static void TestTables()
{
using (NorthwindEntities NWEntities = new NorthwindEntities())
{
// retrieve all Beverages products
IEnumerable<Product> beverages =
from p in NWEntities.Products
where p.Category.CategoryName == "Beverages"
orderby p.ProductName
select p;
Console.WriteLine("There are {0} Beverages",
beverages.Count());
// update one product
Product bev1 = beverages.ElementAtOrDefault(10);
if (bev1 != null)
{
decimal newPrice = (decimal)bev1.UnitPrice + 10.00m;
Console.WriteLine("The price of {0} is {1}. Update to {2}",
bev1.ProductName, bev1.UnitPrice, newPrice);
bev1.UnitPrice = newPrice;
}
// submit the change to database
NWEntities.SaveChanges();
// insert a product
Product newProduct = new Product
{
ProductName =
"new test product"
};
NWEntities.Products.Add(newProduct);
NWEntities.SaveChanges();
Console.WriteLine("Added a new product");
// delete a product
IQueryable<Product> productsToDelete =
from p in NWEntities.Products
where p.ProductName == "new test product"
select p;
if (productsToDelete.Count() > 0)
{
foreach (var p in productsToDelete)
{
NWEntities.Products.Remove(p);
Console.WriteLine("Deleted product {0}",
p.ProductID);
}
NWEntities.SaveChanges();
}
}
}
static void TestImplicitTransaction()
{
using (NorthwindEntities NWEntities = new NorthwindEntities())
{
Product prod1 = (from p in NWEntities.Products
where p.ProductID == 4
select p).First();
Product prod2 = (from p in NWEntities.Products
where p.ProductID == 5
select p).First();
prod1.UnitPrice += 1;
// update will be saved to database
NWEntities.SaveChanges();
Console.WriteLine("First update saved to database");
prod2.UnitPrice = -5;
// update will fail because UnitPrice can't be < 0
// but previous update stays in database
try
{
NWEntities.SaveChanges();
Console.WriteLine("Second update saved to database");
}
catch (Exception)
{
Console.WriteLine("Second update not saved to database");
}
}
}
static void TestExplicitTransaction()
{
using (NorthwindEntities NWEntities = new NorthwindEntities())
{
using (TransactionScope ts = new TransactionScope())
{
try
{
Product prod1 = (from p in NWEntities.Products
where p.ProductID == 4
select p).First();
prod1.UnitPrice += 1;
NWEntities.SaveChanges();
Console.WriteLine("First update saved to database, but not commited.");
// now let's try to update another product
Product prod2 = (from p in NWEntities.Products
where p.ProductID == 5
select p).First();
// update will fail because UnitPrice can't be < 0
prod2.UnitPrice = -5;
NWEntities.SaveChanges();
ts.Complete();
}
catch (Exception e)
{
// both updates will fail because they are within one transaction
Console.WriteLine("Exception caught. Rollback the first update.");
}
}
}
}
static void TestVersionControl()
{
using (NorthwindEntities NWEntities = new NorthwindEntities())
{
// first user
Console.WriteLine("First User ...");
Product product = (from p in NWEntities.Products
where p.ProductID == 3
select p).First();
Console.WriteLine("Original unit in stock: {0}",
product.UnitsInStock);
product.UnitsInStock += 1;
Console.WriteLine("Current unit in stock to update: {0}",
product.UnitsInStock);
// process more products
// second user
Console.WriteLine("\nSecond User ...");
using (NorthwindEntities1 NWEntities1 = new NorthwindEntities1())
{
Product1 product1 = (from p in NWEntities1.Product1s
where p.ProductID == 3
select p).First();
Console.WriteLine("Original unit in stock: {0}",
product1.UnitsInStock);
product1.UnitsInStock += 2;
Console.WriteLine("Current unit in stock to update: {0}",
product1.UnitsInStock);
NWEntities1.SaveChanges();
Console.WriteLine("update submitted to database");
}
// first user is ready to submit changes
Console.WriteLine("\nFirst User ...");
try
{
NWEntities.SaveChanges();
}
catch (DbUpdateConcurrencyException e)
{
Console.WriteLine("Conflicts detected. Refreshing ...");
var entry = e.Entries.Single();
entry.OriginalValues.SetValues(entry.GetDatabaseValues());
NWEntities.SaveChanges();
Console.WriteLine("update submitted to database after refresh");
}
}
}
