static void Main()
{
var context = new NewsDBContext();
var data = context.News.Find(1);
//WARNING: Concurency handling should be tested by running two instances of the app.
while (true)
{
try
{
data.Content = Console.ReadLine();
context.SaveChanges();
Console.WriteLine("Changes successfully saved in the DB.");
break;
}
catch (DbUpdateConcurrencyException exc)
{
exc.Entries.Single().Reload();
Console.WriteLine("Conflict! Text from DB:" + context.News.Find(1).Content
+ ". Enter the corrected text:");
}
}
}
private static void CorrectNewsContent()
{
using (var db = new NewsDBContext())
{
var news = db.News.ToList();
var first = news.First();
Console.WriteLine("Text from DB: {0}", first.Content);
Console.WriteLine("Enter the corrected text: ");
string input = Console.ReadLine();
first.Content = input;
try
{
db.SaveChanges();
Console.WriteLine("Changes successfully saved in the DB.");
}
catch (DbUpdateConcurrencyException)
{
Console.WriteLine("Conflict!");
CorrectNewsContent();
}
}
}
private static void ConcurrencyFirstWins()
{
// The first user changes some record
var contextFirstUser = new NewsDBContext();
var newsFirstUser = contextFirstUser.Newses.Find(1);
Console.WriteLine("Text from DB: " + newsFirstUser.Content);
Console.Write("Enter the corrected text: ");
string newValueFirstUser = Console.ReadLine();
newsFirstUser.Content = newValueFirstUser;
// The second user changes the same record
var contextSecondUser = new NewsDBContext();
var newsSecondUser = contextSecondUser.Newses.Find(1);
Console.WriteLine("Text from DB: " + newsSecondUser.Content);
Console.Write("Enter the corrected text: ");
string newValueSecondUser = Console.ReadLine();
newsSecondUser.Content = newValueSecondUser;
// Conflicting changes: first wins; second gets an exception
contextFirstUser.SaveChanges();
try
{
contextSecondUser.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
Console.WriteLine("Conflict! Text from DB: " + newValueFirstUser);
Console.WriteLine(ex.Message);
}
}
static void Main()
{
var contextFirst = new NewsDBContext();
var lastNewFirstUer =
contextFirst.News.OrderByDescending(n => n.Id).First();
var contextSecondUser = new NewsDBContext();
var lastNewSecondUser =
contextSecondUser.News.OrderByDescending(n => n.Id).First();
Console.WriteLine("Application started.");
Console.WriteLine();
Console.WriteLine("First User.");
Console.WriteLine("Text from DB: " + lastNewFirstUer.ContentNews);
Console.Write("Enter the corrected text: ");
string firstUserInput = Console.ReadLine();
lastNewFirstUer.ContentNews = firstUserInput;
contextFirst.SaveChanges();
Console.WriteLine("Changes successfully saved in the DB.");
Console.WriteLine("Second User.");
Console.WriteLine("Text from DB: " + lastNewFirstUer.ContentNews);
Console.Write("Enter the corrected text: ");
string secondUserInput = Console.ReadLine();
lastNewSecondUser.ContentNews = secondUserInput;
try
{
contextSecondUser.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
Console.WriteLine("Conflict! Text from DB: " + lastNewFirstUer.ContentNews);
Console.WriteLine("Enter the corrected text: ");
string textAfterConflict = Console.ReadLine();
var newContext = new NewsDBContext();
var currNew =
contextSecondUser.News.OrderByDescending(n => n.Id).First();
currNew.ContentNews = textAfterConflict;
}
Console.WriteLine("Changes successfully saved in the DB.");
}
public static void ConcurrentUpdates()
{
// Problem 2.Concurrent Updates (Console App) -
// Step 1.At startup, the app should load from the DB the news text and print it on the console.
var firstContext = new NewsDBContext();
var firstConcurrentNews = firstContext.NewsItems.Find(1);
Console.WriteLine("Text from DB: " + firstConcurrentNews.Content + "\n");
// Step 2.After that, the app should enter a new value for the news text from the console.
Console.Write("User-1, Enter the corrected text: ");
firstConcurrentNews.Content = Console.ReadLine();
Console.WriteLine();
var secondContext = new NewsDBContext();
var secondConcurrentNews = secondContext.NewsItems.Find(1);
Console.Write("User-2, Enter the corrected text: ");
secondConcurrentNews.Content = Console.ReadLine();
Console.WriteLine();
// Step 3.After entering a new value, the app should try to save it to the DB.
// In case of success (no conflicting updates), the app should say
// that the changes were saved and should finish its work.
// In case of concurrent update conflict, the app should display
// an error message, should display the new (changed) text from the DB and should go to Step 2.
firstContext.SaveChanges(); // first user
Console.WriteLine(("Changes successfully saved in the DB.\n").ToUpper());
Console.WriteLine("Text from DB after first changes: " +
firstConcurrentNews.Content);
try
{
secondContext.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
Console.WriteLine("Concurrent Update Conflict!" + ex.Message);
Console.WriteLine("Text from DB: " +
firstConcurrentNews.Content +
"\n\nUser-2, Enter the corrected text:");
firstConcurrentNews.Content = Console.ReadLine();
Console.WriteLine(("\nChanges successfully saved in the DB.\n").ToUpper());
Console.WriteLine("Text from DB after second changes: " +
firstConcurrentNews.Content);
}
firstContext.SaveChanges();
}
private static void OptimisticConcurrencyLastWins()
{
// The first user changes some record
var contextFirstUser = new NewsDBContext();
var newsFirstUser = contextFirstUser.Newses.Find(1);
Console.WriteLine("Text from DB: " + newsFirstUser.Content);
Console.Write("Enter the corrected text: ");
string newValueFirstUser = Console.ReadLine();
newsFirstUser.Content = newValueFirstUser;
// The second user changes the same record
var contextSecondUser = new NewsDBContext();
var newsSecondUser = contextSecondUser.Newses.Find(1);
Console.WriteLine("Text from DB: " + newsSecondUser.Content);
Console.Write("Enter the corrected text: ");
string newValueSecondUser = Console.ReadLine();
newsSecondUser.Content = newValueSecondUser;
// Conflicting changes: last wins
contextFirstUser.SaveChanges();
contextSecondUser.SaveChanges();
Console.WriteLine("Changes successfully saved in the DB.");
}
static void Main()
{
Database.SetInitializer(new MigrateDatabaseToLatestVersion<NewsDBContext, Configuration>());
var context = new NewsDBContext();
//create database
var count = context.Newses.Count();
Console.WriteLine(count);
//Problem 2. Concurrent Updates
//Write a console app that edits the first news item in the DB. It should detect and handle any concurrent updates.
//Step 1. At startup, the app should load from the DB the news text and print it on the console.
//Step 2. After that, the app should enter a new value for the news text from the console.
//Step 3. After entering a new value, the app should try to save it to the DB.
//o In case of success (no conflicting updates), the app should say that the changes were saved and should finish its work.
//o In case of concurrent update conflict, the app should display an error message, should display the new (changed) text from the DB and should go to Step 2.
//Run simultaneously two instances of your app to simulate two concurrent users. Make an update conflict in the database and handle it.
//OptimisticConcurrencyLastWins();
ConcurrencyFirstWins();
}
private void Edit_OnLoaded(object sender, RoutedEventArgs e)
{
Context = new NewsDBContext();
Data = Context.News.Find(1);
}
