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Databases Fundamentals: Data Records
 

Tables Records
 

Introduction to Records

In our description of tables, we saw that a table was made of one or various columns that represented categories of data. After creating such a table and its columns that represent the categories, you (actually the user) can enter values in the table to make it a valuable list. Filling up a table with values is referred to as data entry.

Data entry is performed by entering a value under the column headers. The group of values that correspond to the same entry or the same line under the columns is called a record. This also means that the records are entered one line, also called a row, at a time. Here is a table filled with various records:

A record on a table is represented as a row (horizontal) of data. To support the various records that belong to a table, the DataTable class is equipped with a property called Rows. The DataTable.Rows property is in fact an object of the DataRowCollection class. The DataRowCollection class provides the necessary properties and methods you can use to create and manage records of a table. A row itself is an object based on the DataRow class.

 
This lesson is done in two parts: the explanation of database topics and the Practical Learning sections intended to apply the concepts. The explanation sections are as complete as possible so you don't have to follow the Practical Learning exercises. But if you want to perform the assignments in the Practical Learning sections, you must be familiar with the list view control.
 

Practical Learning Practical Learning: Introducing Data Records
  1. Start Microsoft Visual Studio .NET and create a new Windows Forms Application named AddressBook1
  2. In the Toolbox, click the Data button.
    To create a DataSet, click DataSet and click the form
     
  3. In the Add Dataset dialog box, click the Untyped Dataset radio button and click OK
  4. While the DataSet control is still selected, in the Properties window, click (Name) and type dsAddressBook
  5. Still in the Properties window, set the DataSetName to AddressBook
  6. Right-click the form and click View Code
  7. In the top section of the file, under the other using lines, type:
      
    using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO;
using System.Xml;
using System.Globalization;
  8. In the class of the form, declare a string variable named strFilename
      
    public class Form1 : System.Windows.Forms.Form
{
	private string strFilename;
  9. Return to the form and double-click its body
  10. Implement its Load event as follows:
      
    private void Form1_Load(object sender, System.EventArgs e)
{
	// This is the file that will hold the records
	strFilename = "PeopleInMyLife.xml";

	// If that file exists already, open it
	if( File.Exists(strFilename) )
		this.dsAddressBook.ReadXml(strFilename);
	else // If it doesn't exist already, then create it
		this.dsAddressBook.WriteXml(strFilename);
}
  11. Return to the form.
    As done for the lesson on columns, under the form, click dsPeople if necessary. In the Properties window, click the Tables field to reveal its ellipsis button ellipsis
  12. Click the ellipsis button ellipsis
  13. In the Tables Collection Editor, click the Add button and change its properties as follows:
    (Name): tblPersons
    TableName:     Persons
  14. Click the Columns field to reveal its ellipsis button ellipsis and click its ellipsis button ellipsis. In the Columns Collection Editor, click the Add button and, from what we learned about tables and columns, create the columns as follows:
     
    Table Column (Name) ColumnName Data Type
    Persons colFullName FullName  
    Persons colFriendlyName FriendlyName  
    Persons colGender Gender  
    Persons colRelationshipType TypeOfRelationship  
    Persons colKnownSince KnownSince  
    Persons colCurrentResidence CurrentResidence  
    Persons colPhoneNumber PhoneNumber  
    Persons colLastUpdate LastUpdate  
    Persons colNotifyIfEmergency NotifyIfEmergency System.Boolean
  15. Click Close twice
  16. Design the form as follows:
     
    Control Name Text Other Properties
    ListView lvwPeople   AllowColumnReorder: True
    Anchor: Top, Bottom, Left, Right
    FullRowSelect: True
    GridLines: True
    Button btnClose Close Anchor: Bottom, Right
  17. Double-click the Close button and implement its Click event as follows:
      
    private void btnClose_Click(object sender, System.EventArgs e)
{
	Close();
}
  18. Return to the form.
    Change the list view's View property to Details and click the ellipsis button of its Columns property
  19. Click Add and create the columns as follows:
     
