/// <summary>
/// Problem solved by only using 1 db connection or introducing transactions isolation levels
/// </summary>
public static void Main()
{
using (var db1 = new NorthwindEntities())
{
using (var db2 = new NorthwindEntities())
{
Console.WriteLine("First connection altering");
Console.WriteLine("Original -> " + db1.Employees.First().City);
db1.Employees.First().City = "Changed city";
Console.WriteLine("Changed -> " + db1.Employees.First().City);
Console.WriteLine("Second connection altering");
Console.WriteLine("Original -> " + db2.Employees.First().City);
db2.Employees.First().City = "Altered city";
Console.WriteLine("Changed -> " + db2.Employees.First().City);
db1.SaveChanges();
db2.SaveChanges();
}
}
using (var db3 = new NorthwindEntities())
{
Console.WriteLine("Final connection altering");
Console.WriteLine(db3.Employees.First().City);
}
}
public static string AddCustomer(NorthwindEntities northwind, Customer customer)
{
northwind.Customers.Add(customer);
northwind.SaveChanges();
return "Customer added";
}
public static void Main()
{
using (var northwind1 = new NorthwindEntities())
{
TransactionOptions options = new TransactionOptions();
options.IsolationLevel = IsolationLevel.Serializable;
using (var scope = new TransactionScope(TransactionScopeOption.Required, options))
{
using (var northwind2 = new NorthwindEntities())
{
Customer customer = northwind1.Customers.FirstOrDefault();
customer.Country = "NewCountry";
Customer customer2 = northwind2.Customers.FirstOrDefault();
northwind1.SaveChanges();
Console.WriteLine("First connection country ->" + customer.Country);
Console.WriteLine("Second connection country ->" + customer2.Country);
Console.WriteLine("The second connection works with the old data - dirty read.");
scope.Complete();
}
}
}
}
public static string DeleteCustomer(NorthwindEntities northwind, Customer newCustomer)
{
var selectedCustomer = northwind.Customers.Where(c => c.CustomerID == newCustomer.CustomerID).FirstOrDefault();
northwind.Customers.Remove(selectedCustomer);
northwind.SaveChanges();
return "Customer deleted";
}
/// <summary>
/// EF works with transactions by default - calling SaveChanges() starts a transaction by default.
/// However we can use transactions to unify many calling of SaveChanges() as one and if one fails - all fail.
/// </summary>
public static void Main()
{
using (var db = new NorthwindEntities())
{
using (var transaction = db.Database.BeginTransaction())
{
var order = new Order()
{
CustomerID = "WELLI",
EmployeeID = 4
};
db.Orders.Add(order);
var orderDetails1 = new Order_Detail()
{
OrderID = order.OrderID,
ProductID = 5,
UnitPrice = 12.34m,
Quantity = 100,
Discount = 0.2f
};
var orderDetails2 = new Order_Detail()
{
OrderID = order.OrderID,
ProductID = 3,
UnitPrice = 12.34m,
Quantity = 100,
Discount = 0.2f
};
var orderDetails3 = new Order_Detail()
{
OrderID = order.OrderID,
ProductID = 4,
UnitPrice = 12.34m,
Quantity = 100,
Discount = 0.2f
};
db.Order_Details.AddRange(new[] { orderDetails1, orderDetails2, orderDetails3 });
try
{
db.SaveChanges();
}
catch (System.Exception ex)
{
System.Console.WriteLine(ex);
transaction.Rollback();
}
transaction.Commit();
}
}
}
public static int ModifyCustomer(string contactName, string companyName)
{
using (NorthwindEntities db = new NorthwindEntities())
{
string id = GetCustomerId(companyName);
var customer = db.Customers.Where(x => x.CustomerID == id).FirstOrDefault();
if (customer == null) throw new ArgumentException("The record you are trying to modify doesn't exist!!!");
customer.CompanyName = companyName;
customer.ContactName = contactName;
return db.SaveChanges();
}
}
public static int DeleteCustomer(string companyName)
{
using (NorthwindEntities db = new NorthwindEntities())
{
string id = GetCustomerId(companyName);
