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      1. .NET Core开发日志之OData(Open Data Protocol)

         更新时间:2019年02月12日 11:22:30   作者:Ken.W   我要评论

        这篇文章主要给大家介绍了关于.NET Core开发日志之OData(Open Data Protocol)的相关资料,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友们下面来一起学习学习吧

        简述

        OData,即Open Data Protocol,是由微软在2007年推出的一款开放协议,旨在通过简单、标准的方式创建和使用查询式及交互式RESTful API。

        类库

        在.NET Core中想要使用OData功能的话需要添加Microsoft.AspNetCore.OData包。

        dotnet add package Microsoft.AspNetCore.OData

        准备模型类

        public class Address
        {
         public string City { get; set; }
         public string Street { get; set; }
        }
        public enum Category
        {
         Book,
         Magazine,
         EBook
        }
        public class Press
        {
         public int Id { get; set; }
         public string Name { get; set; }
         public string Email { get; set; }
         public Category Category { get; set; }
        }
        public class Book
        {
         public int Id { get; set; }
         public string ISBN { get; set; }
         public string Title { get; set; }
         public string Author { get; set; }
         public decimal Price { get; set; }
         public Address Address { get; set; }
         public Press Press { get; set; }
        }

        创建Edm模型

        OData使用EDM,即Entity Data Model来描述数据的结构。在Startup文件中添加创建方法。

        private static IEdmModel GetEdmModel()
        {
          var builder = new ODataConventionModelBuilder();
          builder.EntitySet<Book>("Books");
          builder.EntitySet<Press>("Presses");
          return builder.GetEdmModel();
        }

        注册OData服务

        在Startup文件的ConfigureServices方法里注册OData服务。

        services.AddOData();
        services.AddMvc(options =>
          {
            options.EnableEndpointRouting = false;
          }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

        这里要注意的是在.NET Core 2.2里,默认已经有终结点,所以要使用OData的终结点的话需要将默认选项禁用掉。

        注册OData终结点

        同样在Startup文件里,在其Configure方法内将原来的注册路由内容改为注册OData的终结点。

        app.UseMvc(b =>
        {
          b.MapODataServiceRoute("odata", "odata", GetEdmModel());
        });

        显示元数据

        运行程序后访问https://localhost:5001/odata/$metadata地址,可以看到所有可用模型的元数据。

        <edmx:Edmx xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx" Version="4.0">
          <edmx:DataServices>
            <Schema xmlns="http://docs.oasis-open.org/odata/ns/edm" Namespace="Default">
              <EntityType Name="Book">
                <Key>
                  <PropertyRef Name="Id"/>
                </Key>
                <Property Name="Id" Type="Edm.Int32" Nullable="false"/>
                <Property Name="ISBN" Type="Edm.String"/>
                <Property Name="Title" Type="Edm.String"/>
                <Property Name="Author" Type="Edm.String"/>
                <Property Name="Price" Type="Edm.Decimal" Nullable="false"/>
                <Property Name="Address" Type="Default.Address"/>
                <NavigationProperty Name="Press" Type="Default.Press"/>
              </EntityType>
              <EntityType Name="Press">
                <Key>
                  <PropertyRef Name="Id"/>
                </Key>
                <Property Name="Id" Type="Edm.Int32" Nullable="false"/>
                <Property Name="Name" Type="Edm.String"/>
                <Property Name="Email" Type="Edm.String"/>
                <Property Name="Category" Type="Default.Category" Nullable="false"/>
              </EntityType>
              <ComplexType Name="Address">
                <Property Name="City" Type="Edm.String"/>
                <Property Name="Street" Type="Edm.String"/>
              </ComplexType>
              <EnumType Name="Category">
                <Member Name="Book" Value="0"/>
                <Member Name="Magazine" Value="1"/>
                <Member Name="EBook" Value="2"/>
              </EnumType>
              <EntityContainer Name="Container">
                <EntitySet Name="Books" EntityType="Default.Book">
                  <NavigationPropertyBinding Path="Press" Target="Presses"/>
                </EntitySet>
                <EntitySet Name="Presses" EntityType="Default.Press"/>
              </EntityContainer>
            </Schema>
          </edmx:DataServices>
        </edmx:Edmx>