    Column (Name) Text TextAlign Width
    FullName Full Name   120
    FriendlyName Friendly Name   80
    Gender Gender Center  
    Relationship Relationship   80
    KnownSince Known Since   100
    CurrentResidence Current Residence   100
    PhoneNumber Phone #   80
    LastUpdate Last Update Right 80
    NotifyIfEmergency Notify? Center  
  20. Click OK

Introduction to Data Entry

To allow the user to perform data entry, you must create an appropriate object meant for this task. You have various options. You can use various controls on the same view or provide a data sheet type of view such as the one available from the DataGrid control. In all cases, when the user performs data entry, by default, it is by entering one record at a time. Any time while the user is performing an operation on a record, the record has a status that can be identify by the DataRow.RowState property which is a value based on the DataRowState enumerator.

A record on a table is represented as a row of data. To support the various records that belong to a table, the DataTable class is equipped with the Rows property which is an object of type DataRowCollection with each record an object of type DataRow.

Before adding a new record to a table, you must let the table know. This is done by calling the DataTable.NewRow() method. Its syntax is:

public DataRow NewRow();

The DataTable.NewRow() method returns a DataRow object. Here is an example:

 
private void btnCreate_Click(object sender, System.EventArgs e)
{
	dtDirectors = new DataTable();
	DataRow rowDirector = this.dtDirectors.NewRow();
}
 

Practical Learning Practical Learning: Introducing Data Entry
  1. In the Windows Forms section of the Toolbox, click ContextMenu and click the form
  2. On the form, click ContextMenu and click Type Here. Create the following menu items:
     
    Text (Name) Shortcut
    New Person mnuNewPerson CtrlN
    Edit Details mnuEditDetails CtrlE
    Delete Person mnuDelete Del
    Remove all People mnuRemoveAll ShiftDel
  3. On the form, click the list view. In the Properties window, set its ContextMenu to contextMenu1
  4. To create a new form, on the main menu, click Project -> Add Windows Form...
  5. Set the Name to NewPerson and press Enter
  6. Design the form as follows:
     
    Control Name Text Other Properties
    Label   Full Name:  
    TextBox txtFullName   Modifiers: Public
    Button btnCreate Create DialogResult: OK
    Modifiers: Public
    Label   Friendly Name:  
    TextBox txtFriendlyName   Modifiers: Public
    Button btnClose Close DialogResult: Cancel
    Label   Gender:  
    ComboBox cboGenders Unknown Modifiers: Public
    Items: Female, Male,
    Unknown
    Relationship cboRelationships Undefined Modifiers: Public
    Items: Friend, Wife, Husband, Son, Daughter, Father, Mother, Brother, Sister, Uncle, Aunt, Cousin, Nephew, Niece, Classmate, Co-Worker, Boss, Employee, Business Partner
    Sorted: True
    Label   Known Since:  
    TextBox txtKnownSince   Modifiers: Public
    Label   Current Residence:  
    TextBox txtCurrentResidence   Modifiers: Public
    Label   Phone Number:  
    TextBox txtPhoneNumber   Modifiers: Public
    Label   Last Update:  
    DateTimePicker dtpLastUpdate   Modifiers: Public
    Format: Custom
    CustomFormat: dddd dd MMM yyyy
    CheckBox chkNotify Notify in case of emergency? Modifiers: Public
  7. In the Class View, expand everything. Right-click Form1 -> Add -> Add Method...
  8. Set the Method Access to internal, the Return Type to void, the Method Name to RefreshPeople and press Enter
  9. Implement the method as follows:
      
    internal void RefreshPeople()
{
	if( File.Exists(strFilename) )
	{
		this.lvwPeople.Items.Clear();
		XmlDocument xmlPeople = new XmlDocument();
		xmlPeople .Load(strFilename);

