How To Create A Dataset-like Class
May 18, 2011
I've been struggling with this for a while, so I finally decided to ask the question rather than try to figure it out myself.Generally, what I want is a more robust Dataset. I have to do a large quantity of hiarchical calculations, doing a wide variety of calculations.I used datasets for similar situations in the past, but there are some restrictions with datasets that I need to have, such as:Datasets are restrictive in their calculation methods, such as having no method for doing powers calculationsDatacolumns are restrictive in the types they can be, at least in the designer. I need members of this class to be of custom types.
I like the way expressions in datacolumns will calculate only when the dependent columns change. If I build a custom class that recalculates every time the value is accessed, it takes an unacceptable amount of time to recalculate all of the fields. I'd likethe class to only recalculate the value of the field when it needs to.
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Aug 7, 2009
This is my vb6 programme for creating recordset in a module. and call it in class
and form
[Code]...
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Jun 28, 2009
I created a SQL database using the migration tool.I am converting my access forms to VB.net (VS2008).I am wondering if I create a single dataset in studio to the database or do I create a dataset for each form (query)? I am trying to determine what the best solution is. Many of my forms have drop downs that are populated using queries from tables.
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Oct 9, 2009
does VBasic allow a MS Access Database DataSet create a Stored Procedure or will it only allow SQL Database DataSet create SP...
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Apr 17, 2009
I have produced an application which works with datasets but I now wish to provide the user the ability to add and admend records within the database.But i wish to do this in a seperate form.My current dataset instanciates classes onLoad.Should i try passing the Dataset to the new form class? although I have the problem where by when i pass the dataset to the form class using code below i get this problem:[code]Should i just create a create a new connection to the database and produce a new dataset for this form? or is there a better way to do this?
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Oct 1, 2008
I've been creating short test apps repeatedly to try to understand some of the concepts in VB.NET.For the most part it has been illuminating.I read Bucky's .NET knowlegebase tutorial on passing objects as parameters to newly created forms. He shows how to create a new class that inherits from the base form class and define a New() method with parameters Extending the concept I thought about doing the same thing with a form that was created at design-time (In this case Form2).
[Code]...
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Apr 27, 2011
I want to read a number of items from a file and then associate each of those items with a new button at run-time, so that when the user clicks one of the buttons I can display some information about that item.Can I use a LIST to manage these buttons and items? Can I create a new class and have each list item of that class, such as 'btnID', 'btnText', etc... ?
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Feb 23, 2011
Can we create objects of a C# class from a VB.NET class and vice versa?
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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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Nov 28, 2010
I want to create a class is it where I can do...
[code]...
How do I do this? Do i create a class and create a instance of CarData? but how do I add Color and Year etc to it?
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Aug 5, 2009
I have a textbox which is bounded to the typed dataset. If the user in the textbox &hit keydown, it should allow only numeric values with 2 decimal points and also it should not allow more than one "."(dot). I found many but all thats are using textbox event
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May 19, 2010
I have got problem when using the SQLCommandBuilder class. For me it throws an error saying that the select statement does not return any primary columns.... Which is weird becouse i am sure it does since the select statement is "SELECT * FROM MyTable" I am prety sure that selects everything including the primary column which is set to primary , realy i checked and doublechecked.
Secondly i tried to manually set the column(0) as primary by setting it's property bu no such luck of making it work.
I have these two functions in a class that i instanciate an object from in the main program:
Code:
Public Function GetDB(ByVal DBName As String) As Data.DataSetDim SQLAdapter As SqlClient.SqlDataAdapter = Nothing
Try_SQLdataSet = Nothing
[CODE]...
This Functtion fills the dataset and returns it to my main program where i do lovely stuff with it. (Just as a side note this is a SCADA system and i always need the entire DB which is never bigger then just a few ( 6 ) entries so i must go for "*" ^^). Good part is, this works like a charm, i love it. Now i need to reset a few status bits etc and i assume with the update command. And that is where my joy starts to get stomped on a bit.... The code:
Code:
Public Function SetDB(ByVal dataTable As Data.DataSet, ByVal DBName As String) As BooleanDim SQLAdapter As SqlClient.SqlDataAdapter = Nothing
Dim SQLCommandBuilder As SqlClient.SqlCommandBuilder
[CODE]...