if (IsCustomerExists(db, id))
{
Customer customer = db.Customers.Where(x => x.CustomerID == id).FirstOrDefault();
db.Customers.Remove(customer);
return db.SaveChanges();
}
else
{
return 0;
}
}
}
public static void Main()
{
using (var northwind = new NorthwindEntities())
{
using (var scope = new TransactionScope())
{
for (int i = 0; i < 10; i++)
{
northwind.Orders.Add(new Order() { ShipAddress = "455, Metropolitan Avenue" });
}
northwind.SaveChanges();
scope.Complete();
}
Console.WriteLine("Number of added orders: {0}", northwind.Orders.Where(o => o.ShipAddress == "455, Metropolitan Avenue").Count());
}
}
public static int InsertCustomer(string contactName, string companyName)
{
using (NorthwindEntities db = new NorthwindEntities())
{
Customer customer = new Customer()
{
ContactName = contactName,
CompanyName = companyName,
CustomerID = GetCustomerId(companyName),
};
if (IsCustomerExists(db, GetCustomerId(companyName)))
{
throw new ArgumentException("Customer already exist!!!");
}
db.Customers.Add(customer);
return db.SaveChanges();
}
}
public static string ModifyCustomerById(NorthwindEntities northwind, string customerId, Customer newCustomer)
{
var selectedCustomer = northwind.Customers.Where(c => c.CustomerID == customerId).FirstOrDefault();
selectedCustomer.Address = newCustomer.Address;
selectedCustomer.City = newCustomer.City;
selectedCustomer.CompanyName = newCustomer.CompanyName;
selectedCustomer.ContactName = newCustomer.ContactName;
selectedCustomer.ContactTitle = newCustomer.ContactTitle;
selectedCustomer.Country = newCustomer.Country;
selectedCustomer.CustomerDemographics = newCustomer.CustomerDemographics;
selectedCustomer.Fax = newCustomer.Fax;
selectedCustomer.Orders = newCustomer.Orders;
selectedCustomer.Phone = newCustomer.Phone;
selectedCustomer.PostalCode = newCustomer.PostalCode;
selectedCustomer.Region = newCustomer.Region;
northwind.SaveChanges();
return "Customer modified";
}
//TODO: Try to open two different data contexts and perform concurrent changes on the same records.
// What will happen at SaveChanges()? How to deal with it?
static void Main()
{
string companyName = "Concurency Test";
string contactName = "Concurent1";
string contactName2 = "Concurent2";
using (NorthwindEntities db = new NorthwindEntities())
{
using(NorthwindEntities db2 = new NorthwindEntities())
{
string id = GetCustomerId(companyName);
var customer = db.Customers.Where(x => x.CustomerID == id).FirstOrDefault();
var customer2 = db2.Customers.Where(x => x.CustomerID == id).FirstOrDefault();
if (customer == null) throw new ArgumentException("The record you are trying to modify doesn't exist!!!");
customer.CompanyName = companyName;
customer.ContactName = contactName;
customer2.ContactName= contactName2;
db.SaveChanges();
db2.SaveChanges();
}
}
}
private static void CreateOrder(Order newOrder, int numberOfRepeatsUntillSuccess)
{
bool isTransactionSucceed = false;
using (NorthwindEntities dbContext = new NorthwindEntities())
{
using (TransactionScope transaction = new TransactionScope())
{
for (int i = 0; i < numberOfRepeatsUntillSuccess; i++)
{
try
{
dbContext.Orders.Add(newOrder);
dbContext.SaveChanges();
transaction.Complete();
isTransactionSucceed = true;
break;
}
catch (UpdateException ex)
{
if (i == numberOfRepeatsUntillSuccess - 1)
{
throw new InvalidOperationException("Cannot complete order creation", ex);
}
}
}
if (isTransactionSucceed)
{
// Reset the context since the operation succeeded.
Console.WriteLine("Transaction sompited");
}
else
{
Console.WriteLine("The operation could not be completed in "
+ numberOfRepeatsUntillSuccess + " tries.");
}
}
}
}
public static void AddOrder(NorthwindEntities northwind, Order order)
{
northwind.Orders.Add(order);
northwind.SaveChanges();
}
