Implementing a 3-Tier architecture with C# – Part 5


Hi back,

In this post we will finalize the implementation of our 3-tier asp.net architecture, by developing a Web-based presentation layer.

So far, we have developed the data access and business layers. The implementation of UI, consists of methods and approaches for handling business and crud operations thorough a Web UI. In fact, there are several ways to present business objects and reflect the changes back to data base. Like:

  1. Binding controls (i.e. GridView) directly to DataTables coming from business classes (i.e. by FetchAll method)
  2. Binding controls (.e. GridView) to business classes using an IDataSource, like ObjectDataSouce control.
  3. Mixing up the above methods.

If you opt the first option, you need to handle sorting and paging manually. It means that you have to write code for PageIndexChanged and Sorted methods. This might take several minutes for you to handle every details and make your development process too long and not productive.

A better approach is using ObjectDataSource. For using it, we have to prepare our business classes first. ObjectDataSoruce works with classes that DataObject attribute has been applied to them. Thus, open your business class (i.e. PersonBiz.cs), and apply DataObject attribute on it:

[DataObject]

public class PersonBiz
{ …

Then we might specify four methods for doing Select/Insert/Update/Delete operations. However, I personally prefer to use Select method only and do the other operations manually. My reason is that, if I declare a method for Insert/Update methods, I will have to use GridView’s (or similar controls) editing features and have to pass a lot of params to the Insert/Update methods. and I do not like it! πŸ™‚

Anyway, to mark a method as a Select method, we have to apply DataObjectMethod attribute on it. This attribute takes a parameter indicating which kind of method is it. For example, a select method can be declared like this:
[DataObjectMethod(DataObjectMethodType.Select)]
public DataTable FetchAll(…

If you are intended to use ObjectDataSource, your Select method must have a return value of type IENumerable, and preferably, it would better return a DataTable or DataView.Thus, FetchAll method returns a DataTable. It also has two parameters as follows:

[DataObjectMethod(DataObjectMethodType.Select)]
public DataTable FetchAll(int startRowIndex, int maximumRows)
{
PersonEntity entity = new PersonEntity();
innerDAL.Fill(entity, startRowIndex, maximumRows);
return entity;
}

As you see, the startRowIndex and maximumRows are used for paging. If you do not wish to manage paging, you may omit these two arguments.

To bind your UI control (i.e. GridView) to this method, put an ObjectDataSource on your web form. Then, choose Configure DataSource from it’s smart tag. The Configure Data Source window will open:

Check the “Show only data components” and open the drop down list beside it. If nothing is seen, you have to build the BusinessLayer.Dll and put it in your website’s Bin folder.

Select your business class and click Next. At the next step, you have to specify which methods are used for Select, Insert, Update and Delete operations. The following image is an example :

After choosing all your methods, click Finish to close this dialog. If you are going to let the ObjectDataSource handle the paging operation, go to your page’s source code, find the code of GridView control and remove the SelectParameters. This is necessary because startRowIndex and maximumRows will be provided by ObjectDataSource control. If you do not remove them, you will get an error message.

In order to activate paging in ObejctDataSource, you have to set its EnablePaging property to True. you also have to set the AllowPaging property of your GridView control to true. In order for ObjectDataSource to do paging operation correctly, we have to tell it how many records are in database. Therefore, there must be a public method in our business class that return the total number of rows in DB. What we need is to assign it’s name to SelectCountMethod property of ObjectDataSource. You do not need to flag this property with an attribute:

public int GetTotalRecordCount()
{
return innerDAL.GetTotalRecordCount();
}

Notice that if you are filtering the results of your SelectMethod, for example by passing a filter string to it, you have to perform the same filter on the result of SelectCountMethod.

Now build and run your website. you will see that the data is being shown and the grid supports sorting and paging very well. To ensure that paging is working correctly, run Microsoft Sql Server Profiler, and check to see if the Select SQL statement has correct startRowIndex and maximumRowCount values.

To insert a new record, you may create a new entity (i.e. PersonEntity) , fill it and save it to DB.

To update a record, retrieve the record from database using it’s Primary Key, edit it and save it back to db.

To delete a record, perform a delete operation on database using the records PK.

But how to obtain the record’s Primary Key? You may save it somewhere in UI when the UI control is getting bound. To do this, I usually write such a code in RowDataBound event :

if (e.Row.RowType == DataControlRowType.DataRow)
{
int Serial = DataBinder.Eval(e.Row.DataItem, “Serial”);
e.Row.Cells[0].Attributes.Add(“Serial”, Serial.ToString());
}

In the above code, if the row being bound is a data row (not footer or header), we get the value of “Serial” column and store it in the 1st cell of the current row. Notice that whatever toy add yo .Attributes collection will be available to the rendered html page. Thus, never save passwords or other sort of crucial data with this method.

Now, for each row, you have the Primary Key value. Therefore, we may perform update and delete operations easily. Not keeping the whole data in memory (or in ViewState), increases the access to data base, but reduces the usage of server’s resources. However, it is up to you and your project’s conditions to decide that method should be used.

You may download a full example of this implementation HERE. Please note that the file is password protected and it’s password is : aspguy.wordpress.com

Bye for now..


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