Tutorial: Use async and stored procedures with EF in an ASP.NET MVC App
In earlier tutorials you learned how to read and update data using the synchronous programming model. In this tutorial you see how to implement the asynchronous programming model. Asynchronous code can help an application perform better because it makes better use of server resources.
In this tutorial you also see how to use stored procedures for insert, update, and delete operations on an entity.
Finally, you redeploy the application to Azure, along with all of the database changes that you've implemented since the first time you deployed.
The following illustrations show some of the pages that you'll work with.
In this tutorial, you:
- Learn about asynchronous code
- Create a Department controller
- Use stored procedures
- Deploy to Azure
Prerequisites
Why use asynchronous code
A web server has a limited number of threads available, and in high load situations all of the available threads might be in use. When that happens, the server can't process new requests until the threads are freed up. With synchronous code, many threads may be tied up while they aren't actually doing any work because they're waiting for I/O to complete. With asynchronous code, when a process is waiting for I/O to complete, its thread is freed up for the server to use for processing other requests. As a result, asynchronous code enables server resources to be use more efficiently, and the server is enabled to handle more traffic without delays.
In earlier versions of .NET, writing and testing asynchronous code was complex, error prone, and hard to debug. In .NET 4.5, writing, testing, and debugging asynchronous code is so much easier that you should generally write asynchronous code unless you have a reason not to. Asynchronous code does introduce a small amount of overhead, but for low traffic situations the performance hit is negligible, while for high traffic situations, the potential performance improvement is substantial.
For more information about asynchronous programming, see Use .NET 4.5's async support to avoid blocking calls.
Create Department controller
Create a Department controller the same way you did the earlier controllers, except this time select the Use async controller actions check box.
The following highlights show what was added to the synchronous code for the Index
method to make it asynchronous:
public async Task<ActionResult> Index()
{
var departments = db.Departments.Include(d => d.Administrator);
return View(await departments.ToListAsync());
}
Four changes were applied to enable the Entity Framework database query to execute asynchronously:
- The method is marked with the
async
keyword, which tells the compiler to generate callbacks for parts of the method body and to automatically create theTask<ActionResult>
object that is returned. - The return type was changed from
ActionResult
toTask<ActionResult>
. TheTask<T>
type represents ongoing work with a result of typeT
. - The
await
keyword was applied to the web service call. When the compiler sees this keyword, behind the scenes it splits the method into two parts. The first part ends with the operation that is started asynchronously. The second part is put into a callback method that is called when the operation completes. - The asynchronous version of the
ToList
extension method was called.
Why is the departments.ToList
statement modified but not the departments = db.Departments
statement? The reason is that only statements that cause queries or commands to be sent to the database are executed asynchronously. The departments = db.Departments
statement sets up a query but the query is not executed until the ToList
method is called. Therefore, only the ToList
method is executed asynchronously.
In the Details
method and the HttpGet
Edit
and Delete
methods, the Find
method is the one that causes a query to be sent to the database, so that's the method that gets executed asynchronously:
public async Task<ActionResult> Details(int? id)
{
if (id == null)
{
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
}
Department department = await db.Departments.FindAsync(id);
if (department == null)
{
return HttpNotFound();
}
return View(department);
}
In the Create
, HttpPost Edit
, and DeleteConfirmed
methods, it is the SaveChanges
method call that causes a command to be executed, not statements such as db.Departments.Add(department)
which only cause entities in memory to be modified.
public async Task<ActionResult> Create(Department department)
{
if (ModelState.IsValid)
{
db.Departments.Add(department);
await db.SaveChangesAsync();
return RedirectToAction("Index");
}
Open Views\Department\Index.cshtml, and replace the template code with the following code:
@model IEnumerable<ContosoUniversity.Models.Department>
@{
ViewBag.Title = "Departments";
}
<h2>Departments</h2>
<p>
@Html.ActionLink("Create New", "Create")
</p>
<table class="table">
<tr>
<th>
@Html.DisplayNameFor(model => model.Name)
</th>
<th>
@Html.DisplayNameFor(model => model.Budget)
</th>
<th>
@Html.DisplayNameFor(model => model.StartDate)
</th>
<th>
Administrator
</th>
<th></th>
</tr>
@foreach (var item in Model) {
<tr>
<td>
@Html.DisplayFor(modelItem => item.Name)
</td>
<td>
@Html.DisplayFor(modelItem => item.Budget)
</td>
<td>
@Html.DisplayFor(modelItem => item.StartDate)
</td>
<td>
@Html.DisplayFor(modelItem => item.Administrator.FullName)
</td>
<td>
@Html.ActionLink("Edit", "Edit", new { id=item.DepartmentID }) |
@Html.ActionLink("Details", "Details", new { id=item.DepartmentID }) |
@Html.ActionLink("Delete", "Delete", new { id=item.DepartmentID })
</td>
</tr>
}
</table>
This code changes the title from Index to Departments, moves the Administrator name to the right, and provides the full name of the administrator.
In the Create, Delete, Details, and Edit views, change the caption for the InstructorID
field to "Administrator" the same way you changed the department name field to "Department" in the Course views.
