在ASP.NET Web API中使用OData

http://www.alixixi.com/program/a/2015063094986.shtml

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=DataDirectoryDemo.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