I am having trouble getting inheritance to work with the VB 2008 Express entity classes. I am a beginner with VB.Net and self-taught in VB6.0.I am able to pull data from an SQL Server data base into my application using the O/R designer. The data can be successfully queried using LINQ to SQL, either returning a single record, or multiple records or an entire table as a collection of the enty class type (so the problem is not with LINQ queries).
I've been wondering if there is anyway to extend a sub of a base class in a derived class or subclass. To date, the only thing I've been able to find is overrides and overloads functions, but to my understanding these functions just ignore your base class's sub and just allows you to run the new one with the same name.
What I want to be able to do is:
CODE:
I'm not sure whether this is possible, or if I'd simply either make a new sub in my derived class that first ran the base's class sub or whether I'd override the base class and then copy and paste the old code.
I am using the O/R Designer to create entity classes in VB 2010. I am observing different results for different database tables that I can't explain and more importantly, can't replicate the results that I want.Using server explorer, I have dragged a number of tables on the O/R designer surface, thereby creating the entity classes.
I have saved the project and can access the various entity classes in my project code. I first noticed a difference when changes made to object instances from some tables/entity classes appeared to persist while changes made to object instances from other tables/entity classes did not persist. These object instances are created, accessed, and changed using the exact same code patterns except for the object, class and table names.
I have been looking to see if there are any differences between the way in which the entity classes are treated, either in my code, in server explorer, or in the O/R Designer. I cannot find any. The properties of the entity classes indicate that all of the classes use the runtime methods for insert, delete and update. As far as I am aware, I have not knowingly made changes to these methods.
The ONLY difference that I find is in the file NameofClass.designer.vb. This is an automatically generated document. The partial class of those objects that appear to persist changes contains different code from that of other partial classes where changes to objects do not persist.In the declarations section of this partial class, the following lines appear:
<Global.System.Data.Linq.Mapping.TableAttribute(Name:="dbo.OrderofBattle")> _ Partial Public Class OrderofBattle Implements System.ComponentModel.INotifyPropertyChanging, System.ComponentModel.INotifyPropertyChanged
[code]....
If I am right then I want to enable persistence in my other classes by causing this additional code to be generated for them. But how? why the code for this one class hase been generated differently than for all the others (actually it is this way for 2 out of about 15 classes). What setting or or selection do I have to make to enable this code to be created for my other entity classes during the automated process?
Background:I have a base class and several inherited derived classes. The derived classes don't always need to have the same properties. If any properties are shared among the derived classes, those properties would live at the base class level ('Contents', for example).Similarly, GoodDocument below has 'GoodThings' but would not want/need to have 'BadThings'.I want to treat instances of both 'GoodDocument' and 'BadDocument' as type 'Document'
public mustinherit class Document public property Contents as string public sub new()...
I am cleaning up some code and I have multiple classes that are 99% exactly the same. So my understanding is that my options are...
1. Create a class and all other classes inherit from it and modify it a bit
2. Create an abstract class and all classes inherit from it and modify a bit ** I took this route
3. Create an interface and all classes Implement that interface.
Here is my 'original' class below (the one that all of them look 99% identical). This class is used in an arraylist so I have a listing of all my images from a folder I have searched.
I seem to be having a problem with controls that I am creating as new classes (not UserControls) inheriting from an existing system control. Everything seems ok while I create the control code, through to the compile (which is successful and adds the control to the toolbox) and dragging the control from the toolbox to the GUI surface. However, when I then debug or compile the project, I get a message such
I'm using a 3rd party tool to generate my model including code classes for the MS Entity framework. What I wanna do is etablish a real layer application. I'm speaking of the layers:
Presentation Business Data
If I'm not wrong the generated classes represent the data layer. My question is if I should wrap this classes up for my business layer or not. In some way these generated classes already represents the logic of my application as it was derived from my database. But is this enough?
I definitely wanna use LINQ as well which works pretty good with the generated classes alone.
I'm looking forward to any comments.BTW: It's going to be a ASP.NET web application. I have used the projetc type "class library" for the data layer. The web application will use this DLL.
I am trying to build a survey engine from an existing database design which is like this.
[Code]...
The line Order By Key.RecordOrder throws a null reference exception and I can understand why. Can someone advise on how to resolve this by just modifying this one query? I am fairly new to LINQ and the necessity to write this project
I want to update an entity without loading the entity from the database first. I've accomplished this but only by knowing all of the entities properties and then using the "attachto" method. My issues is i don't want my app to need to remember all of the properties. Example:
Entity Splitting: one class, two or more tables.Here is how it is done in C#, but I need to get it working in vb.net.One more thing: the class name and table columns do not match, so I have to be able to map that out, too.I have to get this to work this way because the place I'm working at right now is a vb.net only shop and the database schema is fubar, but they have so much (millions) of lines of code done directly against the database in both asp classic, vb.net, AND asp.net webforms that changing the schema right now is not realistically possible.
I have a base object, with a event that can be triggered by multiple methods.Then I created a child object that inherits that base object. I want to be able to trigger that event in the new object; but I can't use RaiseEvent to raise a base-object's event.To get around this, I created a small method in the base object that takes the argument for the event and I just use it to trigger the event. Is this the proper way to handle this situation? Similarly, I could Shadow the event with a duplicate one in the child object.Is there a standard way to handle events across inheritance?