        创建Controller

        本文实例中不考虑数据库的操作,故而使用hard code方式构建必要的模型对象。

        public class BooksController : ODataController
        {
          private static IList<Book> Books {get; set;}
          public BooksController()
          {
            Books = new List<Book>
            {
              new Book
              {
                Id = 1,
                ISBN = "111-0-321-56789-1",
                Title = "Calculus",
                Price = 66.6m,
                Address = new Address
                {
                  City = "Shanghai",
                  Street = "Beijin Xi Road"
                },
                Press = new Press
                {
                  Id = 1,
                  Name = "Shanghai Tongji",
                  Category = Category.Book
                }
              },
              new Book
              {
                Id = 2,
                ISBN = "222-2-654-00000-2",
                Title = "Linear Algebra",
                Price = 53.2m,
                Address = new Address
                {
                  City = "Shanghai",
                  Street = "Beijin Dong Road"
                },
                Press = new Press
                {
                  Id = 2,
                  Name = "Shanghai Fudan",
                  Category = Category.EBook
                }
              }      
            };  
          }
        
          [EnableQuery]
          public IActionResult Get()
          {
            return Ok(Books);
          }
        
          [EnableQuery]
          public IActionResult Get(int key)
          {
            return Ok(Books.FirstOrDefault(b => b.Id == key));
          }
        }

        EnableQuery特性在需要高级查询的场景时必须添加。

        查询

        加入Controller之后,访问https://localhost:5001/odata/Books地址,可得到所有Book数据。

        {
          "@odata.context": "https://localhost:5001/odata/$metadata#Books",
          "value": [
            {
              "Id": 1,
              "ISBN": "111-0-321-56789-1",
              "Title": "Calculus",
              "Author": null,
              "Price": 66.6,
              "Address": {
                "City": "Shanghai",
                "Street": "Beijin Xi Road"
              }
            },
            {
              "Id": 2,
              "ISBN": "222-2-654-00000-2",
              "Title": "Linear Algebra",
              "Author": null,
              "Price": 53.2,
              "Address": {
                "City": "Shanghai",
                "Street": "Beijin Dong Road"
              }
            }
          ]
        }

        访问https://localhost:5001/odata/Books(1)地址,可得到key值为1的Book数据。

        {
          "@odata.context": "https://localhost:5001/odata/$metadata#Books/$entity",
          "Id": 1,
          "ISBN": "111-0-321-56789-1",
          "Title": "Calculus",
          "Author": null,
          "Price": 66.6,
          "Address": {
            "City": "Shanghai",
            "Street": "Beijin Xi Road"
          }
        }

        高级查询

        如果想要使用OData查询的高级功能,可以在注册终结点时额外?#30001;?#30456;应的配置。

        app.UseMvc(b =>
        {
          b.Select().Expand().Filter().OrderBy().MaxTop(100).Count();
          b.MapODataServiceRoute("odata", "odata", GetEdmModel());
        });

        访问网址时?#30001;?#25152;需的查询内容:
        https://localhost:5001/odata/Books?$select=Id,Title

        {
          "@odata.context": "https://localhost:5001/odata/$metadata#Books(Id,Title)",
          "value": [
            {
              "Id": 1,
              "Title": "Calculus"
            },
            {
              "Id": 2,
              "Title": "Linear Algebra"
            }
          ]
        }

        如果想要按特定条件过滤数据内容的话也很容易:
        https://localhost:5001/odata/Books?$filter=Price%20le%2060

        {
          "@odata.context": "https://localhost:5001/odata/$metadata#Books",
          "value": [
            {
              "Id": 2,
              "ISBN": "222-2-654-00000-2",
              "Title": "Linear Algebra",
              "Author": null,
              "Price": 53.2,
              "Address": {
                "City": "Shanghai",
                "Street": "Beijin Dong Road"
              }
            }
          ]
        }

        总结

        不难看出,OData的真正魅力在于其对那些高级查询功能的支持,所以在创建RESTful API时,不妨考虑使用OData,这样应该能减少许多不必要的代码工作。

        好了,以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,如果有疑问大家可以留言交流,谢谢大家对脚本之家的支持。

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