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加上相应的配置。

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

访问网址时加上所需的查询内容:
https://localhost:5001/odata/Books"htmlcode">

{
  "@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"htmlcode">

{
  "@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,谢谢大家对的支持。

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.net,core,日志,.net,core,odata,.net,core,框架

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