static void ObjectTracking()
{
using (var context = new MenusContext())
{
//可以修改context的ChangeTracker行为
context.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
//这里m1和m2是相同对象, 因为查询到第二个对象和第一个对象具有相同主键，只实例化了第一个对象
var m1 = (from m in context.Menus where m.Text.StartsWith("Con") select m).FirstOrDefault();
var m2 = (from m in context.Menus where m.Text.Contains("(") select m).FirstOrDefault();
//如果使用AsNoTracking方法的话，可以不跟踪在数据库中运行查询的对象
//var m1 = (from m in context.Menus.AsNoTracking() where m.Text.StartsWith("Con") select m).FirstOrDefault();
if (ReferenceEquals(m1, m2))
{
Console.WriteLine("the same object");
}
else
{
Console.WriteLine("not the same");
}
ShowState(context);
}
}
public static void ShowState(MenusContext context)
{
//使用ChangeTracker可以访问所有上下文相关的对象的状态
//ChangeTracker.Entries()返回变更跟踪器了解的所有对象,将所有对象包括状态写入console
foreach (EntityEntry entry in context.ChangeTracker.Entries())
{
Console.WriteLine($"type: {entry.Entity.GetType().Name}, state: {entry.State}," +
$" {entry.Entity}");
}
}
private static async Task CreateDatabase()
{
using (var context = new MenusContext())
{
bool created = await context.Database.EnsureCreatedAsync();
string creationInfo = created ? "created" : "existed";
Console.WriteLine($"database {creationInfo}");
}
}
private static async Task DeleteDatabase()
{
Console.Write("Delete the database? ");
string input = Console.ReadLine();
if (input.ToLower() == "y")
{
using (var context = new MenusContext())
{
await context.Database.EnsureDeletedAsync();
}
}
}
private static void AddRecords()
{
Console.WriteLine(nameof(AddRecords));
try
{
using (var context = new MenusContext())
{
var soupCard = new MenuCard();
Menu[] soups =
{
new Menu
{
Text = "Consommé Célestine (with shredded pancake)",
Price = 4.8m,
MenuCard = soupCard
},
new Menu
{
Text = "Baked Potato Soup",
Price = 4.8m,
MenuCard = soupCard
},
new Menu
{
Text = "Cheddar Broccoli Soup",
Price = 4.8m,
MenuCard = soupCard
},
};
soupCard.Title = "Soups";
//soups会插入到Menus表
soupCard.Menus.AddRange(soups);
//soupCard插入到MenuCards表
context.MenuCards.Add(soupCard);
ShowState(context);
int records = context.SaveChanges();
Console.WriteLine($"{records} added");
Console.WriteLine();
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.WriteLine();
}
static void UpdateUntracked(Menu m)
{
using (var context = new MenusContext())
{
ShowState(context);
//显示的关联对象到上下文
//EntityEntry<Menu> entry = context.Menus.Attach(m);
//设置对象状态是Modified
//entry.State = EntityState.Modified;
//使用Update方法可以完成关联到上下文并设置对象状态为Modified
context.Menus.Update(m);
ShowState(context);
context.SaveChanges();
}
}
private static void ChangeUntracked()
{
Menu GetMenu()
{
using (var context = new MenusContext())
{
var menu = context.Menus.Skip(2).FirstOrDefault();
return(menu);
}
}
var m = GetMenu();
m.Price += 0.7m;
UpdateUntracked(m);
}
private static void UpdateRecords()
{
Console.WriteLine(nameof(UpdateRecords));
using (var context = new MenusContext())
{
Menu menu = context.Menus
.Skip(1)
.FirstOrDefault();
ShowState(context); //Unchanged
menu.Price += 0.2m;
ShowState(context); //Modified
int records = context.SaveChanges();
Console.WriteLine($"{records} updated");
ShowState(context); //Unchanded
}
Console.WriteLine();
}
static void AddHundredRecords()
{
Console.WriteLine(nameof(AddHundredRecords));
using (var context = new MenusContext())
{
var card = context.MenuCards.FirstOrDefault();
if (card != null)
{
var menus = Enumerable.Range(1, 100).Select(x => new Menu
{
MenuCard = card,
Text = $"$menu {x}",
Price = 9.9m
});
//这是一个批处理，一次性插入100条数据
context.Menus.AddRange(menus);
Stopwatch stopwatch = Stopwatch.StartNew();
int record = context.SaveChanges();
stopwatch.Stop();
Console.WriteLine($"{record} records added after ${stopwatch.ElapsedMilliseconds} ms");
}
}
}
