Question

I have 2 tables. 1 has entity’s, 1 per row. Another is simply a mapping table of my EntitiesID and EmployeeID. I am trying to write a LINQ method that returns all Entities from the First Table where the EntityID is in the mapping table that is filtered by the EmployeeID.

Simplified Table Structure Example
TaskTable: ID, Description, Status
TaskViewTable: ID, TaskID, EmployeeID

So I want to return all Rows from TaskTable where the ID is in a SubQuery results of TaskViewTable based on EmployeeID.

Any help on doing this in LINQ? I have a 1 to Many set up between the two tables as well. I know there are similar questions am maybe I’m dense but they didn’t seem to apply completely to what I was asking.(e.g. Linq Return Filtered Children)

Sorry forgot to show what I have so far:

IQueryable<tblTask> tTask=context.GetTable<tblTask>();
return tTask.Where(t => t.tblTasksViews.Where(v => v.EmployeeID == empID))

It, however, does not like my wherewith an unkown method Where(?)

Answer 1

Something like this should do the trick:

var tasks = tTask.Where(t => 
    tTaskView.Where(v => v.ID == empId).Select(v => v.TaskId).Contains(t.ID));

You could break up the above into two sections:

//1.) Get all task views for the employeeID and only select the mapped TaskId
var taskViews = tTaskView.Where(v => v.ID == empId).Select(v => v.TaskId); //taskViews = IEnumerable<int>

//2.) Then get all tasks from the filtered task ids  
var tasks = tTask.Where(t => taskViews.Contains(t.ID));

UPDATE

//3.) Project filtered results into IEnumerable<Task>
return tasks.Select(t => new Task() 
{ 
    ID = t.ID, 
    ActionableID = t.ActionableID, 
    StatusID = t.StatusID, 
    TypeID = t.TypeID, 
    Description = t.Description 
});

You can, of course, string everything into a nice one-liner:

public List<Task> GetTasks(int empId) 
{
    return tTask
        .Where(t => tTaskView.Where(v => v.ID == empId).Select(v => v.TaskId).Contains(t.ID))
        .Select(t => new Task() 
        { 
            ID = t.ID, 
            ActionableID = t.ActionableID, 
            StatusID = t.StatusID, 
            TypeID = t.TypeID, 
            Description = t.Description 
        }).ToList();
}