The document summarizes key objects and concepts related to working with data in .NET, including: - The DataTable object represents tabular data as rows and columns and is used to hold data in memory for disconnected data operations. It contains DataRow objects that hold data. - The DataSet is a memory-based representation of relational data that can contain multiple related DataTable objects and DataRelation objects defining relationships between tables. - Other objects like DataColumn, DataView, and DataRow are used to define and interact with data in DataTable and DataSet objects, including sorting, filtering, and relating rows between tables. Data can be loaded, modified, and serialized to files or streams for transfer.

2.  DataTable
 DataColumn
 DataRow
 DataView
 DataSet

3.  The DataTable object represents tabular data as
rows, columns, and constraints.
 Use the DataTable object to hold data in
memory while performing disconnected data
operations.
 Can get a DataTable object by connecting to the
database and returning table data.

4.  Can be explicitly created by instantiating the
DataTable class
 You then add DataColumn objects to the class to
define the type of data to be held.
 The DataColumn objects also contain constraints.
 Once the DataTable is defined with columns, you
can add DataRow objects that contain data for the
table.

5. private DataTable GetDataTable()
{
DataTable employee = new DataTable("Employee");
DataColumn eid = new DataColumn("Eid");
eid.DataType = typeof(string);
eid.MaxLength = 10;
eid.Unique = true;
eid.AllowDBNull = false;
eid.Caption = "EID";
employee.Columns.Add(eid);
return employee;
}

6.  DataType
 MaxLength
 Unique
 AllowDBNull
 Caption

7.  The primary key of a DataTable object consists of
one or more columns that define data that
represent a unique identity for each row in the
data.
employee.PrimaryKey = new DataColumn[] {eid};

8.  The DataTable object contains a Rows
collection, which contains a collection of
DataRow objects.
 You can insert data into the Rows collection by
using
 Add method on the Rows collection
 Load method on the DataTable object.

9. DataRow newemployee = employee.NewRow();
newemployee["Eid"] = "123456789A";
newemployee["FirstName"] = "Nancy";
newemployee["LastName"] = "Davolio";
newemployee["Salary"] = 10.00m;
employee.Rows.Add(newemployee);
Or
employee.Rows.Add("987654321X", "Andrew", "Ful
ler", 15.00m);

10. employee.LoadDataRow( new object[]
{ "987654321X", "Janet", "Leverling", 20.00m },
LoadOption.OverwriteChanges);
 LoadOption enumeration value that has one of
the following values:
 OverwriteChanges
 PreserveChanges
 Upsert

11.  Detached : DataRow is created but not
added to a DataTable.
 Added : DataRow is added to a DataTable.
 Unchanged : DataRow has not changed
since the last call to the AcceptChanges
method. The DataRow changes to this state
when the AcceptChanges method is called.
 Modified : DataRow has been modified
since the last time the AcceptChanges
method was called.
 Deleted : DataRow is deleted using the
Delete method of the DataRow.

13.  The AcceptChanges method is used to reset the
DataRow state to Unchanged.
 After data has been loaded from the database, the
RowState property of the loaded rows is set to Added.
 Calling AcceptChanges on the DataTable resets the
RowState of all of the DataRow objects to Unchanged.
 If you modify the DataRow objects, their RowState
changes to Modified.
 After the changes have been successfully sent to the
data store by calling the AcceptChanges method the
RowState changes to Unchanged.

14.  The Delete method on the DataRow is used to set the
RowState of the DataRow to Deleted.
 There are many scenarios where you need to undelete a
DataRow.
 The DataRow object doesn’t have an undelete
method, but you can use the RejectChanges method to
perform an undelete that may satisfy some scenarios.

15.  The DataRow object can hold up to three versions, or copies, of
the data: Original, Current, and Proposed.
 When the DataRow is created, it contains a single copy of the
data, which is the Current version.
 When the DataRow is placed into edit mode by executing its
BeginEdit method, changes to the data are placed in a second
version of the data, called the Proposed version.
 When the EndEdit method is executed, the Current version
becomes the Original version, the Proposed version becomes
the Current version, and the Proposed version no longer exists.

