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Web API OData Routing Conventions

By Mike Wasson|
This article describes the routing conventions that Web API uses for OData endpoints.

When Web API gets an OData request, it maps the request to a controller name and an action name. The mapping is based on the HTTP method and the URI. For example, GET /odata/Products(1) maps to ProductsController.GetProduct.

In part 1 of this article, I describe the built-in OData routing conventions. These conventions are designed specifically for OData endpoints, and they replace the default Web API routing system. (The replacement happens when you call MapODataRoute.)

In part 2, I show how to add custom routing conventions. Currently the built-in conventions do not cover the entire range of OData URIs, but you can extend them to handle additional cases.

Built-in Routing Conventions

Before I describe the OData routing conventions in Web API, it’s helpful to understand OData URIs. An OData URI consists of:

  • The service root
  • The resource path
  • Query options

For routing, the important part is the resource path. The resource path is divided into segments. For example, /Products(1)/Supplier has three segments:

  • Products refers to an entity set named “Products”.
  • 1 is an entity key, selecting a single entity from the set.
  • Supplier is a navigation property that selects a related entity.

So this path picks out the supplier of product 1.

OData path segments do not always correspond to URI segments. For example, “1” is considered a path segment.

Controller Names. The controller name is always derived from the entity set at the root of the resource path. For example, if the resource path is /Products(1)/Supplier, Web API looks for a controller named ProductsController.

Action Names. Action names are derived from the path segments plus the entity data model (EDM), as listed in the following tables. In some cases, you have two choices for the action name. For example, “Get” or "GetProducts".

Querying Entities

RequestExample URIAction NameExample Action
GET /entityset/ProductsGetEntitySet or GetGetProducts
GET /entityset(key)/Products(1)GetEntityType or GetGetProduct
GET /entityset(key)/cast/Products(1)/Models.BookGetEntityType or GetGetBook

For more information, see Create a Read-Only OData Endpoint.

Creating, Updating, and Deleting Entities

RequestExample URIAction NameExample Action
POST /entityset/ProductsPostEntityType or PostPostProduct
PUT /entityset(key)/Products(1)PutEntityType or PutPutProduct
PUT /entityset(key)/cast/Products(1)/Models.BookPutEntityType or PutPutBook
PATCH /entityset(key)
/Products(1)PatchEntityType or PatchPatchProduct
PATCH /entityset(key)/cast/Products(1)/Models.BookPatchEntityType or PatchPatchBook
DELETE /entityset(key)/Products(1)DeleteEntityType or DeleteDeleteProduct
DELETE /entityset(key)/cast/Products(1)/Models.BookDeleteEntityType or DeleteDeleteBook

For more information, see Supporting OData CRUD Operations.

Querying a Navigation Property

RequestExample URIAction NameExample Action
GET /entityset(key)/navigation/Products(1)/SupplierGetNavigationFromEntityType or GetNavigationGetSupplierFromProduct
GET /entityset(key)/cast/navigation/Products(1)/Models.Book/AuthorGetNavigationFromEntityType or GetNavigationGetAuthorFromBook

For more information, see Working with Entity Relations.

Creating and Deleting Links

RequestExample URIAction Name
POST /entityset(key)/$links/navigation/Products(1)/$links/SupplierCreateLink
PUT /entityset(key)/$links/navigation/Products(1)/$links/SupplierCreateLink
DELETE /entityset(key)/$links/navigation/Products(1)/$links/SupplierDeleteLink
DELETE /entityset(key)/$links/navigation(relatedKey)/Products/(1)/$links/Suppliers(1)DeleteLink

For more information, see Working with Entity Relations.

Properties

Requires Web API 2

RequestExample URIAction NameExample Action
GET /entityset(key)/property/Products(1)/NameGetPropertyFromEntityType or GetPropertyGetNameFromProduct
GET /entityset(key)/cast/property/Products(1)/Models.Book/AuthorGetPropertyFromEntityType or GetPropertyGetTitleFromBook

Actions

RequestExample URIAction NameExample Action
POST /entityset(key)/action/Products(1)/RateActionNameOnEntityType or ActionNameRateOnProduct
POST /entityset(key)/cast/action/Products(1)/Models.Book/CheckOutActionNameOnEntityType or ActionNameCheckOutOnBook

For more information, see OData Actions.

