ASP.NET Web API中使用OData

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("Supplier")]
        public int? SupplierId { get; set; }
        public virtual Supplier Supplier { get; set; }
    }
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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