		XmlElement nodRoot = xmlPeople.DocumentElement;
		XmlNodeList nodFullNames = nodRoot.GetElementsByTagName("FullName");
		XmlNodeList nodFriendlyNames = nodRoot.GetElementsByTagName("FriendlyName");
		XmlNodeList nodGenders = nodRoot.GetElementsByTagName("Gender");
		XmlNodeList nodRelationships  = nodRoot.GetElementsByTagName("TypeOfRelationship");
		XmlNodeList nodKnownDates  = nodRoot.GetElementsByTagName("KnownSince");
		XmlNodeList nodResidences = nodRoot.GetElementsByTagName("CurrentResidence");
		XmlNodeList nodPhoneNumbers = nodRoot.GetElementsByTagName("PhoneNumber");
		XmlNodeList nodLastUpdates = nodRoot.GetElementsByTagName("LastUpdate");
		XmlNodeList nodNotifications = nodRoot.GetElementsByTagName("NotifyIfEmergency");

		for(int i = 0; i < nodFullNames.Count; i++)
		{
			ListViewItem lviPeople = new ListViewItem(nodFullNames[i].InnerText);
			lviPeople.SubItems.Add(nodFriendlyNames[i].InnerText);
			lviPeople.SubItems.Add(nodGenders[i].InnerText);
			lviPeople.SubItems.Add(nodRelationships[i].InnerText);
			lviPeople.SubItems.Add(nodKnownDates[i].InnerText);
			lviPeople.SubItems.Add(nodResidences[i].InnerText);
			lviPeople.SubItems.Add(nodPhoneNumbers[i].InnerText);
			lviPeople.SubItems.Add(nodLastUpdates[i].InnerText);
			lviPeople.SubItems.Add(nodNotifications[i].InnerText);
			this.lvwPeople.Items.Add(lviPeople);
		}
	}
}
  10. In the Types combo box above the Code Editor, make sure Form1 is selected. In the Members combo box, select Form1_Load
  11. Change the Load event as follows:
      
    private void Form1_Load(object sender, System.EventArgs e)
{
	// This is the file that will hold the records
	strFilename = "PeopleInMyLife.xml";

	// If that file exists already, open it
	if( File.Exists(strFilename) )
	{
		this.dsAddressBook.ReadXml(strFilename);
		RefreshPeople();
	}
	else // If it doesn't exist already, then create it
		this.dsAddressBook.WriteXml(strFilename);
}
  12. Save all

Data Entry
 

Adding a Value Based on the Column Index

When you call the DataTable.NewRow() method, the record's status is DataRowState.Detached. After calling the DataTable.NewRow() method, you can specify the value that the column would carry. To do this, you must specify the table's column whose value you want to provide. You can locate a column based on an index as we mentioned already that the columns of a table are stored in the DataTable.Columns property which is based on the DataColumnCollection class. Each column can be identified by its index. Using this index, to assign a new value to the column, you can use the following version of the DataRow property:

public object this[int columnIndex] {get; set;}

Here is an example:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	dtDirectors = new DataTable();
	DataRow rowDirector = this.dtDirectors.NewRow();

	rowDirector[0] = "Jonathan Demme";
}

When the record has been added to the table, the record has a status of DataRowState.Added. The above version of the DataRowCollection.Add() method allows you to add a value for one column. To complete a record, you would have to create a value for each column.
 

Practical Learning Practical Learning: Adding a Value Based on the Column Index
  1. Display the first form and click contextMenu1. On the form, click Context Menu and double-click New Person
  2. To create a record using the column's indices, implement the event as follows:
      
    private void mnuNewPerson_Click(object sender, System.EventArgs e)
{
	NewPerson dlgPerson = new NewPerson();

	if( dlgPerson.ShowDialog() == DialogResult.OK )
	{
		DataRow rowPerson = this.tblPersons.NewRow();
		rowPerson[0] = dlgPerson.txtFullName.Text;
		rowPerson[1] = dlgPerson.txtFriendlyName.Text;
		rowPerson[2] = dlgPerson.cboGenders.Text;
		rowPerson[3] = dlgPerson.cboRelationships.Text;
		rowPerson[4] = dlgPerson.txtKnownSince.Text;
		rowPerson[5] = dlgPerson.txtResidence.Text;
		rowPerson[6] = dlgPerson.txtPhoneNumber.Text;
		rowPerson[7] = dlgPerson.dtpLastUpdate.Value.ToString("d");
		rowPerson[8] = dlgPerson.chkNotify.Checked.ToString();
		this.tblPersons.Rows.Add(rowPerson);

		this.dsAddressBook.WriteXml("PeopleInMyLife.xml");
		RefreshPeople();
	}
}
  3. Execute the application to test it and try creating a few persons
     