I've not played with inheritance myself much as I've never really had a need to, but now I have a situation which to me seems the ideal time to learn. I'll explain:
This is a WPF application but that shouldnt make any difference to this question. Basically, I have asearch window that retrieves data from a database - I want this one search window to be able to retrieve any item (business object might be a better word than item) from the database and display the relevant data, rather than having a separate window for each 'type' of item in my program. So I have got 3 classes at the moment, ComputerAudit, ConnectionAudit, and SoftwareAudit and I want my one search window to be able to display any of these items in the listbox. Obviously there would only be one type of item displayed at once, so there wouldnt be a computeraudit item and a connectionaudit item displayed in the list at the same time, but there could be several computeraudit items displayed.
So I thought I could create a base class just named Audit and have those 3 classes I mentioned inherit from that, then I can specify the arguments to methods I am using as just being of type Audit (rather than using a specific type like ComputerAudit or SoftwareAudit) because then I should be able to pass around any of these items which inherit from Audit right? Well that doesnt seem to be the case so I'm wondering if I have misunderstood inheritance.
The problem I'm having specifically is that I have some methods which need to be able to accept any of my Audit subclasses but if I specify a generic List(Of Audit) then it wont let me pass in a List(Of ComputerAudit) for example. Is this because I'm using a List or am I just doing something fundamentally wrong?
EDIT: Found this page which confirms my suspicions that this is more to do with the List than general inheritance:[URL]...
I am trying to jump from ASP Classic to asp.net. I have followed tutorials to get Entity Framework and LINQ to connect to my test database, but I am having difficulties figuring out ExecuteQuery(). I believe the problem is that I need an "entity class" for my database, but I can't figure out how to do it. Here is my simple code:
Dim db as New TestModel.TestEntity Dim results AS IEnumerable(OF ???) = db.ExecuteQuery(Of ???)("Select * from Table1")
From the microsoft example site, they use an entity class called Customers, but I don't understand what that means.
I am trying to create a generic typed class, but am running into a problem. Here is my basic class definition:
public class QueueObject<T> where T : System.ServiceModel.DomainServices.Client.Entity { public string LoadingMessage { get; set; } public System.ServiceModel.DomainServices.Client.EntityQuery<T> Query { get; set; } }
I am trying to add instances of this class to a queue
This doesn't work. I get an error saying that QueueObject cannont be converted to QueueObject. I don't understand because MyEntity inherits from Entity.
Public Class QueueObject(Of T As System.ServiceModel.DomainServices.Client.Entity) Public Property LoadingMessage As String Public Property Query As System.ServiceModel.DomainServices.Client.EntityQuery(Of T) End Class
I have two custom objects.On of them inherits the other one, appends few more properties and methods, ovverides some other.When I try to cast the Parnet Object to Child I receive an error that it could`nt be done.
If I declare and instantiate an instance of class B within class A, how do I make instances of class A member objects/variables accessible from class B?
In my application i will use a customized datagridview for all the application, so instead of adding the normal datagridview and changing the properties, i created an user control and changed the inherited to datagridview... This have a problem i can't use the drag and drop...
I have two classes, one nested in the other. [code]Neither "Name" or "ID" are unique between operations and records.I wish to construct a dictionary using LINQ = Dictionary(Of String, Of List(Of Integer), whereby the keys are uniqe examples of Names in my collection and the values are the collective set of distinct IDs that are associated with those names.
I have a application based on the entity framework. I have extended one of the classes (Quotes) wit 'partial class', and within that i've created a method that is completely independant of any database properties. For simplicity lets say it looks like this:
[code]...
All is good, except i need to bind this to my a textbox in my UI and have the textbox update automatically when the property is changed (like a dependency property). This is proving problamatic, I've tried both invoking the onPropertyChanged sub that the entity framwork exposes and implementing intoifychanged. Both cause errors.
How can I structure my classes so that the user interfaces though a single class while the supporting classes are hidden from their view? I think its best understood in an example:
Public Class MyInterface Public Economic as EconomicClass Public Sub New() MyBase.New()
[code].....
So you might ask why am I even separating them? It's strictly for others who will be working with this interface. I need to funnel them though a logical structure:
This way everything is already handled for them in the background and they only need to run the method they need. I don't know if I can have it both ways in VB.NET.
If I have something like this within a sub/function:Dim a as new myclass...Does this leave a memory leak if I am constantly calling this function creating new instances of this class? Do I have to destroy it or something when I am done using it?
I have a Tcp Client which I created on an application form but now I would like to create a class for it.
My prob is that when I check for any incoming data, I used to start a new thread. When this new thread finds any incoming data, I call a sub which invokes the form and everything works smooth.
This is what I am talking about,[code...]
How would I be able to do the same from a class? Or I dont have to create a separate thread when using classes?
I am curious as to the proper technique to use SQL Server's AppRole with a LINQ to SQL Class. I understand I have to establish the intial connection with no connection pooling. However, do I simply call the SQL stored procedure sp_setapprole using standard LINQ before executing any of my methods that interact with the database, or is there a better way to enable and use AppRole within the LINQ to SQL class?
I'm running into is some of the namespaces aren't being recognized. After searching the internet it seems I am supposed to have more than just System.Management.Instrumentation available to Import/Reference.However, that is all I can access.I need System. Management. ConnectionOptions and a few others, but don't know how to get these.Do I need to install the WMI SDK, or maybe the WMI Win32 Classes?
