public static void DeleteCustomer(string customerID)
{
using (var db = new NorthwindEntities())
{
var customer = db.Customers
.FirstOrDefault(c => c.CustomerID == customerID);
db.Customers.Remove(customer);
db.SaveChanges();
}
}
public static void ModifyCustomer(string customerID, string contactName, string companyName, string address)
{
var db = new NorthwindEntities();
using (db)
{
var customer = db.Customers
.FirstOrDefault(c => c.CustomerID == customerID);
customer.ContactName = contactName;
customer.CompanyName = companyName;
customer.Address = address;
db.SaveChanges();
}
}
public static string InsertCustomer(Customer customer)
{
if (customer == null)
{
throw new ArgumentNullException("The customer can't be null");
}
else
{
var db = new NorthwindEntities();
using (db)
{
db.Customers.Add(customer);
db.SaveChanges();
}
return customer.CustomerID;
}
}
static void Main()
{
//Try to open two different data contexts and perform concurrent changes
//on the same records. What will happen at SaveChanges()? - it will going to update
//the record two times first to "Ihu" than to "Bla"
//How to deal with it? - use only one connection
var db1 = new NorthwindEntities();
var db2 = new NorthwindEntities();
Customer customer1 = db1.Customers.FirstOrDefault(c => c.CustomerID == "A");
Customer customer2 = db2.Customers.FirstOrDefault(c => c.CustomerID == "A");
customer1.ContactName = "Ihu";
customer2.ContactName = "Bla";
db1.SaveChanges();
db2.SaveChanges();
}
private static void InsertOrderUsingExternalTransaction(NorthwindEntities db, Order order)
{
using (db)
{
using(var transaction = db.Database.BeginTransaction())
{
try
{
db.Orders.Add(order);
db.SaveChanges();
transaction.Commit();
}
catch (Exception ex)
{
Console.WriteLine("Can't insert record", ex.Message);
transaction.Rollback();
}
}
}
}