Introduction
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A list used in a LINQ statement can be made of any type
of value (numbers, strings, etc), as long as the values are of the same
type.
Here is an example: |
using System;
using System.Linq;
public class Exercise
{
public static int Main()
{
var names = new string[5];
names[0] = "Patricia Katts";
names[1] = "Raymond Kouma";
names[2] = "Hél�ne Mukoko";
names[3] = "Paul Bertrand Yamaguchi";
names[4] = "Gertrude Monay";
var name = from n
in names
select n;
foreach (var member in name)
Console.WriteLine("Member: {0}", member.ToString());
return 0;
}
}
This would produce:
The values used in a LINQ statement can also come from a class. For example, instead of using one of the primitive types to create a list, you can use your own class.
Here is an example:
public class Employee
{
public int EmployeeNumber;
public string FirstName;
public string LastName;
public double HourlySalary;
}
You primarily use the class as you would any other. In your LINQ statement, you can refer to all members of the collection:
using System;
using System.Linq;
public class Employee
{
public int EmployeeNumber;
public string FirstName;
public string LastName;
public double HourlySalary;
}
public class Exercise
{
public static int Main()
{
var empls = new Employee[5];
empls[0] = new Employee();
empls[0].EmployeeNumber = 971974;
empls[0].FirstName = "Patricia";
empls[0].LastName = "Katts";
empls[0].HourlySalary = 24.68;
empls[1] = new Employee();
empls[1].EmployeeNumber = 208411;
empls[1].FirstName = "Raymond";
empls[1].LastName = "Kouma";
empls[1].HourlySalary = 20.15;
empls[2] = new Employee();
empls[2].EmployeeNumber = 279374;
empls[2].FirstName = "Hél�ne";
empls[2].LastName = "Mukoko";
empls[2].HourlySalary = 15.55;
empls[3] = new Employee();
empls[3].EmployeeNumber = 707912;
empls[3].FirstName = "Bertrand";
empls[3].LastName = "Yamaguchi";
empls[3].HourlySalary = 24.68;
empls[4] = new Employee();
empls[4].EmployeeNumber = 971394;
empls[4].FirstName = "Gertrude";
empls[4].LastName = "Monay";
empls[4].HourlySalary = 20.55;
var staff = from n in empls select n;
return 0;
}
}
In this case, the value of the select expression represents the whole variable, which are all members of the collection. If you want to get a property (or a member) of the class, apply the period operator to the value of select and access the desired member.
Here is an example:
using System;
using System.Linq;
public class Employee
{
public int EmployeeNumber;
public string FirstName;
public string LastName;
public double HourlySalary;
}
public class Exercise
{
public static int Main()
{
var empls = new Employee[5];
. . . No Change
var lastNames = from n
in empls
select n.LastName;
foreach (var member in lastNames)
Console.WriteLine("Member: {0}", member.ToString());
return 0;
}
}
This would produce:
This technique allows you to access only one member of the class.
As mentioned already, the select
statement primarily produces the whole collection of the values of the
variable. Since this value represents a collection, you can use it in a
list-based such scenario. In this case, to access a member of the class, use
a for or foreach loop to get each item of
the collection variable and apply the period operator on that value.
 Practical
Learning: Creating a Query |
- Change the Load event as follows:
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.IO; using System.Runtime.Serialization.Formatters.Binary; namespace AltairRealtors1 { public class AltairRealtors { static Property[] lstProperties; public static int Main(string[] args) { FileStream stmProperties = null; BinaryFormatter bfmProperties = new BinaryFormatter(); // This is the file that holds the list of properties string Filename = @"C:\Altair Realtors\Properties.atr"; // Find out if there is already a file that contains a list of properties. // If that file exists, open it. if (File.Exists(Filename)) { stmProperties = new FileStream(Filename, FileMode.Open, FileAccess.Read, FileShare.Read); try { // Retrieve the list of items from file lstProperties = (Property[])bfmProperties.Deserialize(stmProperties); var numbers = from iNumbers in lstProperties select iNumbers.PropertyNumber; int i = 0; Console.WriteLine(" # Prop #"); Console.WriteLine("-----------"); foreach (var nbr in numbers) { Console.WriteLine("{0,2}. {1}", (i + 1).ToString(), nbr); i++; } Console.WriteLine("=========="); } finally { stmProperties.Close(); } } return 0; } } } - Execute the application to see the result
- Close the DOS window and return to your programming environment
- Change the file as follows:
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.IO; using System.Runtime.Serialization.Formatters.Binary; namespace LINQ1 { public class AltairRealtors { static Property[] lstProperties; public static int Main(string[] args) { FileStream stmProperties = null; BinaryFormatter bfmProperties = new BinaryFormatter(); // This is the file that holds the list of properties string Filename = @"C:\Altair Realtors2\Properties.atr"; // Find out if there is already a file that contains a list of properties. // If that file exists, open it. if (File.Exists(Filename)) { stmProperties = new FileStream(Filename, FileMode.Open, FileAccess.Read, FileShare.Read); try { // Retrieve the list of items from file lstProperties = (Property[])bfmProperties.Deserialize(stmProperties); var properties = from props in lstProperties select props; int i = 1; Console.WriteLine("+===+========+==============+===============+=======+===========+======+=======+=======+======+===========+"); Console.WriteLine("| # | Prop # | Type | City | State | Condition | Beds | Baths |Stories| Year | Value |"); Console.WriteLine("+===+========+==============+===============+=======+===========+======+=======+=======+======+===========+"); foreach (var prop in properties) { Console.WriteLine("| {0,2}| {1,-6} | {2,-12} | {3,-13} | {4,-4} | {5,-9} | {6,-3} | {7,-5} | {8,-4}| {9,-4} | {10,6} |", i, prop.PropertyNumber, prop.Type, prop.City, prop.State, prop.Condition, prop.Bedrooms, prop.Bathrooms.ToString("F"), prop.Stories, prop.YearBuilt, prop.MarketValue.ToString("F")); Console.WriteLine("+---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+"); i++; } } finally { stmProperties.Close(); } } return 0; } } } - Execute the application to see the result
+===+========+==============+===============+=======+===========+======+=======+=======+======+===========+ | # | Prop # | Type | City | State | Condition | Beds | Baths |Stories| Year | Value | +===+========+==============+===============+=======+===========+======+=======+=======+======+===========+ | 1| 524880 | SingleFamily | Silver Spring | MD | Good | 4 | 2.50 | 3 | 1995 | 495880.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 2| 688364 | SingleFamily | Alexandria | VA | Excellent | 4 | 3.50 | 2 | 2000 | 620724.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 3| 611464 | SingleFamily | Laurel | MD | Good | 1 | 0.00 | 2 | 0 | 422625.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 4| 749562 | Townhouse | Gettysburg | WV | Good | 3 | 2.50 | 3 | 2002 | 425400.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 5| 420115 | Unknown | Washington | DC | Unknown | 2 | 0.00 | 0 | 1982 | 312555.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 6| 200417 | Condominium | Germantown | MD | Excellent | 2 | 1.00 | 0 | 0 | 215495.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 7| 927474 | Townhouse | Arlington | VA | BadShape | 4 | 2.50 | 3 | 1992 | 415665.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 8| 682630 | SingleFamily | Martinsburg | WV | Good | 4 | 3.50 | 3 | 2005 | 325000.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 9| 288540 | Condominium | Silver Spring | MD | Good | 1 | 1.00 | 0 | 2000 | 242775.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 10| 247472 | SingleFamily | Silver Spring | MD | Excellent | 3 | 3.00 | 3 | 1996 | 625450.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 11| 297446 | Townhouse | Laurel | MD | Unknown | 4 | 1.50 | 2 | 2002 | 412885.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 12| 924792 | SingleFamily | Washington | DC | Good | 5 | 3.50 | 3 | 2000 | 555885.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 13| 294796 | SingleFamily | Falls Church | VA | Excellent | 5 | 2.50 | 2 | 1995 | 485995.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 14| 811155 | Condominium | Alexandria | VA | Good | 1 | 1.00 | 0 | 2000 | 352775.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 15| 447597 | Townhouse | Hyattsville | MD | Excellent | 3 | 2.00 | 3 | 1992 | 365880.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 16| 297415 | Townhouse | ashington | DC | Good | 4 | 3.50 | 1 | 2004 | 735475.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 17| 475974 | SingleFamily | Gaithersburg | MD | Unknown | 4 | 2.50 | 1 | 1965 | 615775.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 18| 927409 | Condominium | McLean | VA | Excellent | 1 | 1.00 | 12 | 2006 | 485900.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 19| 304750 | Condominium | Washington | DC | Unknown | 2 | 2.00 | 6 | 1992 | 388665.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ | 20| 207850 | Townhouse | Rockville | MD | Good | 3 | 2.50 | 2 | 1988 | 525995.00 | +---+--------+--------------+---------------+-------+-----------+------+-------+-------+------+-----------+ Press any key to continue . . .
- Close the DOS window and return to your programming environment
Using a Method
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To perform a more particular operation on a class, you can create a method in it and then call that method in your LINQ statement. This means that, just as you can access a field or a property of a class, you can access any of its internal or public methods. Here is an example of a method created in a class:
using System;
using System.Linq;
public class Employee
{
public int EmployeeNumber;
public string FirstName;
public string LastName;
public double HourlySalary;
public Employee(int number = 0,
string firstName = "John",
string lastName = "Doe",
double salary = 0D)
{
EmployeeNumber = number;
FirstName = firstName;
LastName = lastName;
HourlySalary = salary;
}
internal string GetFullName()
{
return LastName +
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