Now this would have been a great and small sollution to updating datasets with the server but obviously it doesn't work. There is that pesky error about my table having no primary key and I know it's lying it just want to annoy me :P. But seriously I am puzzeld why that error wont go away and i have exhausted all the tutorials i can find on this.
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Nov 1, 2011
I was using the following code within a class and creating an instance of that class from within my main form (Main.vb):Dim count As Integer = Main.DbDataSet.Accounts.CountThis was returning the count of accounts within my database.After changing the code so that I could run this in a background thread to save locking up the program, as more data is processed after this point, the count was returning 0 each time.
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Apr 12, 2011
I have written some functions that I have in a module. In one of the functions I would like to update a table that is in a dataset. I would like to do this with this function and not from a form class where the table could be bound. I need to call the function from various places in the application.
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Mar 25, 2009
I am compressing a dataset converted to XML using the GZipStream class added in 2.0. There are a few things bothering me about this. Here's the code I am using to decompress the XML file:
Using inFile As New System.IO.FileStream(flnm, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read)
Dim zStrm As New System.IO.Compression.GZipStream(inFile, IO.Compression.CompressionMode.Decompress)
Dim buff(999) As Byte
[CODE]...
This seems inordinately awkward, as I am taking the stream, reading it out into byte buffers, then writing those byte buffers to a memory stream that is then passed to the dataset.ReadXml() method. The reason for this seems to have to do with what is happening in the line colored red. That line is adding a closing > onto the end of the stream. Without that, ReadXml complains about an unclosed dataset. I found out that the > was missing by writing the stream into a string and pasting the string into WordPad. Without that missing >, it appears that I wouldn't need to be using that memory stream at all, and could simply pass in the GZipStream to ReadXML, but as far as I can tell, it's impossible to look at the GZipStream to be sure that the > is not there, and it may be impossible to add it (I haven't tried).
So why is the > missing? Here's the code used to create the file that is being read into the filestream in the above
VB Using ms As New System.IO.FileStream(flnm, IO.FileMode.OpenOrCreate, IO.FileAccess.Write, IO.FileShare.Write)
Dim zStrm As New System.IO.Compression.GZipStream(ms, IO.Compression.CompressionMode.Compress)
ds.WriteXml(zStrm, XmlWriteMode.WriteSchema)
End Using
The real kicker to all of this is that while I was dissecting the first chunk of code, I added a line to check for cnt<1000. My intention was to see the last buffer that was being written into the memory stream to see whether the final > was actually there, or not. To my surprise, I reached the cnt<1000 twice. That means that one read did not read a full 1000 bytes, but read only 675. The next three or four reads were a full 1000 bytes, then the final read was just a few hundred bytes. It is my understanding that Read will return a full buffer if there are that many bytes left to read, and there were, so why did it return only a partial buffer? That suggests that there might be a hole in my XML, though with a half meg file, it's a bit much to read through it looking for something missing. However, the XML that was returned was turned into a dataset that I then merged into some existing data using code that has been working with uncompressed XML files, and I got an error that I should never have received. That may indicate that the XML was, in fact, missing something, though I will have to study the matter further to figure out whether or not that is the case. My major question has to do with the missing '>' at the very end of the file.
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Jul 21, 2011
I'm working on a helper class that will make things easier for me when connecting to and viewing a crystal report.Now I need to create a Property called DataSource. Crystal has a SetDataSource method that has 4 overloads/constructors(not sure what the right term is)1 accepts a System.Collections.Ienumerable, the 2nd accepts a Dataset, the 3rd a DataTable, and the 4th a DataReader.Now I want my property to be able to accept all those. So what Type must my property be.If I can just have DataSet and DataTable for now it would be fine, as I work with those mostly Public Property DataSource as?
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Sep 10, 2008
I'm in the process of trying to create a class that will allow me to create windows shortcut; Im using the following PDF file that gives me the shortcut file structure.
Ive been able to successfully load a shortcut file and parse its Lnk File Structure but now Im on the Shell Item ID List structure but I cannot find the Structure of the ITEMIDLIST anywhere
Furthermore I know I could use the Windows script object, but this is a dependency Im trying to avoid if I can, hence writing my own Shortcut class.
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Feb 27, 2011
I'm try to create a class has been create by main class only by protect sub New but how do I create it ?
Public MustInherit Class Rune
Protected MustOverride Function Create() As Rune
Public Shared Function Factory(Of T As Rune)() As T
'I can't use "T As {Rune, New}" because Sub New isn't Public
'Return (New T).Create
End Function
End Class
[Code]...
