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。
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dotnet add package Microsoft.AspNetCore.OData
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准备模型类
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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 ; }
}
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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。
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private static IEdmModel GetEdmModel()
{
var builder = new ODataConventionModelBuilder();
builder.EntitySet<Book>( "Books" );
builder.EntitySet<Press>( "Presses" );
return builder.GetEdmModel();
}
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注册OData服务
在Startup文件的ConfigureServices方法里注册OData服务。
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services.AddOData();
services.AddMvc(options =>
{
options.EnableEndpointRouting = false ;
}).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
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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。
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app.UseMvc(b =>
{
b.MapODataServiceRoute( "odata" , "odata" , GetEdmModel());
});
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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。
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< 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 >
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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。
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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));
}
}
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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。
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{
"@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"
}
}
]
}
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访问https://localhost:5001/odata/Books(1)地址,可得到key值为1的Book数据。
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{
"@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"
}
}
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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。
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app.UseMvc(b =>
{
b.Select().Expand().Filter().OrderBy().MaxTop(100).Count();
b.MapODataServiceRoute( "odata" , "odata" , GetEdmModel());
});
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访问网址时加上所需的查询内容:
https://localhost:5001/odata/Books?$select=Id,Title
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{
"@odata.context" : "https://localhost:5001/odata/$metadata#Books(Id,Title)" ,
"value" : [
{
"Id" : 1,
"Title" : "Calculus"
},
{
"Id" : 2,
"Title" : "Linear Algebra"
}
]
}
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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?$filter=Price%20le%2060
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{
"@odata.context" : "https://localhost:5001/odata/$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"
}
}
]
}
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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,谢谢大家对服务器之家的支持。
原文链接:https://www.cnblogs.com/kenwoo/p/10360260.html