[转]WCF Data Services OData

http://martinwilley.com/net/data/wcfds.html

WCF Data Services

• About
• OData
• Server code
• Client

For .net 4.5, this is replaced by Microsoft.AspNet.Odata which uses ODataController (based on WebApi ApiController).

About

Formerly "Astoria" and "ADO.Net Data Services", this is the .Net ODATA implementation - ODATA being RESTful HTTP/JSON/ATOM xml access to databases.

OData

HTTP verbs: GET is get, POST is insert, PUT is update, MERGE is partial update, DELETE is delete

NB: PUT,MERGE and DELETE may be blocked by proxies/firewalls, so add the X-HTTP-Method header can be added to a POST request

• Use http://localhost/wcfds.svc/$metadata to get metadata (like ?wsdl)
• http://localhost/wcfds.svc/customers(‘ALFKI‘)
  get by primary key
• http://localhost/wcfds.svc/customers/$count
• http://localhost/wcfds.svc/customers?$orderby=Price desc
• http://localhost/wcfds.svc/customers?$skip=20&$top=5
• http://localhost/wcfds.svc/customers?$filter= Name eq ‘Bill‘ and Price gt 10
• http://localhost/wcfds.svc/customers?$filter= startswith(name, ‘B‘) and year(Date) gt 2011 and round(Price) = 5
• http://localhost/wcfds.svc/customers?$expand=Orders/Order_Details
  Eager loading

Server code

Reference System.Data.Services.Client.dll. The VS2010 item template for the endpoint is "WCF Data Service". The svc code behind is a DataService<T> with a static InitializeService() method which should expose a IQueryable<T> getter.

DataService<T> can be an Entity Framework ObjectContext, which exposes the ObjectSets (tables).

For custom classes that are exposed, add a [DataServiceKeyAttribute(pk)] to the class to denote the primary key (for http://localhost/wcfds.svc/custom(‘ALFKI‘) gets). For POCOs, add [DataContract(IsReference=true)] so properties are serialized as objects, not values (i.e. product.Category refers to a Category object).

Security

You can secure with the standard IIS/web.config settings including Windows, asp.net forms etc.

In the client library, you can set context.Credentials = new NetworkCredential(username, password) or use the context.SendingRequest event to set request headers such as Authorization.

In server InitializeService, configure SetEntitySetAccessRules

Service Operations

In InitializeService, config.SetServiceOperationAccessRule("*", ServiceOperationRights.All); as applicable/

Expose sprocs as service operations: [WebGet]/[WebInvoke] methods- input parameters must be primitives, return must be primitive or IEnumerables/IQueryable.

Client

Adding a service reference to an ODATA service creates a proxy derived from DataServiceContext which looks like a normal EF ObjectContext. (MSDN concepts)

• context.SaveChanges(SaveChangesOption.Batch) will batch changes (also: ContinueOnError, ReplaceOnUpdate)
  Catch DataServiceQueryException, DataServiceRequestException
• It uses ATOM - to use JSON, use a WebClient with client.Headers["Accept"] = "application/json"
• In a partial class, add [QueryInterceptor("Customers")]public Expression... OnQueryCustomers()
• [ChangeInterceptor("Customers")] can also be used for validation (or subscribe to regular EntityChanging event)

For data-binding, wrap the objectsets in DataServiceCollection which extends ObservableCollection.

Queries

• The entity collections (ObjectSets in EF) are DataServiceQuery<T> but otherwise it‘s mostly normal IQueryable
• Eager load (ODATA $expand) with context.Orders.Expand("Order_Details")
• Explicit load (lazy load) with context.LoadProperty(order, "Order_Details")
• Explicitly executing the query returns a QueryOperationResponse.
  When paging, this has a GetContinuation property which includes the url of the next page
  NB: you must iterate the query result to use the continuation