Method Signatures

Here are some rules for the method signatures:

  • If the path contains a key, the action should have a parameter named key.
  • If the path contains a key into a navigation property, the action should have a parameter named relatedKey.
  • Decorate key and relatedKey parameters with the [FromODataUri] parameter.
  • POST and PUT requests take a parameter of the entity type.
  • PATCH requests take a parameter of type Delta, where T is the entity type.

For reference, here is an example that shows method signatures for every built-in OData routing convention.

public class ProductsController : ODataController
{
    // GET /odata/Products
    public IQueryable<Product> Get()

    // GET /odata/Products(1)
    public Product Get([FromODataUri] int key)

    // GET /odata/Products(1)/ODataRouting.Models.Book
    public Book GetBook([FromODataUri] int key)

    // POST /odata/Products 
    public HttpResponseMessage Post(Product item)

    // PUT /odata/Products(1)
    public HttpResponseMessage Put([FromODataUri] int key, Product item)

    // PATCH /odata/Products(1)
    public HttpResponseMessage Patch([FromODataUri] int key, Delta<Product> item)

    // DELETE /odata/Products(1)
    public HttpResponseMessage Delete([FromODataUri] int key)

    // PUT /odata/Products(1)/ODataRouting.Models.Book
    public HttpResponseMessage PutBook([FromODataUri] int key, Book item)

    // PATCH /odata/Products(1)/ODataRouting.Models.Book
    public HttpResponseMessage PatchBook([FromODataUri] int key, Delta<Book> item)

    // DELETE /odata/Products(1)/ODataRouting.Models.Book
    public HttpResponseMessage DeleteBook([FromODataUri] int key)

    //  GET /odata/Products(1)/Supplier
    public Supplier GetSupplierFromProduct([FromODataUri] int key)

    // GET /odata/Products(1)/ODataRouting.Models.Book/Author
    public Author GetAuthorFromBook([FromODataUri] int key)

    // POST /odata/Products(1)/$links/Supplier
    public HttpResponseMessage CreateLink([FromODataUri] int key, 
        string navigationProperty, [FromBody] Uri link)

    // DELETE /odata/Products(1)/$links/Supplier
    public HttpResponseMessage DeleteLink([FromODataUri] int key, 
        string navigationProperty, [FromBody] Uri link)

    // DELETE /odata/Products(1)/$links/Parts(1)
    public HttpResponseMessage DeleteLink([FromODataUri] int key, string relatedKey, string navigationProperty)

    // GET odata/Products(1)/Name
    // GET odata/Products(1)/Name/$value
    public HttpResponseMessage GetNameFromProduct([FromODataUri] int key)

    // GET /odata/Products(1)/ODataRouting.Models.Book/Title
    // GET /odata/Products(1)/ODataRouting.Models.Book/Title/$value
    public HttpResponseMessage GetTitleFromBook([FromODataUri] int key)
}

Custom Routing Conventions

Currently the built-in conventions do not cover all possible OData URIs. You can add new conventions by implementing the IODataRoutingConvention interface. This interface has two methods:

string SelectController(ODataPath odataPath, HttpRequestMessage request);
string SelectAction(ODataPath odataPath, HttpControllerContext controllerContext, 
    ILookup<string, HttpActionDescriptor> actionMap);
  • SelectController returns the name of the controller.
  • SelectAction returns the name of the action.

For both methods, if the convention does not apply to that request, the method should return null.

The ODataPath parameter represents the parsed OData resource path. It contains a list of ODataPathSegment instances, one for each segment of the resource path. ODataPathSegment is an abstract class; each segment type is represented by a class that derives from ODataPathSegment.

The ODataPath.TemplatePath property is a string that represents the concatenation all of the path segments. For example, if the URI is /Products(1)/Supplier, the path template is "~/entityset/key/navigation". Notice that the segments don’t correspond directly to URI segments. For example, the entity key (1) is represented as its own ODataPathSegment.

