Creating A Data Layer - Prototype An Application With A data Layer?
Jul 26, 2009
I am trying to prototype an application with a data layer on my computer at home using Visual Basic 2008 express edition with SQL Server Compact 3.5. My production situation at work is SQL Server 2000 and I am using Visual Basic 2005 professional for development.I am trying to write the code to create a seperate data layer. Here is my code. First the data layer:
Imports
System.Data
Imports[code].....
My Problem is that the data does not show up in the text boxes.
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Feb 7, 2011
I am generally following this tutorial, the main differences being I'm using 2008 R2 Express and Windows Forms, he is using 2005 & ASP.NET Web Site:'m building a minimalist Windows Form project for learning purposes. So I'm using a 1-table database with 2 columns, ContactID & Name. I added a dataset file, 'ContactsDataSet.xsd' to my project and added a single minimalist table adapter with just a fill() & getdata() method.Then I added a DataGridView control and connected it to the ContactsDataSet to confirm it was working and that worked fine. I ran it and it filled up with data as expected. Everything up to this point was auto-generated code.
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Jun 21, 2010
I'm creating my Data Access Layer and I want to return my object but not all the fields so this is the code i'm using
CODE:
I then call this method in the Business Logic Layer
CODE:
lastly I try to call in in my user interface and bind it to a DataGridView
CODE:
But I keep getting this error: Unable to cast object of type 'System.Data.Linq.DataQuery`1[VB$AnonymousType_0`3[System.String,System.String,System.String]]' to type 'System.Collections.Generic.IEnumerable`1[PP_DAL.DCProposal]'.
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Dec 4, 2009
I am a fairly rookie programmer who is trying to learn the basics of n-layered architecture (DAL, BLL, UI). The application I am programming is a single tier, 3-layer application written in VB.NET (.Net 3.5). Layers as follows:
DAL
BLL
UI
COMMON - contains DTO's right now.
I am having trouble determining what to pass between my BLL and UI. My instinct tells me that I should only pass data to the UI, and not the full business object from the BLL. Consider two scenarios:
1) Pass the BO directly from BLL to UI. This exposes BO methods and allows the UI direct access to the BO, which seems bad.
2) Pass only the pertinent data from the BO to the UI. For instance, a customer has a Name and Address. This data is really what we want to show/edit in the UI, so we would only return that data to the UI instead of the full BO. The UI would then call to the BLL to update a specific BO.
I am inclined to use #2, but I don't know the best way to implement it. The way I have it programmed now, if I only return data from the BLL, all references to my BO's will be lost and the GC will claim them. Based on this, I have some questions:
1) Should I keep business objects alive between calls to the BLL? The alternative is to re-create them every time I pass data through the BLL, which seems wrong.
2) What is the best way to keep a BO alive in a single tier architecture (how to hold a reference if we dont pass it to the UI?)
3) How do n-tier applications do this? Do they keep the BO's alive in the BLL and wait for an update from the UI? Doesn't this require a lot of "book keeping" in the BLL to make sure BO's are released when they are no longer needed?
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Nov 30, 2010
I am working in VB.NET defining my own classes. I have 5 classes, Policy, Coverage, CoverageCollection, Layer, and LayerCollection. Policy has a bunch of data items, one of which is of type CoverageCollection. Coverage has a bunch of data items, one of which is of type LayerCollection.
Policy
private id as Long
private name as String[code].....
Then I do like "dim p as Policy". So, iIn order to get to properties on a Layer, I reference it like p.cov(0).lyr(0).face. What I am trying to do is add a readonly property to Layer that is calculated using some Layer information but also using something from Coverage (or even Policy). I can take this in as a parameter to the property, but I think there should be a way to get at Coverage/Policy information since I am "under" it already. Is there a way to do this?
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Jul 25, 2011
I've never used a List(Of) before and I'm not sure how to pass it to the Data Layer of my application. The ColResCategory is a property within the Business Layer (See below) and it needs to be passed to the Data Layer. ReplaceResCategory (See 2nd Code view) is another class file within my Business Layer and the ColResCategory references it.
Public Property ColResCategory() As List(Of ReplaceResCategory)
Get
If IsNothing(mColResCategory) Then
mColResCategory = New List(Of ReplaceResCategory)
End If
Return mColResCategory
[Code] .....
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Feb 19, 2011
I'm creating a Data Layer for a Web Application and in one of my functions, I need to pass in a Structure full of Customer info. This Data Layer is essentially a DLL. My problem is that I'm not sure how to do this.Below is my code and what I want to do.
