What is a Typed Dataset in ADO.NET? Why do we use a Typed DataSet? What is the difference between a Typed and an UnTyped DataSet?

Typed DataSet - When a created DataSet derives from the DataSet class, that applies the information contained in the XSD to create a Typed class, this DataSet is said to be a Typed Dataset. Information from the schema whic comprises the tables, columns, and rows is created and compiled to a new DataSet derived from the XSD. The Typed DataSet class features all functionality of the DataSet class. This may be used with methods that take an instance of the DataSet class as a parameter.

Note that an UnTyped DataSet does not have any schema. It is exposed simply as a mere collection.

How to create a Typed DataSet? -
Write click your project in the Solution Explorer.
Click Add New Item.
Select DataSet.

This adds a new XSD to the project. The schema created may be viewed as an XML. When this xsd file is compiled, two files are created by Visual Studio. The first file that contains the .vb or .cs extension contains the information about the proxy class. This class contains methods & properties that are required to access the database
data. The second file has an extension xsx and this contains information about the layout of the XSD.

What is Diffgram in ADO.NET? When do we use Diffgram?

A DiffGram is an XML format. It is used to identify current and original versions of data elements. A DataSet may use a DiffGram format to load and persist the contents, and further to serialize its contents for porting across a network connection. Whenever a DataSet is written as a DiffGram, the DataSet populates the DiffGram with all the important information to accurately recreate the contents. Note that schema of the DataSet is not recreated. This includes column values from both the Current and the Original row versions, row error information, and row order.

What is DataRelation object in ADO.NET? How to use a DataRelation between two columns in ADO.NET?

In order to set the relationship between two or more than two columns, ADO.NET provides the DataRelation class. When a DataRelation object is created, it assists to enforce some constraints on the relationships between columns. The constraint may be like a Unique constraint that ensures that a column will have no duplicate value in the table. A Foreign Key constraint may be used to enforce Referential Integrity. The Unique property may be set by setting the Unique property of a DataColumn to True. This may also be done by adding an instance of the UniqueConstraint class to the DataRelation object. As a part of the foreign key constraint, we may specify referential integrity rules that are applied at 3 places

1) When a parent record is updated
2) When a parent record is deleted
3) When a change is rejected or accepted.

A DataRelation object permits to establish a parent-child relationship between two or more tables inside a DataSet object. The easiest way to create a DataRelation between two tables in a DataSet is to setup a primary key - foreign key relationship between the columns of a table.

See code example below, where a DataRelation has been setup between the Employee table and the Salary table...

'Code Below in VB.NET
Dim Conn As SqlConnection
Dim da As SqlDataAdapter
Dim ds As DataSet
Dim RowParent As DataRow
Dim RowChild As DataRow

Conn = New _
SqlConnection(ConfigurationSettings.Appsettings("SomeConnectionStringWrittenInWeb.Config"))
da = New SqlDataAdapter("SELECT * FROM Employees", Conn)
ds = New DataSet()

Try
Conn.Open()
da.Fill( ds,"Employees")
da.SelectCommand = New SqlCommand("SELECT * FROM Salary", Conn)
da.Fill(ds, "Salary")
Catch ex As SqlException
Response.Write(ex.ToString())
Finally
Conn.Dispose()
End Try

'Next, Let us create a Data Relationship
ds.Relations.Add("Employee_Salary", ds.Tables("Employees").Columns("EmployeeID"), _
ds.Tables("Salary").Columns("EmployeeID"))
'Display the Employee and Child Salary in the Form
'Say we have a Label in the form
For each RowParent in ds.Tables("Employees").Rows

lblRelation.Text &= RowParent("Emp_Name")
For each RowChild in RowParent.GetChildRows("Employee_Salary")
lblRelation.Text &= "
" & RowChild("Sal_Amount")
Next
Next

What is a DataView in ADO.NET?

DataView - Just like we have Views in SQL (in our backend), we have DataView object in ADO.NET. A dataview object represents bindable, customized view of a DataTable object. Operations like Sorting, Filtering, Searching, Editing and Navigation may be performed on a DataView object. In scenarios like retrieval of a subset of data from a Datatable, we may make use of DataViews to get this data. Note that the DefaultView property of a DataTable returns the Default data view for the DataTable. In case a custom view of a DataTable has to be created on a DataView, then the RowFilter property of the DataView is set to the DefaultView.

A dataview may also be used to sort data that resides in it in ascending or descending order. Below is code on how to sort data in a dataview in ascending or descending order...

DataView objdv = new DataView();
objdv.Sort("ColumnName Asc|Desc");