Linq to Entities 4.0 ('Include'): In search of an elegant way

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): enter image description here

Please check this answer here http://stackoverflow.com/questions/6102909/entity-framework-include-strongly-typed#answer-10843340 — NightOwl89, Apr 16 '14 at 08:37
EF 4.0 => This is the latest distributed version within the company. — User999999, Apr 16 '14 at 08:48

Murdock · Answer 1 · 2014-04-16T08:54:08.830

4

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

edited Apr 16 '14 at 08:54

answered Apr 16 '14 at 08:35

Murdock

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found i on the internet and tried that. But the Include method accepts only a single string as parameter. Not a Lambda expression (even with adding System.Data.Entity). Or is there another namespace required? I will add a screenshot of this to my question. – User999999 Apr 16 '14 at 08:41
@svranken Are you using EF 4.1 or later? – Loetn Apr 16 '14 at 08:44
@svranken Method signature: public static IQueryable Include(this IQueryable source, Expression> path) where T : class; in QueryableExtensions in System.Data.Entity – Murdock Apr 16 '14 at 08:46
EF 4.0 => This is the latest distributed version within the company. Why are we always so far behind on the latest technologies .... – User999999 Apr 16 '14 at 08:47
@svranken sorry mate then this don't work then I suggest you go with the other answer. – Murdock Apr 16 '14 at 08:50
Thnx for the help! I'll give Alberto's solution a shot. – User999999 Apr 16 '14 at 08:51

score 2 · Accepted Answer · edited Apr 16 '14 at 09:44

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.

edited Apr 16 '14 at 09:44

User999999

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answered Apr 16 '14 at 08:35

Alberto

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You do not have to do your own extension method. Use the one built into EF – Murdock Apr 16 '14 at 08:37
This is already built-in in Entity Framework. See @Murdock's answer. – Loetn Apr 16 '14 at 08:38
In the older versions this method is not present. – Alberto Apr 16 '14 at 08:45
You are right. :) Maybe you can add this to you answer? – Loetn Apr 16 '14 at 08:48

Linq to Entities 4.0 ('Include'): In search of an elegant way

2 Answers2