在ASP.NET Web API中使用OData

一.什么是OData
OData是一个开放的数据协议(Open Data Protocol)
在ASP.NET Web API中,
对于CRUD(create, read, update, and delete)应用比传统WebAPI增加了很大的灵活性
只要正确使用相关的协议，可以在同等情况下
对一个CRUD应用可以节约很多开发时间，从而提高开发效率

二.怎么搭建

做一个简单的订单查询示例
我们使用Code First模式创建两个实体对象Product(产品),Supplier(供应商)
1.新建一个ASP.NET Empty项目,选择上使用Web API,如下图

2.使用NuGet引用OData和EntityFramework程序集

3.在Models文件夹中增加Product(产品),Supplier(供应商)两个实体

public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
        public string Category { get; set; }
    [ForeignKey(</span><span style="color: #800000">"</span><span style="color: #800000">Supplier</span><span style="color: #800000">"</span><span style="color: #000000">)]
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">int</span>? SupplierId { <span style="color: #0000ff">get</span>; <span style="color: #0000ff">set</span><span style="color: #000000">; }
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">virtual</span> Supplier Supplier { <span style="color: #0000ff">get</span>; <span style="color: #0000ff">set</span><span style="color: #000000">; }
}

public class Supplier

{

public int Id { get; set; }

public string Name { get; set; }

public ICollection<Product> Products { get; set; }

}

4.增加ProductContext数据库上下文对象，并且在web.config中配置好ConnectionString

public class ProductContext : DbContext
    {
        public ProductContext()
            : base("Demo")
        { }
        public DbSet<Product> Products { get; set; }
        public DbSet<Supplier> Suppliers { get; set; }
    }

 

<connectionStrings>
        <add name="Demo" connectionString="Data Source=(localdb)\v11.0; 
        Initial Catalog=Demo; Integrated Security=True; MultipleActiveResultSets=True; 
        AttachDbFilename=|DataDirectory|Demo.mdf"
      providerName="System.Data.SqlClient" />
    </connectionStrings>

5.生成数据库
我们启动程序包管理控制台，运行如下3个命令，
把我们Code First生成的实体生成到数据库
PM> Enable-Migrations
PM> Add-Migration FirstInit
PM> Update-Database
然后我们可以在服务器资源管理器中看到我们生成的数据库表，如下图

6.接下来我们在WebApiConfig中注册我们的OData路由

using Demo2.Models;
using System.Web.OData.Builder;
using System.Web.OData.Extensions;
namespace Demo2
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            ODataModelBuilder builder = new ODataConventionModelBuilder();
            builder.EntitySet<Product>("Products");
            builder.EntitySet<Supplier>("Suppliers");
            config.MapODataServiceRoute("ODataRoute", null, builder.GetEdmModel());
        }
    }
}

7.接下来我们分别为Product和Supplier新建ODataController,


我们在上图中我们选择好模型类和数据上下文,
并重复上面两步为Supplier实体也生成对应的ODataController
注意：由于VS2013的OData模板中OData V3版本的模板，
引用的名称空间要从V3
using System.Web.Http;
using System.Web.Http.ModelBinding;
using System.Web.Http.OData;
using System.Web.Http.OData.Routing;
修改为V4
using System.Web.Http;
using System.Web.OData;

到此，我们的OData示例程序已经搭建完成，我们在浏览器里打开这个项目的时候
会出现如下

{
  "@odata.context":"http://localhost:8914/$metadata","value":[
    {
      "name":"Products","kind":"EntitySet","url":"Products"
    },{
      "name":"Suppliers","kind":"EntitySet","url":"Suppliers"
    }
  ]
}

表示已经搭建成功了

三.怎么使用
由于没有测试数据，我们开始先在数据库表里为Products和Suppliers增加一些测试数据


接下来我们看看一些简单的使用示例
在自动生成的ProductsController和SuppliersController中
已经为我们生成了如下一些Action

所以对于一些增加，修改，删除，更新我就不做过多示例，
这些都是和WebAPI没有什么太多区别，
我主要示例的是查询的使用，不得不说OData已经为我们把查询功能全做完了
示例1：列出所有Product
URL:http://localhost:8914/Products

{
  "@odata.context":"http://localhost:8914/$metadata#Products","value":[
    {
      "Id":1,"Name":"Products1","Price":100.00,"Category":"Test","SupplierId":1
    },{
      "Id":2,"Name":"Products2","Price":200.00,"Category":"Test","SupplierId":1
    },{
      "Id":3,"Name":"Products3","Price":300.00,"Category":"Test","SupplierId":1
    },{
      "Id":4,"Name":"Products4","Price":400.00,"Category":"P1","SupplierId":2
    },{
      "Id":5,"Name":"Products5","Price":500.00,"Category":"P1","SupplierId":2
    },{
      "Id":6,"Name":"Products6","Price":600.00,"Category":"P1","SupplierId":2
    },{
      "Id":7,"Name":"Products7","Price":700.00,"Category":"P1","SupplierId":2
    },{
      "Id":8,"Name":"Products8","Price":800.00,"Category":"Test","SupplierId":3
    },{
      "Id":9,"Name":"Products9","Price":900.00,"Category":"P1","SupplierId":3
    }
  ]
}