  4. Close the form(s) and preview the XML file in your browser
     
  5. Return to your programming environment

Adding a Value Based on the Column Variable Name

If you prefer to use the variable name of a column when adding the value, you can use the following version of the property:

public object this[DataColumn column] {get; set;}

Here is an example of using this version of the property:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	dtDirectors = new DataTable();
	DataRow rowDirector = this.dtDirectors.NewRow();

	rowDirector[0] = "Jonathan Demme";
	DataRow rowCategory = this.dtVideoCategories.NewRow();

	rowCategory[this.colCategory] = "Documentary";	
}
 

Practical Learning Practical Learning: Adding a Value Based on the Column Variable Name
  1. Display the form and add a new Button
  2. Set its properties as follows:
    (Name): btnNewPerson
    Text: New Person
    Anchor: Bottom, Left
     
  3. Double-click the new button and implement its Click event as follows:
      
    private void btnNewPerson_Click(object sender, System.EventArgs e)
{
	NewPerson dlgPerson = new NewPerson();

	if( dlgPerson.ShowDialog() == DialogResult.OK )
	{
		DataRow rowPerson = this.tblPersons.NewRow();
		rowPerson[colFullName] = dlgPerson.txtFullName.Text;
		rowPerson[colFriendlyName] = dlgPerson.txtFriendlyName.Text;
		rowPerson[colPersonGender] = dlgPerson.cboGenders.Text;
		rowPerson[colRelationshipType] = dlgPerson.cboRelationships.Text;
		rowPerson[colKnownSince] = dlgPerson.txtKnownSince.Text;
		rowPerson[colCurrentResidence] = dlgPerson.txtResidence.Text;
		rowPerson[colPhoneNumber] = dlgPerson.txtPhoneNumber.Text;
		rowPerson[colLastUpdate] = dlgPerson.dtpLastUpdate.Value.ToString("d");
		rowPerson[colNotifyIfEmergency] = dlgPerson.chkNotify.Checked.ToString();
		this.tblPersons.Rows.Add(rowPerson);

		this.dsAddressBook.WriteXml("PeopleInMyLife.xml");
		RefreshPeople();
	}
}
  4. Execute the application and try creating a few persons using the New Person button
     
  5. Close the form(s) and return to your programming environment

Adding a Value Based on the Column Object Name

To specify the name of the column, the DataRow class is equipped with an Item property that allows you to identify a column by its object name, by its variable name, or by its index. Based on this, the DataRow property is overloaded with three versions. One of the versions uses the following syntax:

public object this[string columnName] {get; set;}

This property expects the object name of the column passed in its square brackets. When calling this property, you can assign it the desired value for the column. Here is an example:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	DataRow rowDirector = this.dtDirectors.NewRow();

	rowDirector["Director"] = "John Landi";
}

After assigning the desired value to the row, to add the new value to a table, the DataRowCollection class provides the Add() method that is overloaded with two versions. The first version of this method uses the following syntax:

public void Add(DataRow row);

This method simply expects you to pass the DataRow object you previously defined. Here is an example:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	DataRow rowDirector = this.dtDirectors.NewRow();

	rowDirector["Director"] = "John Landi";
	this.dtDirectors.Rows.Add(rowDirector);
}

