Question

We are trying to develop our own EF provider for our legacy APIs. We managed to get “GET/POST” operation working successfully.

However, for operation “PUT/MERGE”, the method “CreateDbCommandDefinition” (of DbProviderServices implementation) fires twice. One with “DbQueryCommandTree” and another with “DbUpdateCommandTree”.

I understand that it needs to fetch the entity prior to update it (for change tracking I guess). In our case, I don’t need the entity information to be fetched prior to update. I simply want to call our legacy APIs with the entity sent for update. How can we strictly ask it to not to do the work of “DbQueryCommandTree” (and do only the work of “DbUpdateCommandTree”) when I working with “PUT/MERGE” operations.

The client code looks something like the one below:

public void CustomerUpdateTest()
{
    try
    {
        Ctxt.MergeOption = MergeOption.NoTracking;
        var oNewCus = new Customer()
        {
            MasterCustomerId = "1001",
            SubCustomerId = "0",
            FirstName = "abc",
            LastName = "123"
        };
        Ctxt.AttachTo("Customers", oNewCus);
        Ctxt.UpdateObject(oNewCus);
        //Ctxt.SaveChanges();
        Ctxt.SaveChanges(SaveChangesOptions.ReplaceOnUpdate);
    }
    catch (Exception ex)
    {
        Assert.Fail(ex.Message);
    }

Answer 1

You will have to write your own IDataServiceUpdateProvider to make this happen. For EF, the in built EF update provider does 2 queries – one to get the entity which needs to be modified and one for the actual modification. We are planning to make this provider public in our next release, so folks can derive from it and just override one or more methods. But for now, you will have to implement the interface yourself.

For PUT/MERGE requests, WCF Data Services calls IDataServiceUpdateProvider.GetResource to get the entity to update. In your implementation of this method, you can return a token that represents the object that need to get modified (you will have to visit the expression tree that gets passed in this method to find out the entity set and the key value of the entity in question).

In SaveChanges, you can push the update based on the token. That way you can avoid one round trip to the database.

Hope this helps.