Feed Customization (ADO.NET Data Services)
Note
This topic describes new functionality in ADO.NET Data Services that is available as an update to the .NET Framework version 3.5 Service Pack 1. You can download and install the update from the Microsoft Download Center.
ADO.NET Data Services uses the Atom Publishing Protocol (AtomPub) to publish and edit Web resources. This protocol provides a standard method to serialize data, such as entities and relationships, into an XML format that can be included in the body of HTTP message. For more information, see Atom Format (ADO.NET Data Services). ADO.NET Data Services defines a default mapping between the data that is contained in entities and Atom elements.
You may have an application scenario that requires that the Atom data feed produced by the data service use standard Atom elements or custom feed elements. With ADO.NET Data Services, you can customize the Atom serialization in a data service response so that properties of an entity may be mapped to unused elements that are defined in the AtomPub protocol or to custom feed elements. You can enable feed customization by manually applying attributes to entity types in the data model. The data source provider of the data service determines how you should apply these attributes.
Note
Feed customization is only supported for AtomPub formatted feeds. Custom feeds are not returned when the JavaScript Object Notation (JSON) format is requested for the returned feed.
Important
When you define custom Atom Publishing Protocol (AtomPub) feeds, you must ensure that all entity properties that have custom mappings defined are included in the projection. When a mapped entity property is not included in the projection, data loss might occur. For more information, see Query Projections (ADO.NET Data Services).
Customizing Feeds with the Entity Framework Provider
The data model used with the Entity Framework provider is represented as XML in the .edmx file. In this case, the attributes that define custom feeds are added to the EntityType and Property elements that represent entity types and properties in the data model. These feed customization attributes are not defined in [MC-CSDL]: Conceptual Schema Definition File Format, which is the format that the Entity Framework provider uses to define the data model. Therefore, you must declare feed customization attributes in a specific schema namespace, which is defined as m="https://schemas.microsoft.com/ado/2007/08/dataservices/metadata". The following XML fragment shows feed customization attributes applied to Property elements of the Products entity type that define the ProductName and UnitsOnOrder properties.
<Property Name="ProductName" Type="String" Nullable="false"
MaxLength="40" Unicode="true" FixedLength="false"
m:FC_TargetPath="SyndicationAuthorName"
m:FC_ContentKind="text"
m:FC_KeepInContent="true"
/>
<Property Name="UnitsInStock" Type="Int16"
m:FC_TargetPath="UnitsInStock"
m:FC_NsPrefix="Northwind"
m:FC_NsUri="https://schemas.examples.microsoft.com/dataservices"
m:FC_KeepInContent="true"
/>
<Property Name="ReorderLevel" Type="Int16"
m:FC_TargetPath="UnitsInStock/@ReorderLevel"
m:FC_NsPrefix="Northwind"
m:FC_NsUri="https://schemas.examples.microsoft.com/dataservices"
m:FC_KeepInContent="false"
/>
These attributes produce the following customized data feed for the Products entity set. In the customized data feed, the ProductName property value is displayed in both in the author element and as the ProductName property element, and the UnitsOnOrder property is displayed in a custom element with its own unique namespace:
<entry xml:base="https://localhost:12345/Northwind.svc/"
xmlns:d="https://schemas.microsoft.com/ado/2007/08/dataservices"
xmlns:m="https://schemas.microsoft.com/ado/2007/08/dataservices/metadata"
xmlns="https://www.w3.org/2005/Atom">
<id>https://localhost:12345/Northwind.svc/Products(1)</id>
<title type="text" />
<updated>2009-10-02T05:09:44Z</updated>
<author>
<name>Chai</name>
</author>
<link rel="edit" title="Products" href="Products(1)" />
<link rel="https://schemas.microsoft.com/ado/2007/08/dataservices/related/Order_Details"
type="application/atom+xml;type=feed" title="Order_Details"
href="Products(1)/Order_Details" />
<category term="NorthwindModel.Products"
scheme="https://schemas.microsoft.com/ado/2007/08/dataservices/scheme" />
<content type="application/xml">
<m:properties>
<d:ProductID m:type="Edm.Int32">1</d:ProductID>
<d:ProductName>Chai</d:ProductName>
<d:UnitsInStock m:type="Edm.Int16">39</d:UnitsInStock>
<d:SupplierID m:type="Edm.Int32">1</d:SupplierID>
<d:CategoryID m:type="Edm.Int32">1</d:CategoryID>
<d:QuantityPerUnit>10 boxes x 20 bags</d:QuantityPerUnit>
<d:UnitPrice m:type="Edm.Decimal">18.0000</d:UnitPrice>
<d:UnitsOnOrder m:type="Edm.Int16">0</d:UnitsOnOrder>
<d:Discontinued m:type="Edm.Boolean">false</d:Discontinued>
</m:properties>
</content>
<Northwind:UnitsInStock
Northwind:ReorderLevel="10"
xmlns:Northwind="https://schemas.examples.microsoft.com/dataservices">39</Northwind:UnitsInStock>
</entry>
For more information, see How to: Customize Feeds with the Entity Framework Provider (ADO.NET Data Services).