In the same way, you can identify each column of a table by its object name and assign it the appropriate value. Once the record is complete, you can add it to the table. Here is an example:

 
private void btnCreate_Click(object sender, System.EventArgs e)
{
	 DataRow rowVideo = this.dtVideos.NewRow();

	 rowVideo["Title"] = "A Few Good Men";
	 rowVideo["Director"] = "Rob Reiner";
	 rowVideo["YearReleased"] = 1993;
	 rowVideo["Length"] = "138 Minute";
	 rowVideo["Rating"] = "R";
	 rowVideo["Format"] = "VH";
	 rowVideo["Category"] = "Drama";
	 this.dtVideos.Rows.Add(rowVideo);
}
 

Practical Learning Practical Learning: Adding a Value Based on the Column Object Name
  1. Display the form and click the list view
  2. In the Properties window, click the Events button and double-click the right field to KeyDown
  3. Implement the event of the list view as follows:
      
    private void lvwPeople_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
	// If the user pressed F4...
	if( e.KeyCode == Keys.F4 )
	{
		// ... Get ready to create a new record
		NewPerson dlgPerson = new NewPerson();

		if( dlgPerson.ShowDialog() == DialogResult.OK )
		{
			DataRow rowPerson = this.tblPersons.NewRow();
			rowPerson["FullName"] = dlgPerson.txtFullName.Text;
			rowPerson["FriendlyName"] = dlgPerson.txtFriendlyName.Text;
			rowPerson["Gender"] = dlgPerson.cboGenders.Text;
			rowPerson["TypeOfRelationship"] = dlgPerson.cboRelationships.Text;
			rowPerson["KnownSince"] = dlgPerson.txtKnownSince.Text;
			rowPerson["CurrentResidence"] = dlgPerson.txtResidence.Text;
			rowPerson["PhoneNumber"] = dlgPerson.txtPhoneNumber.Text;
			rowPerson["LastUpdate"] = dlgPerson.dtpLastUpdate.Value.ToString("d");
			rowPerson["NotifyIfEmergency"] = dlgPerson.chkNotify.Checked.ToString();
			this.tblPersons.Rows.Add(rowPerson);

			this.dsAddressBook.WriteXml("PeopleInMyLife.xml");
			RefreshPeople();
		}
	}
}
  4. Execute the application
  5. Press F4 and try creating a person
     
  6. Close the form(s) and return to your programming environment

Adding an Array of Records

The above version of the DataRowCollection.Add() method means that you must identify each column before assigning a value to it. If you already know the sequence of columns and don't need to explicitly identify them, you can store all values in an array and simply add the array as a complete record. To do this, you can use the second version of the DataRowCollection.Add() method whose syntax is:

public virtual DataRow Add(object[] values);

Here is an example:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	 string[] vdoRecord = { "Fatal Attraction", "Adrian Lyne", "1987",
			       "120 Minute", "R", "DVD", "Drama" };

	 this.dtVideos.Rows.Add(vdoRecord);
}

There is an alternative to this second version of the DataRowCollection.Add() method. As opposed to passing an array of values to the Add() method, you can first define an array, assign that array to a DataRow variable, then pass that DataRow object to the Add() method. To support this technique, the DataRow class is equipped with an ItemArray property that expects an array. Here is an example

private void btnCreate_Click(object sender, System.EventArgs e)
{
	 string[] vdoNewVideo = { "Her Alibi", "Bruce Beresford", "1989",
			             "94 Minute", "PG-13", "DVD", "Comedy" };
	 DataRow rowNewVideo = this.dtVideos.NewRow();
	 rowNewVideoArray = vdoNewVideo;
	 this.dtVideos.Rows.Add(rowNewVideo);
}

After creating the records of a table, if a record contains invalid values, the DataRow.HasErrors property can help you identify them.

