EF6 Onwards Only - The features, APIs, etc. discussed in this page were introduced in Entity Framework 6. If you are using an earlier version, some or all of the information does not apply.
EF6 introduced support for asynchronous query and save using the async and await keywords that were introduced in .NET 4.5. While not all applications may benefit from asynchrony, it can be used to improve client responsiveness and server scalability when handling long-running, network or IO-bound tasks.
The following topics are covered on this page:
The purpose of this walkthrough is to introduce the async concepts in a way that makes it easy to observe the difference between asynchronous and synchronous program execution. This walkthrough is not intended to illustrate any of the key scenarios where async programming provides benefits.
Async programming is primarily focused on freeing up the current managed thread (thread running .NET code) to do other work while it waits for an operation that does not require any compute time from a managed thread. For example, whilst the database engine is processing a query there is nothing to be done by .NET code.
In client applications (WinForms, WPF, etc.) the current thread can be used to keep the UI responsive while the async operation is performed. In server applications (ASP.NET etc.) the thread can be used to process other incoming requests - this can reduce memory usage and/or increase throughput of the server.
In most applications using async will have no noticeable benefits and even could be detrimental. Use tests, profiling and common sense to measure the impact of async in your particular scenario before committing to it.
Here are some more resources to learn about async:
We’ll be using the Code First workflow to create our model and generate the database, however the asynchronous functionality will work with all EF models including those created with the EF Designer.
using System.Collections.Generic;
using System.Data.Entity;
namespace AsyncDemo
{
public class BloggingContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
public DbSet<Post> Posts { get; set; }
}
public class Blog
{
public int BlogId { get; set; }
public string Name { get; set; }
public virtual List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogId { get; set; }
public virtual Blog Blog { get; set; }
}
}
Now that we have an EF model, let‘s write some code that uses it to perform some data access.
using System;
using System.Linq;
namespace AsyncDemo
{
class Program
{
static void Main(string[] args)
{
PerformDatabaseOperations();
Console.WriteLine();
Console.WriteLine("Quote of the day");
Console.WriteLine(" Don‘t worry about the world coming to an end today... ");
Console.WriteLine(" It‘s already tomorrow in Australia.");
Console.WriteLine();
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
public static void PerformDatabaseOperations()
{
using (var db = new BloggingContext())
{
// Create a new blog and save it
db.Blogs.Add(new Blog
{
Name = "Test Blog #" + (db.Blogs.Count() + 1)
});
db.SaveChanges();
// Query for all blogs ordered by name
var blogs = (from b in db.Blogs
orderby b.Name
select b).ToList();
// Write all blogs out to Console
Console.WriteLine();
Console.WriteLine("All blogs:");
foreach (var blog in blogs)
{
Console.WriteLine(" " + blog.Name);
}
}
}
}
}This code calls the PerformDatabaseOperations method which saves a new Blog to the database and then retrieves all Blogs from the database and prints them to the Console. After this, the program writes a quote of the day to the Console.
Since the code is syncronous, we can observe the following execution flow when we run the program:
.png)
Now that we have our program up and running, we can begin making use of the new async and await keywords. We‘ve made the following changes to Program.cs
For a comprehensive list of available extension methods in the System.Data.Entity namespace, refer to the QueryableExtensions class. You’ll also need to add “using System.Data.Entity” to your using statements.
using System;
using System.Data.Entity;
using System.Linq;
using System.Threading.Tasks;
namespace AsyncDemo
{
class Program
{
static void Main(string[] args)
{
var task = PerformDatabaseOperations();
Console.WriteLine("Quote of the day");
Console.WriteLine(" Don‘t worry about the world coming to an end today... ");
Console.WriteLine(" It‘s already tomorrow in Australia.");
task.Wait();
Console.WriteLine();
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
public static async Task PerformDatabaseOperations()
{
using (var db = new BloggingContext())
{
// Create a new blog and save it
db.Blogs.Add(new Blog
{
Name = "Test Blog #" + (db.Blogs.Count() + 1)
});
Console.WriteLine("Calling SaveChanges.");
await db.SaveChangesAsync();
Console.WriteLine("SaveChanges completed.");
// Query for all blogs ordered by name
Console.WriteLine("Executing query.");
var blogs = await (from b in db.Blogs
orderby b.Name
select b).ToListAsync();
// Write all blogs out to Console
Console.WriteLine("Query completed with following results:");
foreach (var blog in blogs)
{
Console.WriteLine(" - " + blog.Name);
}
}
}
}
}Now that the code is asyncronous, we can observe a different execution flow when we run the program:
.png)
We now saw how easy it is to make use of EF’s asynchronous methods. Although the advantages of async may not be very apparent with a simple console app, these same strategies can be applied in situations where long-running or network-bound activities might otherwise block the application, or cause a large number of threads to increase the memory footprint.
Async Query & Save (EF6 onwards)
原文：http://www.cnblogs.com/pengyou8696/p/3550091.html