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Mar 15, 2009
I have loaded XML doc into a dataset (see below). That went ok. So now I can put the DS in a grid and change it.However, after changing the DS I want to export it back to a XML doc. That only succeeds partially.I am getting a XML doc, but it's not like the original (see below). And I want it to be exactly like the original.Maybe you brilliant guys can help me out The original XML code (I tried both with and without the Schema):
[Code]...
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Jan 27, 2010
I am instantiating a form object in my code behind the dataset just to access some form level variables and to occasionally set a label in the navigator bar. Recently in the b2 Team version of VS2010 there are some strange errors thrown in the immediate window and then I'm tossed out of debug mode and back into the IDE. This code has been operating for some time in this project without this behavior. A team member has just reproduced the behavior in his development machine also.The error that starts the shutdown of the debug instance is this: Control accessed from a thread other than the thread it was created on.
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Sep 19, 2009
In VB2005, I had create a DataSet, like EmployeeDataSet.xsd, how to put it into a form?
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Dec 27, 2010
I want to create a dataset that I can access from any form. I already created the tables and columns using the dataset designer. I read that I can declare the dataset as public in a module, but when I try to access a table I have to put the name of the module in front otherwise I get a "Reference to a non-shared member requires an object reference" error. When I declare a variable as public in a module I never have to specify the name of the module to access the variable, so why do I need to do it for a dataset? The code in my module is:
[Code]....
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Jan 13, 2009
I have the following code which output data in an XML format and updates a row in the dataset to say its been exported.[code]...
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Jun 5, 2011
i am trying to create a dataset for use with crystal reports. i have a dataset called dataset.xsd with two tables BatchHeader and BatchDetail these have a relationship of BatchID on both tables.(see picture1)
[Code]...
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Jan 2, 2010
How to create a dataview from a datatable?
What is the basic use of the created dataview?
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Sep 3, 2009
I want to create an enterprise wide dataset so that my function will call this same dataset from any of the webpage. I've created shared code in the App_Code folder. In it, there's are dataset properties. Will the pages extract info from these dataset properties each time I call the shared program or will create new property for each page.I'm trying to emulate an Enterprise Java Bean type of coding.
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Jun 10, 2009
I have a datagridview that was bound using the wizard and all the column created that way. So I haven't done any code to bind the datagridview. It will pull the data from the database and dataset just fine. My problem is when I create a new row it won't update the dataset or database. I have tried different ways that I thought it would work in the code and still haven't found a usable way to do it yet. Or if I need to do all my binding and columns through code give me an idea where to start if I have to go that route. This is my first experiences with Datagridview. I normally use comboboxes and textboxes to write to a dataset and database which all work very well.
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Aug 4, 2011
I have an XML file that has a basic hierarchical structure about horse racing. It has a summary of the tracks, some data about each track, then a list of all the races at each track racing that day. So lets say there are 10 tracks, and for each track there are 8 races. This is a snapshot of the data....
HTML
-<Meetings xmlns="" Jurisdiction="VIC">
-<Summary MID="MR_20110801">
<VenueName>ECHUCA (VIC)</VenueName>
<Type>R</Type>
<Events>10</Events>
<Track>DEAD </Track>
[Code] ......
I have written the code to pull down the data into a data store, but I dont know the BEST way to put the data into a set of tables. My first thought was to traverse the nodes and add rows into tables but I figure there must be a native VB process that reads the xml and puts it into the the appropriate table. How to code up the process for getting the data into a set of tables that match the xml. So lets say I have a Summary table, I would like all the data about each track to go into that table. Then I would have a Races table and have the data for each race go into that. What I have done already is import the xml into Access to create the tables (which was a breeze!) and then link that data source to my project. So I have the tables already built.
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Aug 25, 2009
i have a form which accepts inputs from the user. I want to create a crystal report ( not from the database but from the form ) and to create a crystal report, i need to create a dataset. i dont know how to create dataset from the form's input
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Jan 13, 2009
I am trying to create a combo box that would display data from a dataset, and also a 'Please Select' as the first item. I have written the following code which derives from a combo box and it works fine in visual studio 2003 but in 2008 would not display the comboboxtext (which is 'Please select').
Public Class DoubleDataSourceCombo
Inherits ComboBox
Dim myDataTable As DataTable
[Code]....
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