Locating Records and Their Values
 

Locating a Record

Before performing any operation on a record, you must be able to locate it. That is, you must be able to identify a record among the various records of a table. To locate a record in the DataTable.Rows collection, the DataRowCollection class provides the Item property that is defined as follows:

public object this[int columnIndex] {get; set;}

The records of a table are stored in a list (called the DataRowCollection). The first record, which in the example above has the title as "A Few Good Men" and the Director as "Rob Reiner", has an index of 0. The second record has an index of 1, and so on. Here is an example of using it to retrieve the information stored in a record:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	DataRow row = this.dtVideos.Rows[2];
}

When you pass an index to this property, the compiler would check whether the record exists. If a record with that index exists, its DataRow value is produced. If you specify an index that is either less than 0 or beyond the number of records in the table, the compiler would throw an IndexOutOfRangeException exception.

To get the number of records that a table contains, access the Count property of its DataRowCollection. The Count property is inherited from the InternalDataCollectionBase class, which is the parent of many collection classes.

When the records of a DataTable object have been created, you can get their list as an array using its List property that is inherited from the InternalDataCollectionBase class. This property returns an ArrayList type of list.
 

Practical Learning Practical Learning: Locating a Record
  1. Display the first form and click the list view
  2. In the Events section of the Properties window, double-click the right field to DoubleClick and implement its event as follows:
      
    private void lvwPeople_DoubleClick(object sender, System.EventArgs e)
{
	ListViewItem selPerson = this.lvwPeople.SelectedItems[0];
	int indexOfPersonSelected = selPerson.Index;
	DataRow rowPerson = this.tblPersons.Rows[indexOfPersonSelected];
}
  3. Save all

Locating a Value

As mentioned already, a record is in fact one value or a group of values from each of the columns of the table. Consider the following table:

The "A Few Good Men" string is a value of the Title column. In the same way, "VH" is a value of the Format column. In some circumstances, you will need to locate a particular value in order to perform an operation on it. As seen above, you can start by locating the record you need and return its DataRow object. To know the table that the record belongs to, access its DataRow.Table property. This property is declared as follows:

public DataTable Table {get;}

To locate the value that a record holds under a particular column, the DataRow class provides the Item property that is overloaded with three versions (actually six, but we are interested in the first three only). One of the versions of this property uses the following syntax:

public object this[string columnName {get; set;}

To use this property, pass the object name of the column in the square brackets. The following example is based on the above table. It retrieves the title of the third video and displays it in the caption of the form:

private void btnCreate_Click(object sender, System.EventArgs e)
{
	 DataRow row = this.dtVideos.Rows[2];
	 string  strVideoTitle = (string )(row["Title"]);

	 Text = strVideoTitle;
}

Instead of using the index of a column, you can also locate a value using the variable name of its column. To do this, you can use the following syntax of the DataRow indexed property:

public object this[DataColumn column] {get; set;}

This property expects the object name of the column passed in its square brackets. The third option you have is to identify the column by its index. To do this, use the following syntax of the DataRow indexed property:

public object this[int columnIndex] {get; set;}

This property expects the index of the column.
 

Practical Learning Practical Learning: Locating a Value in a Record and Updating it
  1. To locate a value inside a record, change the DoubleClick events of the list view as follows:
      
    private void lvwPeople_DoubleClick(object sender, System.EventArgs e)
{
	ListViewItem selPerson = this.lvwPeople.SelectedItems[0];
	int indexOfPersonSelected = selPerson.Index;
DataRow rowPerson = this.tblPersons.Rows[indexOfPersonSelected];NewPerson dlgPerson = new NewPerson();

	dlgPerson.txtFullName.Text = (string)(rowPerson["FullName"]);
	dlgPerson.txtFriendlyName.Text = (string)(rowPerson["FriendlyName"]);
	dlgPerson.cboGenders.Text = (string)(rowPerson["Gender"]);
	dlgPerson.cboRelationships.Text = (string)(rowPerson["TypeOfRelationship"]);
	dlgPerson.txtKnownSince.Text = (string)(rowPerson["KnownSince"]);
	dlgPerson.txtResidence.Text = (string)(rowPerson["CurrentResidence"]);
	dlgPerson.txtPhoneNumber.Text = (string)(rowPerson["PhoneNumber"]);
	dlgPerson.dtpLastUpdate.Text = (string)(rowPerson["LastUpdate"]);

