColorType has been defined, and throw an exception if it has not been set, but I don't really want to do that.I also could always move the logic OUT of the property and into a method on the class called 'DefineIfColorIsCool' or something, and make the owness on the caller to make sure the method was called if they want to use the property 'IsColorCool'?
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Mar 9, 2009
rewriting a class I use for saving Treeview data to a XML file for use of saving ListView data I can't really figure out the rewrite, I'm stucked, unfortunately Listviews seems to be a big problem for me in general.
Option Strict On
''' <summary>
''' The TreeViewDataAccess class allows the nodes within a TreeView to be
''' persisted to xml for later retrevial.
''' </summary>
[Code]....
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May 8, 2009
After I have retrieved my data from my access database, I would like to insert text into one of the columns in a new row. Is this possible? Here's a snipit of my code I use to retrieve the data from access:
If con.State = ConnectionState.Closed Then con.Open()
sdr = cmd.ExecuteReader()
rtime = Now()
[Code]....
It's the rtotal_time value that I need to insert into a new row, in and cell, the datagrid.
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Apr 7, 2011
Supose a base class
Public Class airplane
Private var_num_seats As Integer
Private var_num_engines As Integer
[code]....
Obviously, I don't wish that the class Glider has the method "start_engines" neither the property "num_engines". Otherwise, other child classes may have. How can I supress these property and method in child class, not just ignoring (if I can)?
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Sep 29, 2011
I have procedure (Import) that calls a for a new instance of frmImportData. I also have a class name clsBatch that has a data table property called prpParametersTable.For some reason, I get an error (indicated below with ERROR>>>) when trying to assign prpParameterTable to cv_dtImport2. The error states "Object reference not set to an instance of an object.". Why does this error not happen when I assign dtBP to cv_dtImport1? Both cv_dtImport1 and cv_dtImport2 are equal to Nothing and in my Import procedure dtBP = prpParametersTable.
Public Sub Import(ByVal clsB As clsBatch)
Try
Me.cv_clsB = clsB
[code]....
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Nov 14, 2009
I have three class files, accounts.vb and transactions.vb in addition to my form.vb. I am unable to retrieve a member variable from on class from inside the other. When the combobox index changes, the program loads the correct account (checking or saving) from two different sequential files. I don't think I have the calcBalance procedure in the correct class file. And that is what I am having trouble with. Accessing it to display it. [Code]
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