[Code]...
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May 22, 2009
I am putting some heavy though into re-writing the data access layer in my software(If you could even call it that). This was really my first project that uses, and things were done in an improper manner. In my project all of the data that is being pulled is being stored in an arraylist. some of the data is converted from the arraylist into an typed object, before being put backinto an arraylist.Also, there is no central set of queries in the application.This means that some queries are copy and pasted, which I want to eliminate as well.This application has some custom objects that are very standard to the application, and some queries that are very standard to those objects.
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Feb 20, 2009
I am implementing a Data Access Layer (DAL), which is basically a set of classes with (VB.NET) Shared functions to actually execute the database (CRUD) calls. I am trying to figure out the best place to place the calls to the DAL within the class hierarchy. Let me give an example.Suppose I have a class Customer, with only standard ID, Name, Address1, etc. properties and maybe an overridden ToString function or so. I also have a DAL class with Shared methods, such as:[code]Would this be "cleaner" OOP? Or is it acceptable practice to let the presentation call the Dal, passing the business objects like my previous example:[code]
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Mar 23, 2010
Im experiencing some problems while attempting to read a connection string from an App.config file in my Data Access Layer.I added the App.Config to the DAL Class Library, and added my connection string to the connectionStrings section but when I try to read it from my DAL its Returing Nothing.
[Code]...
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May 28, 2009
Need a SQL Server "SQLClient" (VB) Data Layer Class?
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Oct 1, 2009
One of the time consuming factors of writing the DAL is adding and assigning paramters of teh stored procedure if ther are more than 10 parameters and must link more than 3 tables this process will take a horrible amount of time..
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Mar 1, 2010
Im writing a data access layer for my application.There are several functions that need to return a list of items like Employee Name, and EmployeeID so it can be bound to a dropdownlist.What would be the proper datatype to return, a Dictionary?The lists only contain 2 columns, a name and id.
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Feb 27, 2009
We have data that's updated nightly in a database residing in the same instance as my app's database. So to save on database calls, I want to cache this static-for-the-day data into a List(Of MyObject). From a theory point of view, should this cached List(Of ) be cached in the presentation layer code, via a global variable? Should it be in a global variable in the .DLL?I'm thinking in the .DLL, because I created a service layer, which is exposed publicly to the GUI and makes calls to the data access layer inside the .DLL:
Public Shared Function Search(ByVal criteria As Core.Other.Customer) As List(Of Core.Other.Customer)
' TODO: Check the customer cache to see if it has been populated yet. If not, populate it.
If 1 = 1 Then
[code]....
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Mar 14, 2012
If you want to go to [url]... there is a tutorial about Luna, a vb.net code generator for data Layer of application
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Jan 15, 2010
I typically dont create interfaces unless i have to, however in my current application i have to create interfaces in the Data access layer. I'm a in a minor confusion that hwo do i create those interfaces more how to implement them: the following code might make things clear:I have the following class and interface in the data access namespace
[code="vb"]Imports ConsoleApplication8.BusinessLayerImports ConsoleApplication8.DataAccessLayerImports System.DataImports System
Namespace DataAccessLayer
Public Class CountryGateway Implements ICountryGateway
[code]....
1. Is this way implement the interface in the data access layer? (in this case the class CountryGateway access the database.)
2. I have been told that we should create interfaces than abstract classes espcially in the data access layer, is there a particular reason for this?
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Oct 1, 2010
Our application uses a custom DataAccessLayer class almost exclusively, and within that we do use Data Access Application Block (currently version 2). We are getting the infamous "GetOrdinal" error sporadically. We are not using out-of-method connections. We are using DAAB version 2. Below is a typical example of our DAL methods:
Public Function MyDALMethod(ByVal Param1 As Integer, ByVal Param2 As Integer) As System.Data.IDataReader
Dim db As Database = DatabaseFactory.CreateDatabase()
[Code].....
My main question is should these DAL references be disposed somehow? It's a custom class written in VB.NET, so it doesn't implement IDisposable so I'm not sure if there's anything to be done or not, but we do have errors and issues (like the GetOrdinal problem) which seem to be load-related, and I'm wondering if this is part of the problem.
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Aug 27, 2009
I am using Oracle 11g client, with ODP.NET. I am trying to add conditional Transaction handling.
Dim ds As New DataSet()
Dim txn As OracleTransaction
Dim _beginTransaction as Bolean = true
Using conn As New OracleConnection(ConnString)
[Code]...