 After EndEdit has completed its execution, there are two
versions of the DataRow data: Original and Current.

16.  You often need to create a full copy of a DataTable in
your application.
 For example, you might want to assign a DataTable
object to a GridView control to allow a user to edit the
data, but you also might want to provide a cancel
button that aborts all changes on the Web page.
 A simple way to implement this functionality is to
create a copy of your DataTable object and use the copy
for editing.
 DataTable copy = employee.Copy();

17.  You often require a copy of the DataTable schema
without the data.
 You can accomplish this by invoking the Clone method
on the DataTable.
 Use this method when an empty copy of the DataTable
is required and to which DataRow objects will be added
at a later time.
DataTable clone = employee.Clone();
clone.ImportRow(employee.Rows[0]);
 The ImportRow method on the DataTable object copies
a DataRow from a DataTable that has the same schema.

18.  The DataView object provides a window into a
DataTable that can be sorted and filtered using the
Sort, RowFilter, and RowStateFilter properties.
 A DataTable can have many DataView objects assigned
to it, allowing the data to be viewed in many different
ways without requiring the data to be reread from the
database.
 The DataView object also contains the
AllowDelete, AllowEdit, and AllowNew properties to
constrain user input as needed.

19. protected void Button7_Click(object sender, EventArgs e)
{
//get datatable
DataTable employee = GetDataTable();
//sort and display
DataView view = new DataView(employee);
view.Sort = "LastName ASC, FirstName ASC, Salary DESC";
GridView1.DataSource = view;
GridView1.DataBind();
}
Also RowFilter can be set to a SQL WHERE clause without the
word “WHERE.”
view.RowFilter = "LastName like 'A%' and Salary > 15";

20.  The DataSet is a memory-based relational
representation of data and the primary disconnected
data object.
 The DataSet contains a collection of DataTable and
DataRelation objects.

21. private DataSet GetDataSet()
{
DataSet companyData = new DataSet("CompanyList");
DataTable company = companyData.Tables.Add("company");
company.Columns.Add("Id", typeof(Guid));
company.Columns.Add("CompanyName", typeof(string));
company.PrimaryKey = new DataColumn[] { company.Columns["Id"] };
DataTable employee = companyData.Tables.Add("employee");
employee.Columns.Add("Id", typeof(Guid));
employee.Columns.Add("companyId", typeof(Guid));
employee.Columns.Add("LastName", typeof(string));
employee.Columns.Add("FirstName", typeof(string));
employee.Columns.Add("Salary", typeof(decimal));
employee.PrimaryKey = new DataColumn[] { employee.Columns["Id"] };
companyData.Relations.Add(
"Company_Employee",
company.Columns["Id"],
employee.Columns["CompanyId"]);
return companyData;

22. Label lbl = GetLabel(275, 20);
DataSet companyList = GetDataSet();
DataRelation dr = companyList.Relations["Company_Employee"];
DataRow companyParent = companyList.Tables["company"].Rows[1];
lbl.Text = companyParent["CompanyName"] + "<br />";
foreach (DataRow employeeChild in companyParent.GetChildRows(dr))
{
lbl.Text += "&nbsp;&nbsp;&nbsp;" + employeeChild["Id"] + " "
+ employeeChild["LastName"] + " "
+ employeeChild["FirstName"] + " "
+ string.Format("{0:C}", employeeChild["Salary"]) + "<br />";
}
lbl.Text += "<br /><br />";
DataRow employeeParent = companyList.Tables["employee"].Rows[1];
lbl.Text += employeeParent["Id"] + " "
+ employeeParent["LastName"] + " "
+ employeeParent["FirstName"] + " "
+ string.Format("{0:C}", employeeParent["Salary"]) + "<br />";
DataRow companyChild = employeeParent.GetParentRow(dr);
lbl.Text += "&nbsp;&nbsp;&nbsp;" + companyChild["CompanyName"] + "<br />";

23.  A DataSet can be serialized as XML or as binary data to
a stream or file.
 The DataSet can also be deserialized from XML or
binary data from a stream or file. The serialized data
can be transferred across a network via many
protocols, including HTTP.