Columns Maintenance
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Columns Maintenance |
Column maintenance consists of adding one or more columns to a table, identifying an existing column in a table, looking for a column in a table, deleting one column or deleting all columns of a table. All these operations are easily supported by the various classes of the System.Data namespace.
You are probably now familiar with the relationships among the data set, the table and the columns. Just in case:
When using the information stored in a table we will learn when studying records, sometimes you will need to identify the table that owns a particular column you are accessing. This information can be provided by the Table property of the DataColumn class.
Once again, remember that the group of columns of a table is an object of type DataColumnCollection. The DataColumnCollection class implements the GetEnumerator() method of the IEnumerable interface. This allows you to enumerate the columns of a table using foreach. |
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using System;
using System.Data;
namespace VideoCollection2
{
public class Video
{
private DataSet dsVideoCollection;
private DataColumn colActorName;
private DataColumn colDateOfBirth;
private DataTable tblActors;
private DataColumn colTitle;
private DataColumn colDirector;
private DataColumn colLength;
private DataColumn colFormat;
private DataColumn colRating;
private DataTable tblVideos;
public Video()
{
dsVideoCollection = new DataSet("VideoCollection");
tblActors = new DataTable("Actors");
colActorName = new DataColumn();
colActorName.ColumnName = "Actor Name";
colActorName.DataType = Type.GetType("System.String");
tblActors.Columns.Add(colActorName);
colDateOfBirth = new DataColumn("Date of Birth",
Type.GetType("System.DateTime"));
tblActors.Columns.Add(colDateOfBirth);
dsVideoCollection.Tables.Add(tblActors);
tblVideos = new DataTable("Videos");
colTitle = new DataColumn("Title", Type.GetType("System.String"));
tblVideos.Columns.Add(colTitle);
colDirector = new DataColumn("Director",
Type.GetType("System.String"));
tblVideos.Columns.Add(colDirector);
colLength = new DataColumn("Length",
Type.GetType("System.String"));
tblVideos.Columns.Add(colLength);
colFormat = new DataColumn("Format",
Type.GetType("System.Int16"));
tblVideos.Columns.Add(colFormat);
colRating = new DataColumn("Rating",
Type.GetType("System.Byte"));
tblVideos.Columns.Add(colRating);
dsVideoCollection.Tables.Add(tblVideos);
}
public void ShowTables()
{
int i = 1;
Console.WriteLine("=-=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console.WriteLine("Video Collection - Tables");
Console.WriteLine("=-=-=-=-=-=-=-=-=-=-=-=-=-=-=");
foreach (DataTable tbl in dsVideoCollection.Tables)
Console.WriteLine("{0}. {1}", i++, tbl.TableName);
Console.WriteLine("----------------------------");
}
public void ShowColumns(string table)
{
int i = 1;
DataTable tbl = dsVideoCollection.Tables[table];
Console.WriteLine("=-=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console.WriteLine("Video Collection - {0} Columns", table);
Console.WriteLine("=-=-=-=-=-=-=-=-=-=-=-=-=-=-=");
foreach (DataColumn col in tbl.Columns)
Console.WriteLine("{0}. {1}", i++, col.ColumnName);
Console.WriteLine("----------------------------");
}
}
}
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using System;
namespace VideoCollection2
{
public class Program
{
static int Main(string[] args)
{
char answer = 'q';
char choiceTable = '0';
Video vdo = new Video();
do
{
try
{
Console.WriteLine("\nWhat do you want to do?");
Console.WriteLine("1. Show the tables");
Console.WriteLine("2. Show the columns of a table");
Console.WriteLine("0. Quit");
Console.Write("Your Choice: ");
answer = char.Parse(Console.ReadLine());
Console.WriteLine("=========================\n");
}
catch (FormatException)
{
Console.WriteLine("Invalid Choice!");
}
switch (answer)
{
case '1':
vdo.ShowTables();
break;
case '2':
Console.WriteLine("Here are the available tables");
vdo.ShowTables();
try
{
Console.Write("Enter the table whose columns you want to review: ");
choiceTable = char.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("Invalid answer!");
}
if (choiceTable == '1')
vdo.ShowColumns("Actors");
else if (choiceTable == '2')
vdo.ShowColumns("Videos");
break;
default:
break;
}
} while((answer == '1') ||
(answer == '2'));
return 0;
}
}
}
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What do you want to do? 1. Show the tables 2. Show the columns of a table 0. Quit Your Choice: 1 ========================= =-=-=-=-=-=-=-=-=-=-=-=-=-=-= Video Collection - Tables =-=-=-=-=-=-=-=-=-=-=-=-=-=-= 1. Actors 2. Videos ---------------------------- What do you want to do? 1. Show the tables 2. Show the columns of a table 0. Quit Your Choice: 2 ========================= Here are the available tables =-=-=-=-=-=-=-=-=-=-=-=-=-=-= Video Collection - Tables =-=-=-=-=-=-=-=-=-=-=-=-=-=-= 1. Actors 2. Videos ---------------------------- Enter the table whose columns you want to review: 2 =-=-=-=-=-=-=-=-=-=-=-=-=-=-= Video Collection - Videos Columns =-=-=-=-=-=-=-=-=-=-=-=-=-=-= 1. Title 2. Director 3. Length 4. Format 5. Rating ---------------------------- What do you want to do? 1. Show the tables 2. Show the columns of a table 0. Quit Your Choice: 0 ========================= Press any key to continue . . . |
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Practical Learning: Listing the Columns of a table