How do I fix txn being nothing / null? The error is: Variable 'txn' is used before it has been assigned a value. A null reference exception could result at runtime. Edit: to RichardOD for pointing out that you can not explicitly declare that a transaction cannot be opend up on stored procedures via ODP.NET. I have verified that this is an issue. BUT We still haven't figured out why the error is occuring. I understand that txn is initially given a value w/in an if statement, but being defined outside of the try/catch block should make that irrelevant.... right? Or is that bad coding?
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May 28, 2009
What are good things to check for, with respect to error-handling, when you are dealing with the data-access-layer? For example, let's assume I have this function..
Public Function UserExists(ByVal userName As String) As DataTable
Dim dt As Object = Nothing
Dim arSqlParameters(0) As SqlParameter
[code]....
How would you go about ensuring that your code elegantly handles anything unexpected in a situation like this?
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Jun 22, 2012
I used to build data layer by using Classes, however someone suggest to use Strongly Typed DataSets because it's faster in development. The data layer that I'm going to build should support multi DBMS(Oracle,MSSQL, MySQL..)
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Aug 17, 2009
I used to build data layer by using Classes, however someone suggest to use Strongly Typed DataSets because it's faster in development. The data layer that I'm going to build should support multi DBMS(Oracle,MSSQL, MySQL..).
how is better build it by using Strongly Typed DataSets or by using Classes?
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Mar 14, 2010
I would like to build a base class for my SQL Data Access Layer. I have most of it based out, but have a question about how to handle errors within the base class. I have a method for ExecuteNonQuery, ExecuteReader, ect...
[Code]...
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Aug 25, 2009
IN my daat access layer, the stored procedure returns value of the format "CCT1". But i need to format that value to "CCT00001". Should i do this formatting in the data access layer or in the business layer?
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Mar 4, 2011
I've always used this approach while implementing data layer DLL for web application:
1) put datasets into the dll project
2) use a helper class with a method like this:
public shared sub settCnnStr(strconnhere as string)
My.Settings.Item("connectionString") = strconnhere
end sub
3) when I need to use the dll I call a method like this (usually into global.asax):
xxxxxxx.helper.setCnnStr("yyyyyyyyyyyyyy")
This method always worked for me nicely but I'd like to know if this method could have serious drawback or if there's a better solution.
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Feb 3, 2012
I'm trying to learn how to write a data layer class to read in information and populate combo boxes, etc.
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Feb 24, 2011
Ok, so I was playing around with Ninject, a "Service Layer" and a "Repository Layer".I built a simple console application to to play around, this is what I came up with:
Imports Ninject
Module Module1
Sub Main()
Dim Kernel As IKernel = New StandardKernel(New CustomerModule)
Dim Service = Kernel.Get(Of CustomerService)()
Console.WriteLine(Service.GetCustomerByID(1).Name)
Console.Read()
[Code]...
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May 15, 2009
I'm looking into adding some unit tests for some classes in my data access layer and I'm looking at an update routine that has no return value.It simply updates a row based on the id you provide at whichever column name you provide.Inside of this method, we collect the parameters and pass them to a helper routine which calls the stored procedure to update the table.Is there a recommended approach for how to do unit testing in such a scenario?
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Aug 12, 2010
What i am looking is how to create a layer between the application and database? I need to create an xml files where the application will fetches the data and updates the data into local cache. Later from the xml files the data has to be transferred to database. Here the application need to work even when the application is in offline and database is not been connected.
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Sep 22, 2009
I am trying to clean up my code in a project I have been working on by creating two separate modules one that disables a service and one that enables a service through the registry all of this worked fine in one big form all together but I would like to also reuse the module in some other projects, I am getting this message however "Warning1Function 'ApplicationLayerGatewayDisable' doesn't return a value on all code paths. A null reference exception could occur at run time when the result is used". [Code]. what do i need to do to get rid of these warnings ? or do I just ignore them?
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Jan 9, 2009
I'm creating an application in which i have 5 picture boxes on top of each other that will "layer" pictures on top of each other. The user can show and hide certain layers by checking / unchecking check boxes. I need all the layers to be transparent so the prior layer can show through. Currently all layers are set to transparent back color however, in VB8, controls by default don't support transparent colors. MSDN says you can override this and give controls transparency by the following:
Locate the constructor for your control class. The constructor appears in the control's code file. In C#, the constructor is the method with the same name as the control and with no return value. In Visual Basic, the constructor is the method named New. Call the SetStyle method of your form in the constructor.
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