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Using C# Classes to Create a Database

In this lesson, we will be using classes and List<> to create an example database to manage employees. We will create a menu system that will allow us to Create, Read, Uupdate, and Delete employees from this List.

Reviewing the starting code.

We will make a new project: dotnet new sdg-console -o SuncoastHumanResources

The code below is our starting point. It defines an Employee class and contains code to input the details of a single employee.

using System;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
var employee = new Employee();
DisplayGreeting();
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
Console.WriteLine($"Hello, {employee.Name} you make {employee.MonthlySalary()} dollars per month.");
}
}
}

While this is a good start, it lacks features. Most significantly, we can only store one employee, so our Employee Database is not very useful. To improve it, let's add a menu system to prompt the user to add, search, and delete employees. We will keep all these employees in a List and use classes to organize our code.

Adding a List to store our employees

The List we will create will look like this:

var employees = new List<Employee>();

We name the variable employees, the plural of employee to hint that this variable stores a collection of things. While this isn't a mandate by the language, choosing good names for our variables is a quality of a good developer and a habit we should start early. We define this variable as a List of things that will all be instances of our Employee class.

To put an employee in our list, we use the code: employees.Add(employee) where employee is an instance of Employee

Now our code looks like this:

using System;
using System.Collections.Generic;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
var employees = new List<Employee>();
var employee = new Employee();
DisplayGreeting();
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
employees.Add(employee);
}
}
}

Let's make a simple menu

To make a menu, we'll introduce a keepGoing variable which will track if the user wishes to continue in our program. We will use this variable in a while loop to determine when to stop the loop. Inside the loop, we will show a prompt and use the existing code to ask the user for details on a new employee.

The menu allows the user to add employees to our list until they select the option to quit.

using System;
using System.Collections.Generic;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
// Our list of employees
var employees = new List<Employee>();
DisplayGreeting();
// Should we keep showing the menu?
var keepGoing = true;
// While the user hasn't said QUIT yet
while (keepGoing) {
// Insert a blank line then prompt them and get their answer (force uppercase)
Console.WriteLine();
Console.Write("What do you want to do? (A)dd an employee or (Q)uit: ");
var choice = Console.ReadLine().ToUpper();
if (choice == "Q") {
// They said quit, so set our keepGoing to false
keepGoing = false;
} else {
// Make a new employee object
var employee = new Employee();
// Prompt for values and save them in the employee's properties
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
// Add it to the list
employees.Add(employee);
}
// end of the `while` statement
}
}
}
}

Add an option to show all the employees

Let's add a menu item to show all the employees in the database.

using System;
using System.Collections.Generic;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
// Our list of employees
var employees = new List<Employee>();
// Should we keep showing the menu?
var keepGoing = true;
DisplayGreeting();
// While the user hasn't said QUIT yet
while (keepGoing) {
// Insert a blank line then prompt them and get their answer (force uppercase)
Console.WriteLine();
Console.Write("What do you want to do? (A)dd an employee or (S)how all the employees or (Q)uit: ");
var choice = Console.ReadLine().ToUpper();
if (choice == "Q") {
// They said quit, so set our keepGoing to false
keepGoing = false;
} else if (choice == "S") {
// Loop through each employee
foreach(var employee in employees) {
// And print details
Console.WriteLine($"{employee.Name} is in department {employee.Department} and makes ${employee.Salary}");
}
} else {
// Make a new employee object
var employee = new Employee();
// Prompt for values and save them in the employee's properties
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
// Add it to the list
employees.Add(employee);
}
// end of the `while` statement
}
}
}
}

Find an employee by name

Adding another menu option to find an employee by name. First, we prompt for the name to search. We use a foreach loop to look for an employee with a matching name. If we find one, we update a variable named foundEmployee which otherwise will have the value null. After the loop is done if foundEmployee is null, we show the user a message; otherwise, we display the details of foundEmployee.

using System;
using System.Collections.Generic;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
// Our list of employees
var employees = new List<Employee>();
// Should we keep showing the menu?
var keepGoing = true;
DisplayGreeting();
// While the user hasn't said QUIT yet
while (keepGoing) {
// Insert a blank line then prompt them and get their answer (force uppercase)
Console.WriteLine();
Console.Write("What do you want to do? (A)dd an employee or (S)how all the employees or (F)ind an employee or (Q)uit: ");
var choice = Console.ReadLine().ToUpper();
if (choice == "Q") {
// They said quit, so set our keepGoing to false
keepGoing = false;
} else if (choice == "F") {
// Ask for the name of an employee
var name = PromptForString("What name are you looking for? ");
// Make a new variable to store the found employee, initializing
// to null which will indicate no match found
Employee foundEmployee = null;
// Go through all the employees
foreach(var employee in employees) {
// If the name matches
if (employee.Name == name) {
// ... then store this employee in the foundEmployee variable
foundEmployee = employee;
}
}
// If the foundEmployee is still null, nothing was found
if (foundEmployee == null) {
Console.WriteLine("No match found");
} else {
// Otherwise print details of the found employee
Console.WriteLine($"{foundEmployee.Name} is in department {foundEmployee.Department} and makes ${foundEmployee.Salary}");
}
} else if (choice == "S") {
// Loop through each employee
foreach(var employee in employees) {
// And print details
Console.WriteLine($"{employee.Name} is in department {employee.Department} and makes ${employee.Salary}");
}
} else {
// Make a new employee object
var employee = new Employee();
// Prompt for values and save them in the employee's properties
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
// Add it to the list
employees.Add(employee);
}
// end of the `while` statement
}
}
}
}

Improving this code by adding LINQ

We can add using System.Linq to the top of our code, then we can utilize FirstOrDefault for our searching code.

