private static void SimpleLinq(EntitiesModel context)
{
Console.WriteLine("No Fetch optimization:");
var query1 = context.Cars.Where(c => c.CarYear < 2000).ToList();
Console.WriteLine("Car\tCategory");
foreach (var car in query1)
{
Console.WriteLine("{0}\t{1}", car.CarID, car.Category.CategoryName);
}
}
static void Main(string[] args)
{
using(var context = new EntitiesModel())
{
context.Log = Console.Out;
//SimpleLinq(context);
//LinqWithFetchStrategy(context);
//DynamicLinq(context);
//CommonLinqMistakes(context);
//BulkUpdate(context);
//BulkDelete(context);
}
}
private static void DynamicLinq(EntitiesModel context)
{
// strongly typed dynamic LINQ
Console.WriteLine("Dynamic strongly typed LINQ Where:");
var query1 = context.Cars.Where("CarYear < @0", 2000).ToList();
Console.WriteLine("Car\tCategory");
foreach (var car in query1)
{
Console.WriteLine("{0}\t{1}", car.CarID, car.Category.CategoryName);
}
// weakly typed dynamic LINQ with projection
Console.WriteLine("Dynamic weakly typed LINQ Where and Select:");
var objList = context.GetAll("OpenAccessModel9.Car").Where("CarYear < @0", 2000)
.Select("new (CarID as Id, CarYear)")
.Cast<object>().ToList();
foreach (object objCar in objList)
{
Console.WriteLine(objCar);
}
}
private static void LinqWithFetchStrategy(EntitiesModel context)
{
Console.WriteLine("With fetch optimization:");
FetchStrategy strategy = new FetchStrategy();
strategy.LoadWith<Car>(c => c.Category);
strategy.LoadWith<Category>(cat => cat.RentalRates);
// set the strategy to the context
context.FetchStrategy = strategy;
var query2 = context.Cars//.Include(c => c.Category)
//.Include(c => c.Category.RentalRates.Select(r=>r.SubRates))
.Where(c => c.CarYear < 2000).ToList();
Console.WriteLine("Car\tCategory");
foreach (var car in query2)
{
Console.WriteLine("{0}\t{1}", car.CarID, car.Category.CategoryName);
}
// remove the strategy
context.FetchStrategy = null;
}
private static void CommonLinqMistakes(EntitiesModel context)
{
Console.WriteLine("Common mistakes:");
Console.WriteLine("Calling .ToList too early:");
var query1 = context.Cars.ToList().Where(c => c.Make == "VW");
Console.WriteLine("************");
Console.WriteLine("Calling CLR method in Where:");
var query2 = context.Cars.Where(c => SomeMethod(c) == "42");
string query2Text = query2.ToString();
var query2Result = query2.ToList();
Console.WriteLine("************");
Console.WriteLine("Using projection will not fill the L1 and L2 caches");
var query3 = context.Cars.Select(c => new { Id = c.CarID, Name = c.Make + c.Model });
var query3Text = query3.ToString();
Console.WriteLine("************");
Console.WriteLine("Getting too much data:");
var query4 = context.Cars.Where(c => c.Make == "BMW");
var query4Text = query4.ToString();
var query4Result = query4.ToList().Count(); // we don't need the whole list of fully loaded cars to count them!
Console.WriteLine("************");
Console.WriteLine("Using constants and other non-cacheable pieces instead of parameters:");
string make = "BMW";
Console.WriteLine("With parameter:");
var query5 = context.Cars.Where(c => c.Make == make); // make is converted into parameter and the query is cached properly
var query5Text = query5.ToString();
Console.WriteLine("Without parameter:");
var query6 = context.Cars.Where(c => c.Make == "BMW"); // "BMW" cannot be converted to parameter and the query will not be reused if "BMW' is changed to "VW"
var query6Text = query6.ToString();
Console.WriteLine("************");
Console.WriteLine("Disposing context before enumerating the query result");
IQueryable<Car> query7 = null;
using (EntitiesModel ctx = new EntitiesModel())
{
query7 = ctx.Cars.Where(c => c.Make == "BMW");
}
Console.WriteLine("Car\tCategory");
foreach (var car in query7)
{
Console.WriteLine("{0}\t{1}", car.CarID, car.Category.CategoryName);
}
Console.WriteLine("************");
}
private static void BulkDelete(EntitiesModel context)
{
// avoid showing the INSERT statements that populate the data
context.Log = null;
for (int i = 0; i < 10; i++)
{
Car car = new Car() { Make = "BMW", Model = "1020", CarYear = 2018, Available = true, CategoryID = 1, TagNumber = i.ToString()};
context.Add(car);
}
context.SaveChanges();
// show the delete statements
context.Log = Console.Out;
var query = context.GetAll<Car>().Where(c => c.CarYear > DateTime.Now.Year);
int deleted = query.DeleteAll();
Console.WriteLine("Deleted cars: {0}", deleted);
}
private static void BulkUpdate(EntitiesModel context)
{
string tooOldName = "Too old";
Category tooOldCategory = context.Categories.FirstOrDefault(c => c.CategoryName == tooOldName);
if (tooOldCategory == null)
{
tooOldCategory = new Category();
tooOldCategory.CategoryName = tooOldName;
context.Add(tooOldCategory);
context.SaveChanges();
}
var query = context.GetAll<Car>().Where(c => c.CarYear < 2000);
int updated = query.UpdateAll(u => u.Set(c => c.Category, c => tooOldCategory)
.Set(c => c.Available, c => false));
Console.WriteLine("Updated cars: {0}", updated);
}