Typically, an implementation of IODataRoutingConvention does the following:

  1. Compare the path template to see if this convention applies to the current request. If it does not apply, return null.
  2. If the convention applies, use properties of the ODataPathSegment instances to derive controller and action names.
  3. For actions, add any values to the route dictionary that should bind to the action parameters (typically entity keys).

Let's look at a specific example. The built-in routing conventions do not support indexing into a navigation collection. In other words, there is no convention for URIs like the following:

/odata/Products(1)/Suppliers(1)

Here is a custom routing convention to handle this type of query.

using Microsoft.Data.Edm;
using System.Linq;
using System.Net.Http;
using System.Web.Http.Controllers;
using System.Web.Http.OData.Routing;
using System.Web.Http.OData.Routing.Conventions;

namespace ODataRouting
{
    public class NavigationIndexRoutingConvention : EntitySetRoutingConvention
    {
        public override string SelectAction(ODataPath odataPath, HttpControllerContext context, 
            ILookup<string, HttpActionDescriptor> actionMap)
        {
            if (context.Request.Method == HttpMethod.Get && 
                odataPath.PathTemplate == "~/entityset/key/navigation/key")
            {
                NavigationPathSegment navigationSegment = odataPath.Segments[2] as NavigationPathSegment;
                IEdmNavigationProperty navigationProperty = navigationSegment.NavigationProperty.Partner;
                IEdmEntityType declaringType = navigationProperty.DeclaringType as IEdmEntityType;

                string actionName = "Get" + declaringType.Name;
                if (actionMap.Contains(actionName))
                {
                    // Add keys to route data, so they will bind to action parameters.
                    KeyValuePathSegment keyValueSegment = odataPath.Segments[1] as KeyValuePathSegment;
                    context.RouteData.Values[ODataRouteConstants.Key] = keyValueSegment.Value;

                    KeyValuePathSegment relatedKeySegment = odataPath.Segments[3] as KeyValuePathSegment;
                    context.RouteData.Values[ODataRouteConstants.RelatedKey] = relatedKeySegment.Value;

                    return actionName;
                }
            }
            // Not a match.
            return null;
        }
    }
}

Notes:

  1. I derive from EntitySetRoutingConvention, because the SelectController method in that class is appropriate for this new routing convention. That means I don't need to re-implement SelectController.
  2. The convention applies only to GET requests, and only when the path template is "~/entityset/key/navigation/key".
  3. The action name is "Get{EntityType}", where {EntityType} is the type of the navigation collection. For example, "GetSupplier". You can use any naming convention that you like — just make sure your controller actions match.
  4. The action takes two parameters named key and relatedKey. (For a list of some predefined parameter names, see ODataRouteConstants.)

The next step is adding the new convention to the list of routing conventions. This happens during configuration, as shown in the following code:

using ODataRouting.Models;
using System.Web.Http;
using System.Web.Http.OData.Builder;
using System.Web.Http.OData.Routing;
using System.Web.Http.OData.Routing.Conventions;

namespace ODataRouting
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            ODataModelBuilder modelBuilder = new ODataConventionModelBuilder();
            // Create EDM (not shown).

            // Create the default collection of built-in conventions.
            var conventions = ODataRoutingConventions.CreateDefault();
            // Insert the custom convention at the start of the collection.
            conventions.Insert(0, new NavigationIndexRoutingConvention());

            config.Routes.MapODataRoute(routeName: "ODataRoute",
                routePrefix: "odata",
                model: modelBuilder.GetEdmModel(),
                pathHandler: new DefaultODataPathHandler(),
                routingConventions: conventions);

        }
    }
}

Here are some other sample routing conventions that be useful to study:

And of course Web API itself is open-source, so you can see the source code for the built-in routing conventions. These are defined in the System.Web.Http.OData.Routing.Conventions namespace.

This article was originally created on July 31, 2013

Author Information

Mike Wasson

Mike Wasson – Mike Wasson is a programmer-writer at Microsoft.