In the Create and Edit views use the following code:
<label class="control-label col-md-2" for="InstructorID">Administrator</label>
In the Delete and Details views use the following code:
<dt>
Administrator
</dt>
Run the application, and click the Departments tab.
Everything works the same as in the other controllers, but in this controller all of the SQL queries are executing asynchronously.
Some things to be aware of when you are using asynchronous programming with the Entity Framework:
- The async code is not thread safe. In other words, don't try to do multiple operations in parallel using the same context instance.
- If you want to take advantage of the performance benefits of async code, make sure that any library packages that you're using (such as for paging), also use async if they call any Entity Framework methods that cause queries to be sent to the database.
Use stored procedures
Some developers and DBAs prefer to use stored procedures for database access. In earlier versions of Entity Framework you can retrieve data using a stored procedure by executing a raw SQL query, but you can't instruct EF to use stored procedures for update operations. In EF 6 it's easy to configure Code First to use stored procedures.
In DAL\SchoolContext.cs, add the highlighted code to the
OnModelCreating
method.protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); modelBuilder.Entity<Course>() .HasMany(c => c.Instructors).WithMany(i => i.Courses) .Map(t => t.MapLeftKey("CourseID") .MapRightKey("InstructorID") .ToTable("CourseInstructor")); modelBuilder.Entity<Department>().MapToStoredProcedures(); }
This code instructs Entity Framework to use stored procedures for insert, update, and delete operations on the
Department
entity.In Package Manage Console, enter the following command:
add-migration DepartmentSP
Open Migrations\<timestamp>_DepartmentSP.cs to see the code in the
Up
method that creates Insert, Update, and Delete stored procedures:public override void Up() { CreateStoredProcedure( "dbo.Department_Insert", p => new { Name = p.String(maxLength: 50), Budget = p.Decimal(precision: 19, scale: 4, storeType: "money"), StartDate = p.DateTime(), InstructorID = p.Int(), }, body: @"INSERT [dbo].[Department]([Name], [Budget], [StartDate], [InstructorID]) VALUES (@Name, @Budget, @StartDate, @InstructorID) DECLARE @DepartmentID int SELECT @DepartmentID = [DepartmentID] FROM [dbo].[Department] WHERE @@ROWCOUNT > 0 AND [DepartmentID] = scope_identity() SELECT t0.[DepartmentID] FROM [dbo].[Department] AS t0 WHERE @@ROWCOUNT > 0 AND t0.[DepartmentID] = @DepartmentID" ); CreateStoredProcedure( "dbo.Department_Update", p => new { DepartmentID = p.Int(), Name = p.String(maxLength: 50), Budget = p.Decimal(precision: 19, scale: 4, storeType: "money"), StartDate = p.DateTime(), InstructorID = p.Int(), }, body: @"UPDATE [dbo].[Department] SET [Name] = @Name, [Budget] = @Budget, [StartDate] = @StartDate, [InstructorID] = @InstructorID WHERE ([DepartmentID] = @DepartmentID)" ); CreateStoredProcedure( "dbo.Department_Delete", p => new { DepartmentID = p.Int(), }, body: @"DELETE [dbo].[Department] WHERE ([DepartmentID] = @DepartmentID)" ); }
In Package Manage Console, enter the following command:
update-database
Run the application in debug mode, click the Departments tab, and then click Create New.
Enter data for a new department, and then click Create.
In Visual Studio, look at the logs in the Output window to see that a stored procedure was used to insert the new Department row.
Code First creates default stored procedure names. If you are using an existing database, you might need to customize the stored procedure names in order to use stored procedures already defined in the database. For information about how to do that, see Entity Framework Code First Insert/Update/Delete Stored Procedures.
If you want to customize what generated stored procedures do, you can edit the scaffolded code for the migrations Up
method that creates the stored procedure. That way your changes are reflected whenever that migration is run and will be applied to your production database when migrations runs automatically in production after deployment.
If you want to change an existing stored procedure that was created in a previous migration, you can use the Add-Migration command to generate a blank migration, and then manually write code that calls the AlterStoredProcedure method.
Deploy to Azure
This section requires you to have completed the optional Deploying the app to Azure section in the Migrations and Deployment tutorial of this series. If you had migrations errors that you resolved by deleting the database in your local project, skip this section.
In Visual Studio, right-click the project in Solution Explorer and select Publish from the context menu.
Click Publish.
Visual Studio deploys the application to Azure, and the application opens in your default browser, running in Azure.
Test the application to verify it's working.
The first time you run a page that accesses the database, the Entity Framework runs all of the migrations
Up
methods required to bring the database up to date with the current data model. You can now use all of the web pages that you added since the last time you deployed, including the Department pages that you added in this tutorial.
Get the code
Download the Completed Project
Additional resources
Links to other Entity Framework resources can be found in the ASP.NET Data Access - Recommended Resources.
Next steps
In this tutorial, you:
- Learned about asynchronous code
- Created a Department controller
- Used stored procedures
- Deployed to Azure
Advance to the next article to learn how to handle conflicts when multiple users update the same entity at the same time.