Question

I am using RIA Services with Entity Framework in Silverlight 5. i have a following Foo table;

Fooid
FooName
FooCode
FooRef

Fooid is an auto-increment number – works like a charm on save …
FooName is set in ViewModel – works fine on save …
FooCode is a 3 letter code e.g. GRN, SIP, XYZ … this is also set in the ViewModel .. no problem
FooRef is an incrementing integer. e.g. last saved value on server is 100, now the next save should be 101.

i am a bit confused as how to get this latest number. i researched a bit and i found out two ways but i am confused using these and needs help how to implement.

First Method
from ViewModel, i can call an INVOKE from RIA Service, which can provide me the last saved FooRef int. i can add it by 1 and pass the value on SubmitChanges.
Problem with First Method : The problem i face with this method is, lets say there are 3 users at their workstations at different locations. they all start creating a new Foo, when they call invoke method, they all will be given the same value which kind of breaks the whole concept down.

Second Method
I somehow intercept the Add method on server, may be via Repository, and get the value of FooRef just before Adding this entity and submitting changes.

Onyone can help?

Answer 1

At the end, i just went on with Invoke method, and in the invoke callback function, i end up submitting the context to server.

context.GetAssignedFooRef((op =>
        {
          entityNewFoo.FooRef = op.Value; // assign return int to FooRef

          context.Foo.Add(entityNewFoo);
          context.SubmitChanges();
         }

This is how i tackle my problem, i dont know if it is an ideal solution or even close to it, but it works with me. The only problem i face is that, if there is another user seeking a FooRef from invoke before the first one saved. This is where Validation kicks in, and there i am going to request a new FooRef if there exists a same FooRef in the database.