I have the following straightforward case where a client communicates with .NET Web API:

1. Client makes a request for an object to the Web API giving the requested ID.
2. Web API returns the object to the client.
3. Client changes several properties of the object.
4. Client sends back the object (not the changed properties) to the Web API using PUT method.
5. Web API has to use Entity Framework to update the database.

I am not able to get step 5 implemented.
Here is the code I am using:

[HttpPut]
[ActionName("Update")]
public IHttpActionResult Update(MyModel myModel)
{
    this.context.MyModel.Attach(myModel);
    this.context.SubmitChanges();
    
    return Ok();
}

This code does not work.
We also know that the endpoints of WebAPI are stateless.

I have seen other solutions like this:

[HttpPut]
[ActionName("Update")]
public IHttpActionResult Update(MyModel myModel)
{
    this.context.MyModel.Add(myModel);
    this.context.Entry(myModel).State = System.Data.Entity.EntityState.Modified;
    this.context.SaveChanges();
    return Ok();
}

But the problem with this code is that I am using System.Data.Linq.DataContext which does not have the property Entry.
Is there a way to do that using System.Data.Linq.DataContext?