Web Api 2 - OData v3 - insert many-to-many table odata query

Question

I'm trying to insert a many-to-many table with web api odata controls.

And I' ve created controls with scaffolding odata controllers with ef. Everything is great. I can query the user table like this:

GET http://localhost:51875/odata/Users(1)?$expand=Roles

{
    "odata.metadata": "http://localhost:51875/odata/$metadata#Users/@Element",
    "Roles": [
        {
            "ID": 20,
            "Name": "Admin"
        }
    ],
    "ID": 1,
    "UserName": "user",
    "Password": "pass",
    "EnteredDate": "2017-12-07T14:55:22.24",
    "LastLoginDate": null,
    "Active": true
}

I've inserted the record 'Admin' manually. How can I add a new role for user?

I've tried,

PATCH http://localhost:51875/odata/Users(1)

{
    "Roles": [
        {
            url : "http://localhost:51875/odata/Roles(10)"
        }
    ],
}

it did not work. Can you help me?

Answer 1

Bit late perhaps but there is an answer to this, it is described on: learn.microsoft.com/...

Add the following CreateRef method to your UserController:

[AcceptVerbs("POST", "PUT")]
public IHttpActionResult CreateRef([FromODataUri] int key, string navigationProperty, [FromBody] Uri link)
{
    var user = Db.Users
            .FirstOrDefault(p => p.Id == key); //Get User by id
    if (user == null)
    {
        return NotFound();
    }

    switch (navigationProperty)
    {
        case "Roles":
            // You'll have to impement this 'getkey' method somehow.
            // You could implement it yourself or take a look on the webpage I linked earlier.
            var relatedKey = GetKeyFromUri(link);
            var role = Db.Roles
                    .FirstOrDefault(f => f.Id == relatedKey); //Get Role by id
            if (role == null)
            {
                return NotFound();
            }

            user.Roles.Add(role);
            break;

        default:
            return StatusCode(HttpStatusCode.NotImplemented);
    }
    Db.SaveChanges();
    return StatusCode(HttpStatusCode.NoContent);
}

Now you can add roles to a user with the following HTTP request:

PUT [...]/api/User(2)/Roles/$ref
Content-Type: application/json
Content-Length: 54
{ "@odata.id": "[...]/api/Role(4)/" }

Personally I don't find this method particularly nice but it is the standard. You could also do this with a custom 'AddRoles' action as you mention in your comment.