// Ask for the name of an employee
var name = PromptForString("What name are you looking for: ");
// Make a new variable to store the found employee, initializing
// to null, which will indicate no match found
Employee foundEmployee = employees.FirstOrDefault(employee => employee.Name == name);
// If the foundEmployee is still null, nothing was found
if (foundEmployee == null) {
Console.WriteLine("No match found");
} else {
// Otherwise print details of the found employee
Console.WriteLine($"{foundEmployee.Name} is in department {foundEmployee.Department} and makes ${foundEmployee.Salary}");
}

Delete an employee and update an employee

These are two other features that our employee database might need. We'll leave these to you to add to the application if you'd like to try.

Refactoring the database features into a class

The functions for adding, searching, and displaying all the employees from the list exist in the main code. Extracting the code into a specific class to manage the list will increase the code's clarity and give specific places to implement new features.

We start by creating a class EmployeeDatabase and move our List<Employee> inside. We make this class property private since we do not want code outside of the class to access it. All the usage must come from the methods we create and allow as public. We then develop methods to perform the common actions we need, GetAllEmployees, FindOneEmployee, AddEmployee. Each of these methods receives data it needs and returns the data it provides. These methods essentially create an API (Application Programming Interface) for how to use this code.

By creating a class EmployeeDatabase, we have isolated the code that has to do with the list of employees. The organization of the class allows the database implementation to change without modifying the code that uses it. For instance, we could load and save the data from a data file. Any time we can change one part of the system, for example, the employee database, without changing other parts of the code, for example, the menu system, we have created a good decoupling of our system's components.

using System;
using System.Collections.Generic;
namespace SuncoastHumanResources
{
class Employee
{
public string Name { get; set; }
public int Department { get; set; }
public int Salary { get; set; }
public int MonthlySalary()
{
return Salary / 12;
}
}
class EmployeeDatabase
{
// Keep a *private* copy of the employee list.
//
// We make this private since we don't want code from
// outside this class to have access to it. All access
// to this information comes through the methods of the
// class.
private List<Employee> employees = new List<Employee>();
// Get a list of all the employees
public List<Employee> GetAllEmployees()
{
return employees;
}
// Given an argument of an employee, add that employee
// to the list of employees we are managing.
public void AddEmployee(Employee newEmployee)
{
employees.Add(newEmployee);
}
// Given a name as a string, look through the list of
// employees. If we find one with a matching name, return
// the employee. If nothing is found, return a null.
public Employee FindOneEmployee(string name)
{
// to null which will indicate no match found
Employee foundEmployee = employees.FirstOrDefault(employee => employee.Name == name)
// Return what we found (the employee or null)
return foundEmployee;
}
}
class Program
{
static void DisplayGreeting()
{
Console.WriteLine("----------------------------------------");
Console.WriteLine(" Welcome to Our Employee Database ");
Console.WriteLine("----------------------------------------");
Console.WriteLine();
Console.WriteLine();
}
static string PromptForString(string prompt)
{
Console.Write(prompt);
var userInput = Console.ReadLine();
return userInput;
}
static int PromptForInteger(string prompt)
{
Console.Write(prompt);
int userInput;
var isThisGoodInput = Int32.TryParse(Console.ReadLine(), out userInput);
if (isThisGoodInput)
{
return userInput;
}
else
{
Console.WriteLine("Sorry, that isn't a valid input, I'm using 0 as your answer.");
return 0;
}
}
static void Main(string[] args)
{
// Our database
var database = new EmployeeDatabase();
// Should we keep showing the menu?
var keepGoing = true;
DisplayGreeting();
// While the user hasn't said QUIT yet
while (keepGoing) {
// Insert a blank line then prompt them and get their answer (force uppercase)
Console.WriteLine();
Console.Write("What do you want to do? (A)dd an employee or (S)how all the employees or (F)ind an employee or (Q)uit: ");
var choice = Console.ReadLine().ToUpper();
if (choice == "Q") {
// They said quit, so set our keepGoing to false
keepGoing = false;
} else if (choice == "F") {
// Ask for the name of an employee
var name = PromptForString("What name are you looking for? ");
// Make a new variable to store the found employee, or null if not found
Employee foundEmployee = database.FindOneEmployee(name);
// If the foundEmployee is still null, nothing was found
if (foundEmployee == null) {
Console.WriteLine("No match found");
} else {
// Otherwise print details of the found employee
Console.WriteLine($"{foundEmployee.Name} is in department {foundEmployee.Department} and makes ${foundEmployee.Salary}");
}
} else if (choice == "S") {
var employees = database.GetAllEmployees();
// Loop through each employee
foreach(var employee in employees) {
// And print details
Console.WriteLine($"{employee.Name} is in department {employee.Department} and makes ${employee.Salary}");
}
} else {
// Make a new employee object
var employee = new Employee();
// Prompt for values and save them in the employee's properties
employee.Name = PromptForString("What is your name? ");
employee.Department = PromptForInteger("What is your department number? ");
employee.Salary = PromptForInteger("What is your yearly salary (in dollars)? ");
// Add it to the list
database.AddEmployee(employee);
}
// end of the `while` statement
}
}
}
}
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