ASP.NET Web API教程 建立Admin控制器執行個體分享

In this section, we'll add a Web API controller that supports CRUD (create, read, update, and delete) operations on products. The controller will use Entity Framework to communicate with the database layer. Only administrators will be able to use this controller. Customers will access the products through another controller.
在本小節中，我們要添加一個對產品支援CRUD（建立、讀取、更新和刪除）操作的Web API控制器。該控制器將使用Entity Framework與資料庫層進行通訊。只有管理員才能夠使用這個控制器。用戶端將通過另一個控制器訪問產品。
In Solution Explorer, right-click the Controllers folder. Select Add and then Controller.
在“方案總管”中右擊Controllers檔案夾，選擇“添加”，然後選“控制器”（見圖2-16）。

圖2-16. 添加控制器
In the Add Controller dialog, name the controller AdminController. Under Template, select "API controller with read/write actions, using Entity Framework". Under Model class, select "Product (ProductStore.Models)". Under Data Context, select "<New Data Context>".
在“添加控制器”對話方塊中，將此控制器命名為AdminController。在“模板”下選擇“帶有讀/寫動作的API控制器（用Entity Framework）”。在“模型類”下選擇“Product (ProductStore.Models)”。在“資料內容”下選擇“<新資料內容>”（見圖2-17）。

圖2-17. 添加控制器對話方塊中的設定
If the Model class drop-down does not show any model classes, make sure you compiled the project. Entity Framework uses reflection, so it needs the compiled assembly.
如果“模型類”下拉式清單未顯示任何模型類，請確保已編譯了此項目。Entity Framework使用反射，因此它需要已編譯的程式集。
Selecting "<New Data Context>" will open the New Data Context dialog. Name the data context ProductStore.Models.OrdersContext.
選擇“<新資料內容>”會開啟“新資料內容”對話方塊。將該資料內容命名為ProductStore.Models.OrdersContext（見圖2-18）。

圖2-18. 命名“新資料內容”
Click OK to dismiss the New Data Context dialog. In the Add Controller dialog, click Add.
點擊“OK”退出這個“新資料內容”對話方塊。在“添加控制器”對話方塊中點擊“添加”。
Here's what got added to the project:
以下是添加到項目的內容：
A class named OrdersContext that derives from DbContext. This class provides the glue between the POCO models and the database.
一個名稱為的OrdersContext類，它派生於DbContext。這個類提供了POCO模型與資料庫之間的粘合。
A Web API controller named AdminController. This controller supports CRUD operations on Product instances. It uses the OrdersContext class to communicate with Entity Framework.
一個名稱為AdminController的Web API控制器。這個控制器支援對Product執行個體的CRUD操作。它使用OrdersContext類與Entity Framework進行通訊。
A new database connection string in the Web.config file.
Web.config檔案中的一個新的資料庫連接字串。
上述新添加項見圖2-19。

圖2-19. 新添加到項目的內容
Open the OrdersContext.cs file. Notice that the constructor specifies the name of the database connection string. This name refers to the connection string that was added to Web.config.
開啟OrdersContext.cs檔案。注意，其構造器指明了資料庫連接字串的名稱。該名稱是指被添加到Web.config的連接字串。 複製代碼 代碼如下:public OrdersContext() : base("name=OrdersContext")Add the following properties to the OrdersContext class:

將以下屬性添加到OrdersContext類： 複製代碼 代碼如下:public DbSet<Order> Orders { get; set; }
public DbSet<OrderDetail> OrderDetails { get; set; }

A DbSet represents a set of entities that can be queried. Here is the complete listing for the OrdersContext class:
DbSet表示一組能夠被查詢的實體。以下是這個OrdersContext類的完整清單： 複製代碼 代碼如下:public class OrdersContext : DbContext
{
public OrdersContext() : base("name=OrdersContext")
{
}
public DbSet<Order> Orders { get; set; }
public DbSet<OrderDetail> OrderDetails { get; set; }
public DbSet<Product> Products { get; set; }
}

