Linq to Entities 4.0（“包含”）：寻找一种优雅的方式

Question

I'm learning Linq to entities on my own and I have a bit of a question. Take a look at the following method. It returns the latest completed task for every item inside the List of WorkflowsInProgress . This method is being called within an other method where i'm using the fields of TasksInProgress , but i'm also using properties of the linked Tasks and WorkflowInProgress . As you will see I've added the Include to the query.

    public List<TasksInProgress> GetLatestTaskForWorkflowsInProcess(List<WorkflowInProgress> pWorkflowsInProcess)
    {
        List<TasksInProgress> tasksLst = new List<TasksInProgress>();
        List<Int64> workflowIds = pWorkflowsInProcess.Select(w => w.Id).ToList();
        using (TaskWorkflowEntities myDatacontext = new TaskWorkflowEntities())
        {

            tasksLst = (from taskP in myDatacontext.TasksInProgress.Include("Tasks").Include("WorkflowInProgress")
                        where (taskP.RunningState == (int)WorkflowRunningStates.Completed) &&
                        workflowIds.Contains(taskP.WorkflowInProgressId) &&
                        taskP.Completed == (from sTaskP in myDatacontext.TasksInProgress
                                          where sTaskP.WorkflowInProgressId == taskP.WorkflowInProgressId
                                          group sTaskP by sTaskP.WorkflowInProgressId into gSTaskP
                                          select gSTaskP.Max(g => g.Completed)).FirstOrDefault()
                        select taskP).ToList<TasksInProgress>();
        }

        return tasksLst;
    }

My Question is:

'Is there a more elegant way to include other tables inside a Query?' Because i don't like those hardcoded objectnames just sitting there' (Imagine if the tablename changes...)

Or is there any other way that i can use to include the fields of linked objects/navigational properties?

Note: Example of the methode above this one:

foreach(TasksInProgress taskInProc in _taskWorkflowS.GetLatestTaskForWorkflowsInProcess(currentWorkflowsInProcess))
{
   //Do something with (int)taskInProc.Tasks.TaskOrder
   //Do something with taskInProc.WorkflowInProgress.WorkflowId
   // ...

   //for Instance
   int i = 0;
   i = _taskWorkflowS.GetAmountOfTasksForWorkflow(taskInProc.WorkflowInProgress.WorkflowId, (int)taskInProc.Tasks.TaskOrder)

   if (i > 0 ) 
   { ... }
}

Update: using lambda expression as parameter of the Include doesn't appear to be working due to the fact that it only excepts string (see image below):

Answer 1

Edit: Answer before the question was changed to Entity Framework 4.0. This will only work for EF 4.1 and later

You can have

.Include(o => o.Tasks)

if you add

using System.Data.Entity;

at least you are not using strings then and you will get errors if the table changes

Answer 2

You can write an extension method that use a lambda expression instead of a string:

public static ObjectQuery<T> Include<T>(this ObjectQuery<T> query, Expression<Func<T, object>> selector)
{
    MemberExpression body = selector.Body as MemberExpression;
    return query.Include(body.Member.Name);

}

and use it like:

myDatacontext.TasksInProgress.Include(q=>q.Tasks)
                             .Include(q=>q.WorkflowInProgress)

I have not tested it, but it should work.