【ASP.NET Web API教程】2.1 创建支持CRUD操作的Web API

2.1 Creating a Web API that Supports CRUD Operations
2.1 创建支持CRUD操作的Web API

By Mike Wasson | January 28, 2012
作者:Mike Wasson | 日期:2012-1-28


注:本文是ASP.NET Web API系列教程第2章中的第1篇,因此标题采用了“2.1” — 译者注

This tutorial shows how to support CRUD operations in an HTTP service using ASP.NET Web API.
本教程展示如果在使用ASP.NET Web API的HTTP服务中支持CRUD操作。

CRUD stands for "Create, Read, Update, and Delete," which are the four basic database operations. Many HTTP services also model CRUD operations through REST or REST-like APIs.

In this tutorial, you will build a very simple web API to manage a list of products. Each product will contain a name, price, and category (such as "toys" or "hardware"), plus a product ID.
在本教程中,你将建立一个十分简单的Web API来管理一列产品。每个产品包含一个name(名称)、price(价格)和category(分类)(如,“toys(玩具)”、“hardware(硬件)”等),还有一个产品的ID。

The products API will expose following methods.

表2-1. Products API暴露的HTTP方法
HTTP method
Relative URI
Get a list of all products
GET /api/products
Get a product by ID
GET /api/products/id
Get a product by category
GET /api/products?category=category
Create a new product
POST /api/products
Update a product
PUT /api/products/id
Delete a product
DELETE /api/products/id

Notice that some of the URIs include the product ID in path. For example, to get the product whose ID is 28, the client sends a GET request for http://hostname/api/products/28.


The products API defines URIs for two resource types:

表2-2. 资源类型
The list of all the products.
An individual product.


The four main HTTP methods (GET, PUT, POST, and DELTETE) can be mapped to CRUD operations as follows:

  • GET retrieves the representation of the resource at a specified URI. GET should have no side effects on the server.
  • PUT updates a resource at a specified URI. PUT can also be used to create a new resource at a specified URI, if the server allows clients to specify new URIs. For this tutorial, the API will not support creation through PUT.
  • POST creates a new resource. The server assigns the URI for the new object and returns this URI as part of the response message.
  • DELETE deletes a resource at a specified URI.

Note: The PUT method replaces the entire product entity. That is, the client is expected to send a complete representation of the updated product. If you want to support partial updates, the PATCH method is preferred. This tutorial does not implement PATCH.

Create a New Web API Project
创建新的Web API项目

Start by running Visual Studio 2010 and select New Project from the Start page. Or, from the File menu, select New and then Project.
启动VS 2012,并在“开始页”选择“新项目”。或从“文件”菜单选择“新建”,然后选择“项目”。

In the Templates pane, select Installed Templates and expand the Visual C# node. Under Visual C#, select Web. In the list of project templates, select ASP.NET MVC 4 Web Application. Name the project "ProductStore" and click OK.
在“模板”面板中选择“已安装模板”,并展开“Visual C#”节点。选择该节点下的“Web”。在项目模板列表中选择“ASP.NET MVC 4 Web应用程序”。将此项目命名为“ProductStore”,点击“OK”(见图2-1)。


图2-1. 创建ProductStore项目

In the New ASP.NET MVC 4 Project dialog, select Web API and click OK.
在“新的ASP.NET MVC 4项目”对话框中选择“Web API”,点击“OK”(如图2-2)。


图2-2. 选择Web API模板

Adding a Model

A model is an object that represents the data in your application. In ASP.NET Web API, you can use strongly typed CLR objects as models, and they will automatically be serialized to XML or JSON for the client.
模型是表示你应用程序中数据的一种对象。在ASP.NET Web API中,你可以使用强类型的CRL(公共语言运行时)对象作为模型,而它们将被自动化地序列化成用于客户端的XML或JSON。

For the ProductStore API, our data consists of products, so we'll create a new class named Product.
对于这个ProductStore API,其数据由产品组成,因此,我们将创建一个名为Product的新类。

If Solution Explorer is not already visible, click the View menu and select Solution Explorer. In Solution Explorer, right-click the Models folder. From the context meny(menu), select Add, then select Class. Name the class "Product".


图2-3. 创建Product类

Add the following properties to the Product class.

namespace ProductStore.Models
    public class Product
        public int Id { get; set; }
        public string Name { get; set; }
        public string Category { get; set; }
        public decimal Price { get; set; }

Adding a Repository

We need to store a collection of products. It’s a good idea to separate the collection from our service implementation. That way, we can change the backing store without rewriting the service class. This type of design is called the repository pattern. Start by defining a generic interface for the repository.

In Solution Explorer, right-click the Models folder. Select Add, then select New Item.


图2-4. 创建新项

In the Templates pane, select Installed Templates and expand the C# node. Under C#, select Code. In the list of code templates, select Interface. Name the interface "IProductRepository".