Note
Because extensions to the data model are not supported by the Entity Designer, you must manually modify the XML file that contains the data model. For more information about the .edmx file that is generated by the Entity Data Model tools, see .edmx File Overview.
Custom Feed Attributes
The following table shows the XML attributes that customize feeds that you can add to the CSDL that defines the data model. These attributes are equivalent to the properties of the EntityPropertyMappingAttribute.
Note
Attribute names and values are case-sensitive. Attributes can be applied either to the EntityType element or to one or more Property elements, but not to both.
Attribute name |
Description |
|---|---|
FC_ContentKind |
Indicates the type of the content. The following keywords define syndication content types.
KeywordDescription
text The property value is displayed in the feed as text.
html The property value is displayed in the feed as HTML.
xhtml The property value is displayed in the feed as XML-formatted HTML.
This attribute is not supported when the FC_NsPrefix and FC_NsUri attributes are used. When you specify a value of xhtml for the FC_ContentKind attribute, you must ensure that the property value contains properly formatted XML. The data service returns the value without performing any transformations. You must also ensure that any XML element prefixes in the returned XML have a namespace URI and prefix defined in the mapped feed. |
FC_KeepInContent |
Indicates that the referenced property value should be included both in the content section of the feed and in the mapped location. Valid values are true and false. To make the resulting feed backward-compatible with earlier versions of ADO.NET Data Services, specify a value of true to make sure that the value is included in the content section of the feed. |
FC_NsPrefix |
The namespace prefix of the XML element in a non-syndication mapping. This attribute must be used with the FC_NsUri attribute and cannot be used with the FC_ContentKind attribute. |
FC_NsUri |
The namespace URI of the XML element in a non-syndication mapping. This attribute must be used with the FC_NsPrefix attribute and cannot be used with the FC_ContentKind attribute. |
FC_SourcePath |
The path of the property of the entity to which this feed mapping rule applies. This attribute is only supported when it is used in an EntityType element. The SourcePath() property cannot directly reference a complex type. For complex types, you must use a path expression where property names are separated by a backslash (/) character. For example, the following values are allowed for an entity type Person with an integer property Age and a complex property Address:
The SourcePath() property cannot be set to a value that contains a space or any other character that is not valid in a property name. |
FC_TargetPath |
The name of the target element of the resulting feed to map the property. This element can be an element defined by the Atom specification or a custom element. The following keywords are predefined syndication target-path values that point to specific location in a feed.
KeywordDescription
SyndicationAuthorEmail Equivalent to AuthorEmail().
SyndicationAuthorName Equivalent to AuthorName().
SyndicationAuthorUri Equivalent to AuthorUri().
SyndciationContributorEmail Equivalent to ContributorEmail().
SyndciationContributorName Equivalent to ContributorName().
SyndicationContributorUri Equivalent to ContributorUri().
