在ASP.NET Web API中使用OData

一.什麼是OData
OData是一個開放的數據協議(Open Data Protocol)
在ASP.NET Web API中,
對於CRUD(create, read, update, and delete)應用比傳統WebAPI增長了很大的靈活性
只要正確使用相關的協議，能夠在同等狀況下
對一個CRUD應用能夠節約不少開發時間，從而提升開發效率

二.怎麼搭建

作一個簡單的訂單查詢示例
咱們使用Code First模式建立兩個實體對象Product(產品),Supplier(供應商)
1.新建一個ASP.NET Empty項目,選擇上使用Web API,以下圖

2.使用NuGet引用OData和EntityFramework程序集

3.在Models文件夾中增長Product(產品),Supplier(供應商)兩個實體

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.增長ProductContext數據庫上下文對象，而且在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.生成數據庫
咱們啓動程序包管理控制檯，運行以下3個命令，
把咱們Code First生成的實體生成到數據庫
PM> Enable-Migrations
PM> Add-Migration FirstInit
PM> Update-Database
而後咱們能夠在服務器資源管理器中看到咱們生成的數據庫表，以下圖

6.接下來咱們在WebApiConfig中註冊咱們的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.接下來咱們分別爲Product和Supplier新建ODataController,


咱們在上圖中咱們選擇好模型類和數據上下文,
並重覆上面兩步爲Supplier實體也生成對應的ODataController
注意：因爲VS2013的OData模板中OData V3版本的模板，
引用的名稱空間要從V3
using System.Web.Http;
using System.Web.Http.ModelBinding;
using System.Web.Http.OData;
using System.Web.Http.OData.Routing;
修改成V4
using System.Web.Http;
using System.Web.OData;

到此，咱們的OData示例程序已經搭建完成，咱們在瀏覽器裏打開這個項目的時候
會出現以下

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

表示已經搭建成功了

三.怎麼使用
因爲沒有測試數據，咱們開始先在數據庫表裏爲Products和Suppliers增長一些測試數據


接下來咱們看看一些簡單的使用示例
在自動生成的ProductsController和SuppliersController中
已經爲咱們生成了以下一些Action

因此對於一些增長，修改，刪除，更新我就不作過多示例，
這些都是和WebAPI沒有什麼太多區別，
我主要示例的是查詢的使用，不得不說OData已經爲咱們把查詢功能全作完了
示例1：列出全部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,查詢單個Products
URL:http://localhost:8914/Products(1) 其中(1)爲Id

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

示例3,查詢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爲1的Products，只顯示列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:過濾Products,只顯示分類爲Test的數據
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:過濾Products,只顯示分類爲Test的數據,並排序
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'
過濾Category=Test
2.http://localhost/Products?$filter=Price lt 10
過濾Price小於10
3。http://localhost/Products?$filter=Price ge 5 and Price le 15
過濾5<=Price>=15
5,還能夠使用數據庫函數如：
$filter=substringof('zz',Name)
$filter=year(ReleaseDate) gt 2005

關於排序
$orderby=Price
$orderby=Price desc
$orderby=Category,Price desc

還有一些過濾器如
$skip，$top,$inlinecount等等
因此OData基本上實現咱們們想要查詢的相關方法
對於CURD程序的查詢來講大大提升開發效率

四: 相關引用資源
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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