图2-5. 创建接口

Add the following implementation:

namespace ProductStore.Models
    public interface IProductRepository 
        IEnumerable<Product> GetAll(); 
        Product Get(int id); 
        Product Add(Product item); 
        void Remove(int id); 
        bool Update(Product item); 

Now add another class to the Models folder, named "ProductRepository." This class will implement the IProductRespository interface. Add the following implementation:

namespace ProductStore.Models 
    public class ProductRepository : IProductRepository 
        private List<Product> products = new List<Product>(); 
        private int _nextId = 1; 
        public ProductRepository() 
            Add(new Product { Name = "Tomato soup", Category = "Groceries", Price = 1.39M }); 
            Add(new Product { Name = "Yo-yo", Category = "Toys", Price = 3.75M }); 
            Add(new Product { Name = "Hammer", Category = "Hardware", Price = 16.99M }); 
        public IEnumerable<Product> GetAll() 
            return products; 
        public Product Get(int id) 
            return products.Find(p => p.Id == id); 
        public Product Add(Product item) 
            if (item == null) 
                throw new ArgumentNullException("item"); 
            item.Id = _nextId++; 
            return item; 
        public void Remove(int id) 
            products.RemoveAll(p => p.Id == id); 
        public bool Update(Product item) 
            if (item == null) 
                throw new ArgumentNullException("item"); 
            int index = products.FindIndex(p => p.Id == item.Id); 
            if (index == -1) 
                return false; 
            return true; 

The repository keeps the list in local memory. This is OK for a tutorial, but in a real application, you would store the data externally, either a database or in cloud storage. The repository pattern will make it easier to change the implementation later.

Adding a Web API Controller
添加Web API控制器

If you have worked with ASP.NET MVC, then you are already familiar with controllers. In ASP.NET Web API, a controller is a class that handles HTTP requests from the client. The New Project wizard created two controllers for you when it created the project. To see them, expand the Controllers folder in Solution Explorer.
如果你曾使用过ASP.NET MVC,对控制器是熟悉的。在ASP.NET Web API中,控制器是一种处理客户端HTTP请求的类。“新项目”向导在创建项目时,为你创建了两个控制器。要看到它们,可以在“解决方案资源管理器”中展开Controllers文件夹。

  • HomeController is a traditional ASP.NET MVC controller. It is responsible for serving HTML pages for the site, and is not directly related to our web API.
    HomeController一个传统的ASP.NET MVC控制器。它负责对网站的HTML页面进行服务,而与Web API无直接关系。
  • ValuesController is an example WebAPI controller.

Go ahead and delete ValuesController, by right-clicking the file in Solution Explorer and selecting Delete. Now add a new controller, as follows:

In Solution Explorer, right-click the the Controllers folder. Select Add and then select Controller.


图2-6. 添加控制器

In the Add Controller wizard, name the controller "ProductsController". In the Template drop-down list, select Empty API Controller. Then click Add.


图2-7. 创建API控制器

It is not necessary to put your contollers into a folder named Controllers. The folder name is not important; it is simply a convenient way to organize your source files.

The Add Controller wizard will create a file named ProductsController.cs in the Controllers folder. If this file is not open already, double-click the file to open it. Add the following using statement:

using ProductStore.Models;

Add a field that holds an IProductRepository instance.

public class ProductsController : ApiController
    static readonly IProductRepository repository = new ProductRepository();

Calling new ProductRepository() in the controller is not the best design, because it ties the controller to a particular implementation of IProductRepository. For a better approach, see Using the Web API Dependency Resolver.
在控制器中调用new ProductRepository()不是最好的设计,因为它把控制器绑定到了IProductRepository的一个特定实现上了。更好的办法参见“使用Web API依赖性解析器”。

Getting a Resource

The ProductStore API will expose several "read" operations as HTTP GET methods:
这个ProductStore API将把几个“读取”操作暴露成HTTP的GET方法(见表2-3):

表2-3. 几个读取产品的URI
HTTP method
Relative URI
Get a list of all products
GET /api/products
Get a product by ID
GET /api/products/id
Get a product by category
GET /api/products?category=category

Here is the method to get the list of all products:

public IEnumerable<Product> GetAllProducts()
    return repository.GetAll();

The method name starts with "Get", so by convention it maps to GET requests. Also, because the method has no parameters, it maps to a URI that does not contain an "id" segment in the path.

Here is the method to get a product by ID:

public Product GetProduct(int id) 
    Product item = repository.Get(id); 
    if (item == null) 
        throw new HttpResponseException(HttpStatusCode.NotFound);  
    return item; 

This method name also starts with "Get", but the method has a parameter named id. This parameter is mapped to the "id" segment of the URI path. The ASP.NET Web API framework automatically converts the ID to the correct data type (int) for the parameter.
这个方法名也以“Get”开头,但该方法有一个名为id的参数。该参数被映射成URI路径的“id”片段。ASP.NET Web API框架自动地把这个ID转换成用于参数的正确的数据类型(int)。

The GetProduct method throws an exception of type HttpResponseException if id is not valid. This exception will be translated by the framework into a 404 (Not Found) error.