SyndicationPublished Equivalent to Published().
SyndicationRights Equivalent to Rights()
SyndicationSummary Equivalent to Summary().
SyndicationTitle Equivalent to Title().
SyndicationUpdated Equivalent to Updated().
When mapping to a custom element, the target must be a path expression in which nested elements are separated by a backslash (/) and attributes are specified by an ampersand (@). In the following example, the string UnitsInStock/@ReorderLevel maps a property value to an attribute named ReorderLevel on a child element named UnitsInStock of the root entry element. When the target is a custom element name, the FC_NsPrefix and FC_NsUri attributes must also be specified. |
Customizing Feeds with the Reflection Provider
To customize feeds for a data model that was implemented by using the reflection provider, add one or more instances of the EntityPropertyMappingAttribute attribute to the classes that represent entity types in the data model. The properties of the EntityPropertyMappingAttribute class correspond to the feed customization attributes that are described in the previous section. The following is an example of the declaration of the Order type, with custom feed mapping defined for both properties.
Note
The data model for this example is defined in the topic How to: Create a Data Service Using the Reflection Provider (ADO.NET Data Services).
<EntityPropertyMappingAttribute("Customer", _
SyndicationItemProperty.AuthorName, _
SyndicationTextContentKind.Plaintext, True)> _
<EntityPropertyMapping("OrderId", _
SyndicationItemProperty.Title, _
SyndicationTextContentKind.Plaintext, False)> _
<DataServiceKeyAttribute("OrderId")> _
Public Class Order
[EntityPropertyMappingAttribute("Customer",
SyndicationItemProperty.AuthorName,
SyndicationTextContentKind.Plaintext, true)]
[EntityPropertyMapping("OrderId",
SyndicationItemProperty.Title,
SyndicationTextContentKind.Plaintext, false)]
[DataServiceKeyAttribute("OrderId")]
public class Order
These attributes produce the following customized data feed for the Orders entity set. In this customized feed, the OrderIdproperty value displays only in the title element of the entry and the Customer property value displays both in the author element and as the Customer property element:
<entry xml:base="https://localhost:12345/OrderItems.svc/"
xmlns:d="https://schemas.microsoft.com/ado/2007/08/dataservices"
xmlns:m="https://schemas.microsoft.com/ado/2007/08/dataservices/metadata"
xmlns="https://www.w3.org/2005/Atom">
<id>https://localhost:12345/OrderItems.svc/Orders(0)</id>
<title type="text">0</title>
<updated>2009-07-25T21:11:11Z</updated>
<author>
<name>Peter Franken</name>
</author>
<link rel="edit" title="Order" href="Orders(0)" />
<link rel="https://schemas.microsoft.com/ado/2007/08/dataservices/related/Items"
type="application/atom+xml;type=feed" title="Items" href="Orders(0)/Items" />
<category term="CustomDataService.Order"
scheme="https://schemas.microsoft.com/ado/2007/08/dataservices/scheme" />
<content type="application/xml">
<m:properties>
<d:Customer>Peter Franken</d:Customer>
</m:properties>
</content>
</entry>
For more information, see How to: Customize Feeds with the Reflection Provider (ADO.NET Data Services).
Customizing Feeds with the Dynamic Metadata Provider
Feed customization for a data model defined by using the dynamic metadata provider is expressed dynamically during execution by calling the AddEntityPropertyMappingAttribute(EntityPropertyMappingAttribute) on the ResourceType that represents an entity type in the data model.
Consuming Custom Feeds
When your application directly consumes an XML data feed returned by a request to the data service, it must be able to process any customized elements and attributes in the data feed. When you have implemented custom feeds in your data model, regardless of the data service provider, the $metadata endpoint returns custom feed information as custom feed attributes in the CSDL returned by the data service. When you use the Add Web Reference dialog or the datasvcutil.exe tool to generate client data service classes, the customized feed attributes are used to ensure that requests and responses to the data service are handled correctly.
See Also
Other Resources
Payload Formats (ADO.NET Data Services)