示例2,查询单个Products
URL:http://localhost:8914/Products(1) 其中(1)为Id

{
  "@odata.context":"http://localhost:8914/$metadata#Products/$entity","Id":1,"Name":"Products1","Price":100.00,"Category":"Test","SupplierId":1
}

示例3,查询Products,只列出Name,Price例
URL：http://localhost:8914/Products?$select=Name,Price

{
  "@odata.context":"http://localhost:8914/$metadata#Products(Name,Price)","value":[
    {
      "Name":"Products1","Price":100.00
    },{
      "Name":"Products2","Price":200.00
    },{
      "Name":"Products3","Price":300.00
    },{
      "Name":"Products4","Price":400.00
    },{
      "Name":"Products5","Price":500.00
    },{
      "Name":"Products6","Price":600.00
    },{
      "Name":"Products7","Price":700.00
    },{
      "Name":"Products8","Price":800.00
    },{
      "Name":"Products9","Price":900.00
    }
  ]
}

示例5：只列出ID为1的Products，只显示列Name,Price

URL:http://localhost:8914/Products(1)?$select=Name,Price

{
  "@odata.context":"http://localhost:8914/$metadata#Products(Name,Price)/$entity","Name":"Products1","Price":100.00
}

示例6：列出Products(只有列Name,Price),包括Supplier
URL:http://localhost:8914/Products?$select=Name,Price&$expand=Supplier

{
  "@odata.context":"http://localhost:8914/$metadata#Products(Name,Price,Supplier)","value":[
    {
      "Name":"Products1","Price":100.00,"Supplier":{
        "Id":1,"Name":"Supplier1"
      }
    },{
      "Name":"Products2","Price":200.00,"Supplier":{
        "Id":1,"Name":"Supplier1"
      }
    },{
      "Name":"Products3","Price":300.00,"Supplier":{
        "Id":1,"Name":"Supplier1"
      }
    },{
      "Name":"Products4","Price":400.00,"Supplier":{
        "Id":2,"Name":"Supplier2"
      }
    },{
      "Name":"Products5","Price":500.00,"Supplier":{
        "Id":2,"Name":"Supplier2"
      }
    },{
      "Name":"Products6","Price":600.00,"Supplier":{
        "Id":2,"Name":"Supplier2"
      }
    },{
      "Name":"Products7","Price":700.00,"Supplier":{
        "Id":2,"Name":"Supplier2"
      }
    },{
      "Name":"Products8","Price":800.00,"Supplier":{
        "Id":3,"Name":"Supplier3"
      }
    },{
      "Name":"Products9","Price":900.00,"Supplier":{
        "Id":3,"Name":"Supplier3"
      }
    }
  ]
}

示例7:过滤Products,只显示分类为Test的数据
URL:http://localhost:8914/Products?$filter=Category eq ’Test‘

{
  "@odata.context":"http://localhost:8914/$metadata#Products","value":[
    {
      "Id":1,"Name":"Products1","Price":100.00,"Category":"Test","SupplierId":1
    },{
      "Id":2,"Name":"Products2","Price":200.00,"Category":"Test","SupplierId":1
    },{
      "Id":3,"Name":"Products3","Price":300.00,"Category":"Test","SupplierId":1
    },{
      "Id":8,"Name":"Products8","Price":800.00,"Category":"Test","SupplierId":3
    }
  ]
}

示例8:过滤Products,只显示分类为Test的数据,并排序
URL：http://localhost:8914/Products?$filter=Category eq ’Test‘&$orderby=Price desc

{
  "@odata.context":"http://localhost:8914/$metadata#Products","value":[
    {
      "Id":8,"Name":"Products8","Price":800.00,"Category":"Test","SupplierId":3
    },{
      "Id":3,"Name":"Products3","Price":300.00,"Category":"Test","SupplierId":1
    },{
      "Id":2,"Name":"Products2","Price":200.00,"Category":"Test","SupplierId":1
    },{
      "Id":1,"Name":"Products1","Price":100.00,"Category":"Test","SupplierId":1
    }
  ]
}

下面是$filter的其它的使用方式
1.  http://localhost/Products?$filter=Category eq 'Test'
过滤Category=Test
2.http://localhost/Products?$filter=Price lt 10
过滤Price小于10
3。http://localhost/Products?$filter=Price ge 5 and Price le 15
过滤5<=Price>=15
5,还可以使用数据库函数如：
$filter=substringof('zz',Name)
$filter=year(ReleaseDate) gt 2005

关于排序
$orderby=Price
$orderby=Price desc
$orderby=Category,Price desc

还有一些过滤器如
$skip，$top,$inlinecount等等
所以OData基本上实现我们们想要查询的相关方法
对于CURD程序的查询来说大大提高开发效率

四: 相关引用资源
https://www.asp.net/web-api
https://www.asp.net/web-api/overview/odata-support-in-aspnet-web-api/odata-v4/create-an-odata-v4-endpoint

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