一、OData介紹

開放數據協議（Open Data Protocol，縮寫OData）是一種描述如何創建和訪問Restful服務的OASIS標準。

二、OData 在asp.net mvc中的用法

　　1、在vs中新建webApi項目

2、添加測試類型

 public class Product
    {
        public int Id { get; set; }

        public string ProductName
        {
            get; set;
        }
    }

3、開啟EF自動遷移，添加EF上下文，

namespace ODataTest.Migrations
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Migrations;
    using System.Linq;
    using ODataTest.Models;

    internal sealed class Configuration : DbMigrationsConfiguration<ODataTest.Models.EFContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = true;
        }

        protected override void Seed(ODataTest.Models.EFContext context)
        {
            //  This method will be called after migrating to the latest version.

            //  You can use the DbSet<T>.AddOrUpdate() helper extension method 
            //  to avoid creating duplicate seed data.

        }
    }
}

 public class EFContext : DbContext
    {

        static EFContext()
        {
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<EFContext, Configuration>());
        }
        public EFContext() : base("DefaultConnection")
        {
        }

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

4.在資料庫添加一些測試數據

Id ProductName
21 產品1
22 產品2
23 產品3
24 產品4

5、在Controllers文件夾添加OData控制器

6、vs將自動生成基本的CURD，

將GetProducts方法的EnableQuery特性的AllowedQueryOptions屬性設置為：允許所有查詢AllowedQueryOptions.All

    public class ProductsController : ODataController
    {
        private EFContext db = new EFContext();

        // GET: odata/Products
        [EnableQuery(AllowedQueryOptions = AllowedQueryOptions.All)]
        public IQueryable<Product> GetProducts()
        {
            return db.Products;
        }

        // GET: odata/Products(5)
        [EnableQuery]
        public SingleResult<Product> GetProduct([FromODataUri] int key)
        {
            return SingleResult.Create(db.Products.Where(product => product.Id == key));
        }

        // PUT: odata/Products(5)
        public IHttpActionResult Put([FromODataUri] int key, Delta<Product> patch)
        {
            Validate(patch.GetEntity());

            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            Product product = db.Products.Find(key);
            if (product == null)
            {
                return NotFound();
            }

            patch.Put(product);

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ProductExists(key))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return Updated(product);
        }

        // POST: odata/Products
        public IHttpActionResult Post(Product product)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            db.Products.Add(product);
            db.SaveChanges();

            return Created(product);
        }

        // PATCH: odata/Products(5)
        [AcceptVerbs("PATCH", "MERGE")]
        public IHttpActionResult Patch([FromODataUri] int key, Delta<Product> patch)
        {
            Validate(patch.GetEntity());

            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            Product product = db.Products.Find(key);
            if (product == null)
            {
                return NotFound();
            }

            patch.Patch(product);

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ProductExists(key))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return Updated(product);
        }

        // DELETE: odata/Products(5)
        public IHttpActionResult Delete([FromODataUri] int key)
        {
            Product product = db.Products.Find(key);
            if (product == null)
            {
                return NotFound();
            }

            db.Products.Remove(product);
            db.SaveChanges();

            return StatusCode(HttpStatusCode.NoContent);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                db.Dispose();
            }
            base.Dispose(disposing);
        }

        private bool ProductExists(int key)
        {
            return db.Products.Count(e => e.Id == key) > 0;
        }
    }

7、在WebApiConfig類的Register方法裡面註冊OData路由

using System.Web.Http;
using System.Web.Http.OData.Builder;
using System.Web.Http.OData.Extensions;
using ODataTest.Models;

ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
builder.EntitySet<Product>("Products");
config.Routes.MapODataServiceRoute("odata", "odata", builder.GetEdmModel());

8、運行網站就可以在瀏覽器就行OData的API測試

 　　常用查詢：

　　查詢所有：http://localhost:64643/odata/Products

　　根據主鍵進行查詢：http://localhost:64643/odata/Products(22)  【22為主鍵值】

　　相等查詢：http://localhost:64643/odata/Products?$filter=ProductName eq '產品1'

      只查詢部分欄位：http://localhost:64643/odata/Products?$select=Id

　　模糊查詢（這個找了老半天）：http://localhost:64643/odata/Products?$filter=substringof('品1',ProductName) eq true  

　　還有更多的查詢，參考，http://www.odata.org/documentation/odata-version-3-0/url-conventions/ ，在mvc中使用EF和OData基本能夠滿足所有的前端查詢，有利於快速開發API查詢介面