The AdminController class defines five methods that implement basic CRUD functionality. Each method corresponds to a URI that the client can invoke:
類定義了實現基本的CRUD功能的五個方法。每個方法對應於一個用戶端可以請求的URI（見表2-2）：
表2-2. AdminController中實現CRUD操作的五個方法
table
Each method calls into OrdersContext to query the database. The methods that modify the collection (PUT, POST, and DELETE) call db.SaveChanges to persist the changes to the database. Controllers are created per HTTP request and then disposed, so it is necessary to persist changes before a method returns.
每一個方法調用都會進入OrdersContext對資料庫進行查詢。對資料集進行修改的方法（PUT、POST以及DELETE）會調用db.SaveChanges，以便把這些修改持久化回資料庫。每個HTTP請求都會建立控制器（執行個體），然後清除它。因此，在一個方法返回之前，對修改持久化是必要的。
Add a Database Initializer
添加資料庫初始化器
Entity Framework has a nice feature that lets you populate the database on startup, and automatically recreate the database whenever the models change. This feature is useful during development, because you always have some test data, even if you change the models.
Entity Framework有一個很好的特性，它讓你在（應用程式）啟動時填充資料庫，並在模型發生修改時重建資料庫。這個特性在開發期間是有用的，因為你總會有一些測試資料，甚至會修改模型。
In Solution Explorer, right-click the Models folder and create a new class named OrdersContextInitializer. Paste in the following implementation:
在“方案總管”中，右擊Models檔案夾，並建立一個名稱為OrdersContextInitializer的新類。粘貼以下實現： 複製代碼 代碼如下:namespace ProductStore.Models
{
using System;
using System.Collections.Generic;
using System.Data.Entity;
public class OrdersContextInitializer : DropCreateDatabaseIfModelChanges<OrdersContext>
{
protected override void Seed(OrdersContext context)
{
var products = new List<Product>()
{
new Product() { Name = "Tomato Soup", Price = 1.39M, ActualCost = .99M },
new Product() { Name = "Hammer", Price = 16.99M, ActualCost = 10 },
new Product() { Name = "Yo yo", Price = 6.99M, ActualCost = 2.05M }
};
products.ForEach(p => context.Products.Add(p));
context.SaveChanges();
var order = new Order() { Customer = "Bob" };
var od = new List<OrderDetail>()
{
new OrderDetail() { Product = products[0], Quantity = 2, Order = order},
new OrderDetail() { Product = products[1], Quantity = 4, Order = order }
};
context.Orders.Add(order);
od.ForEach(o => context.OrderDetails.Add(o));
context.SaveChanges();
}
}
}

By inheriting from the DropCreateDatabaseIfModelChanges class, we are telling Entity Framework to drop the database whenever we modify the model classes. When Entity Framework creates (or recreates) the database, it calls the Seed method to populate the tables. We use the Seed method to add some example products plus an example order.
通過對DropCreateDatabaseIfModelChanges類的繼承，我們是在告訴Entity Framework，無論何時修改了模型類，便刪除資料庫。當Entity Framework建立（或重建）資料庫時，它會調用Seed方法去填充資料庫。我們用這個Seed方法添加了一些例子產品和一個例子訂單。
This feature is great for testing, but don't use the DropCreateDatabaseIfModelChanges class in production, because you could lose your data if someone changes a model class.
這個特性對於測試是很棒的，但在產品（指正式啟動並執行應用程式 — 譯者注）中不要使用這個DropCreateDatabaseIfModelChanges類。因為，如果有人修改了模型類，便會遺失資料。
Next, open Global.asax and add the following code to the Application_Start method:
下一步，開啟Global.asax，並將以下代碼添加到Application_Start方法中： 複製代碼 代碼如下:System.Data.Entity.Database.SetInitializer(
new ProductStore.Models.OrdersContextInitializer());Send a Request to the Controller

向控制器發送請求
At this point, we haven't written any client code, but you can invoke the web API using a web browser or an HTTP debugging tool such as Fiddler. In Visual Studio, press F5 to start debugging. Your web browser will open to http://localhost:portnum/, where portnum is some port number.
此刻，我們還沒有編寫任何用戶端代碼，但你已經可以使用Web瀏覽器或諸如Fiddler之類的調試工具來調用這個Web API了。在Visual Studio中按F5鍵啟動調試。你的瀏覽器將開啟網址http://localhost:portnum/，這裡，portnum是某個連接埠號碼。
Send an HTTP request to "http://localhost:portnum/api/admin". The first request may be slow to complete, because Entify Entity Framework needs to create and seed the database. The response should something similar to the following:
發送一個HTTP請求到“http://localhost:portnum/api/admin”。第一次請求可能會慢一些才能完成，因為Entity Framework需要建立和種植資料庫。其響應應當類似於下面這樣： 複製代碼 代碼如下:HTTP/1.1 200 OK
Server: ASP.NET Development Server/10.0.0.0
Date: Mon, 18 Jun 2012 04:30:33 GMT
X-AspNet-Version: 4.0.30319
Cache-Control: no-cache
Pragma: no-cache
Expires: -1
Content-Type: application/json; charset=utf-8
Content-Length: 175
Connection: Close
[{"Id":1,"Name":"Tomato Soup","Price":1.39,"ActualCost":0.99},{"Id":2,"Name":"Hammer",
"Price":16.99,"ActualCost":10.00},{"Id":3,"Name":"Yo yo","Price":6.99,"ActualCost":
2.05}]

看完此文如果覺得有所收穫，懇請給個推薦