	string strNotify = (string)(rowPerson["NotifyIfEmergency"]);
	bool bNotity = false;

	if( strNotify == "true" )
		bNotity = true;

	dlgPerson.chkNotify.Checked = bNotity;
	dlgPerson.btnCreate.Text = "Update";

	if( dlgPerson.ShowDialog() == DialogResult.OK )
	{
		rowPerson["FullName"] = dlgPerson.txtFullName.Text;
		rowPerson["FriendlyName"] = dlgPerson.txtFriendlyName.Text;
		rowPerson["Gender"] = dlgPerson.cboGenders.Text;
		rowPerson["TypeOfRelationship"] = dlgPerson.cboRelationships.Text;
		rowPerson["KnownSince"] = dlgPerson.txtKnownSince.Text;
		rowPerson["CurrentResidence"] = dlgPerson.txtResidence.Text;
		rowPerson["PhoneNumber"] = dlgPerson.txtPhoneNumber.Text;
		rowPerson["LastUpdate"] = dlgPerson.dtpLastUpdate.Value.ToString("d");
		rowPerson["NotifyIfEmergency"] = dlgPerson.chkNotify.Checked.ToString();

		this.dsAddressBook.WriteXml("PeopleInMyLife.xml");
		RefreshPeople();
	}
}
  2. Return to the form. Under the form, click contextMenu1
  3. On the form, click Context Menu and click Edit Details
  4. In the Events section of the Properties window, set the Click event to lvwPeople_DoubleClick
  5. Execute the application
  6. In the list view, double-click a record, change some of its values and

Record Maintenance

Once a table has been filled with records, you can perform maintenance operations on it such as changing some records or removing others. To remove a record from a table, you can call the DataRowCollection.Remove() method. Its syntax is:

public void Remove(DataRow row);

This method takes as argument a DataRow object and checks whether the table contains it. If that record exists, it gets deleted, including all of its entries for each column. When calling this method, you must pass an exact identification of the record. If you don't have that identification, you can delete a record based on its index. To do this, you would call the DataRowCollection.RemoveAt() method. Its syntax is:

public void RemoveAt(int index);

This method takes as argument the index of the record you want to delete. If a record with that index exists, it would be deleted.

To delete all records of a table, call the DataRowCollection.Clear() method. Its syntax is:

public void Clear();

This method is used to clear the table of all records.
 

Practical Learning Practical Learning: Deleting Records
  1. Display the first form. Under the form, click contextMenu1
  2. On the form, click Context Menu and double-click Delete Person
  3. Implement the event as follows:
      
    private void mnuDeletePerson_Click(object sender, System.EventArgs e)
{
	ListViewItem selPerson = this.lvwPeople.SelectedItems[0];
	int indexOfPersonSelected = selPerson.Index;

	if( indexOfPersonSelected >= 0 )
	{
		DataRow rowPerson = this.tblPersons.Rows[indexOfPersonSelected];
		System.Windows.Forms.DialogResult answer = 
			MessageBox.Show("Are you sure you want to delete this record?",
			"Deleting a Record",
			MessageBoxButtons.YesNo,
			MessageBoxIcon.Information);
		if( answer == DialogResult.Yes )
		{
			this.tblPersons.Rows.Remove(rowPerson);
			this.dsAddressBook.WriteXml(this.strFilename);
		}
		RefreshPeople();
	}
}
  4. Return to the form and double-click the Remove all People menu item
  5. Implement the event as follows:
      
    private void mnuRemoveAll_Click(object sender, System.EventArgs e)
{
	System.Windows.Forms.DialogResult answer = 
		MessageBox.Show("Are you sure you want to delete all records?",
		"Deleting all Record",
		MessageBoxButtons.YesNo,
		MessageBoxIcon.Information);
	if( answer == DialogResult.Yes )
	{
		this.tblPersons.Rows.Clear();
		this.dsAddressBook.WriteXml(this.strFilename);
	}
	RefreshPeople();
}
  6. Execute the application
  7. Close the form(s)
 
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