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.NET Core开发日志——OData

Ken.W 2019-02-10 21:55:00 阅读数:139 评论数:0 点赞数:0 收藏数:0

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?$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。

版权声明
本文为[Ken.W]所创,转载请带上原文链接,感谢
https://www.cnblogs.com/kenwoo/p/10360260.html

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