Finally, here is the method to find products by category:

public IEnumerable<Product> GetProductsByCategory(string category)
    return repository.GetAll().Where(
        p => string.Equals(p.Category, category, StringComparison.OrdinalIgnoreCase));

If the request URI has a query string, Web API tries to match the query parameters to parameters on the controller method. Therefore, a URI of the form "api/products?category=category" will map to this method.
如果请求URI有一个查询字符串,Web API会试图把这些查询参数(查询字符串中的参数 — 译者注)匹配成该控制器方法的参数。因此,一个“api/products?category=category”形式的URI会映射给这个方法。

Creating a Resource

To create a new product, the client sends an HTTP POST request, with the new product in the body of the request message.

Here is a simple implementation of the method:

// Not the final implementation!
// 非最终实现!
public Product PostProduct(Product item)
    item = repository.Add(item);
    return item;

To handle POST requests, we define a method whose name starts with "Post...". The method takes a parameter of type Product. By default, parameters with complex types are deserialized from the request body. Therefore, we expect the client to send us a serialized representation of a product object, using either XML or JSON for the serialization.

This implementation will work, but it is missing a couple of things.

  • Response code: By default, the Web API framework sets the response status code to 200 (OK). But according to the HTTP/1.1 protocol, when a POST request results in the creation of a resource, the server should reply with status 201 (Created).
    响应码(Response code):默认地,Web API框架把响应状态码设置为200(OK)。但根据HTTP/1.1协议,在POST请求形成资源创建时,服务器应当用状态201(已创建)进行回答。
  • Location: When the server creates a resource, it should include the URI of the new resource in the Location header of the response.

ASP.NET Web API makes it easy to manipulate the HTTP response message. Here is the improved implementation:
ASP.NET Web API操纵HTTP响应消息是很容易的。以下是经改进的实现:

public HttpResponseMessage PostProduct(Product item) 
    item = repository.Add(item); 
    var response = Request.CreateResponse<Product>(HttpStatusCode.Created, item); 
    string uri = Url.Link("DefaultApi", new { id = item.Id }); 
    response.Headers.Location = new Uri(uri); 
    return response; 

Notice that the method return type is now HttpResponseMessage. By returning an HttpResponseMessage instead of a Product, we can control the details of the HTTP response message, including the status code and the Location header.

The CreateResponse method creates an HttpResponseMessage and automatically writes a serialized representation of the Product object into the body fo of the response message.

This example does not validate the Product. For information about model validation, see Model Validation in ASP.NET Web API.
此例不验证Product。关于模型验证的信息,参阅“ASP.NET Web API中的模型验证”。

Updating a Resource

Updating a product with PUT is straightforward:

public void PutProduct(int id, Product product) 
    product.Id = id; 
    if (!repository.Update(product)) 
        throw new HttpResponseException(HttpStatusCode.NotFound); 

The method name starts with "Put...", so Web API matches it to PUT requests. The method takes two parameters, the product ID and the updated product. The id parameter is taken from the URI path, and the product parameter is deserialized from the request body. By default, the ASP.NET Web API framework takes simple parameter types from the route and complex types from the request body.
方法名以“Put…”开头,因此,Web API把它与PUT请求进行匹配。此方法采用两个参数,产品ID和被更新产品。Id参数取自URI路径,而product参数通过请求解序列化。默认地,ASP.NET Web API框架通过路由获取简单参数,而通过请求体获取复合类型。

Deleting a Resource

To delete a resourse, define a "Delete..." method.

public HttpResponseMessage DeleteProduct(int id) 
    return new HttpResponseMessage(HttpStatusCode.NoContent); 

According to the HTTP specification, the DELETE method must be idempotent, meaning that several DELETE requests to the same URI must have the same effect as a single DELETE request. Therefore, the method should not return an error code if the product was already deleted.

If a DELETE request succeeds, it can return status 200 (OK) with an entity-body that describes the status, or status 202 (Accepted) if the deletion is still pending, or status 204 (No Content) with no entity body. In this example, the method returns status 204.
一个成功的DELETE请求,可以返回200(OK)状态,并带有一个描述该状态的条目体;也可以在删除未决的情况下返回202(Accepted)状态;或者返回无条目体的204(No Content)状态。在本例中,该方法返回204状态。


By Mike Wasson, Mike Wasson is a programmer-writer at Microsoft.
Mike Wasson著,Mike Wasson是微软的一位程序员著作人。

posted @ 2012-11-12 07:36 r01cn 阅读(...) 评论(...) 编辑 收藏