How to query navigation property of a singleton entity?

[RonnyRen]

I want to support the following OData APIs, user is singleton, users is entity set, user has many orders, orders is entity set.
/odata/users: return info of all the users.
/odata/users({key}): return info of an user
/odata/user: return the info of current login user
/odata/orders: return all the orders
/odata/orders({key}): return an order based on the key
/odata/user/orders: return all the order of the current login user
/odata/user/orders({key}): return the order based on key of current login user

Class:
public class User
{
[Key]
public string Id { get; set; }
public string Name { get; set; }
public ICollection Orders { get; set; }
}

public class Order
{
[Key]
public int Id { get; set; }
public string UserId { get; set; }
public string ProductName { get; set; }
public User User { get; set; }
}
EDM setting
builder.EntitySet("Users");
builder.Singleton("User");
builder.EntitySet("Orders");
// Navigation: User → Orders
builder.EntityType().HasMany(u => u.Orders);

Controllers
public class UsersController : ODataController
[EnableQuery]
public IActionResult Get() //works for /odata/users
public IActionResult Get([FromODataUri] string key) //works for /odata/users({key})

public class UserController : ODataController
[EnableQuery]
public IActionResult Get() //works for /odata/user

public class OrdersController : ODataController
[EnableQuery]
public IActionResult Get() //works for /odata/orders

[EnableQuery]
public IActionResult Get([FromODataUri] int key) //works for /odata/orders({key})

I can make route /odata/user/orders working through adding method GetOrders() in Controller UserController,
how to support both route /odata/user/orders and /odata/user/orders({key}) through standard OData API?
According to the Microsoft Copilot, it says OrdersController can handle routes /odata/orders, /odata/user/orders, /odata/orders({key}) and /odata/user/orders({key}) by default based on EDM setting, but it doesn't work in my testing, does OData support this case? What extra configure is required? Thanks.

[xuzhg]

1. For the singleton, you'd setup the navigation property binding explicitly as follows: (I use 'me' as singleton name)

odataBuilder.Singleton<User>("Me").HasManyBinding(u => u.Orders, "Orders");

Then, the metadata contains

2. Then, you can build the routing to access the navigation property from singleton

The following builds an endpoint using the convention routing. It can query like: ~/odata/me/orders.

    public class MeController : Controller
    {
        [HttpGet]
        public string GetOrders() => "Hello from /me endpoint";

3. If you want to continue single order using me, like ~/odata/me/orders(4), you should use the attribute routing since no convention routing built to support this pattern.

        [ODataAttributeRouting]
        [HttpGet("odata/me/Orders({key})")]
        public string GetOrders(int key) => $"Hello from /me/orders({key}) endpoint";

Please share more questions here. Thanks.

[RonnyRen]

Thanks for your answer.
Is it possible to add a custom RoutingConvention to support route /odata/user/orders({key}) by Controller OrdersController?
One more question, how can I make navigation key working? For example: /odata/users({key})/orders({navKey}).

[xuzhg]

Thanks for your answer. Is it possible to add a custom RoutingConvention to support route /odata/user/orders({key}) by Controller OrdersController? One more question, how can I make navigation key working? For example: /odata/users({key})/orders({navKey}).

1. Yes, you can create an implementation of IODataControllerActionConvention and inject an instance into the Conventions property when calling AddOData(opt => ....)
2. You can add an action decorated with [HttpGet('odata/users({key})/orders({navKey})'].

Let me know if it cannot work.