Using lookup values in linq to entity queries - linq

Question

I'm a total LINQ noob so I guess you'll probably have a good laugh reading this question. I'm learning LINQ to create queries in LightSwitch and what I don't seem to understand is to select an entity based on a value in a lookup table. Say I want to select all employees in a table that have a job title that is picked from a related lookup table. I want the descriptive value in the lookup table for the user to pick from a list to use as a parameter in a query, not the non-descriptive id's.
Can someone point me to an article or tutorial that quickly explains this, or give me a quick answer? I AM reading books and have a Pluralsight account but since this is probably the most extensive knowledge I will need for now a simple tutorial would help me more that watching hours of videos and read thousands of pages of books.
Thanks in advance!
Edit: this is the code. As far as I know this should but won't work (red squigly line under EmployeeTitle, error says that EmployeeContract does not contain a definition for EmployeeTitle even though there is a relationship between the two).
partial void ActiveEngineers_PreprocessQuery(ref IQueryable<Employee> query)
{
query = from Employee e in query
where e.EmployeeContract.EmployeeTitle.Description == "Engineer"
select e;
}
Edit 2: This works! But why this one and not the other?
partial void ActiveContracts_PreprocessQuery(ref IQueryable<EmployeeContract> query)
{
query = from EmployeeContract e in query
where e.EmployeeTitle.Description == "Engineer"
select e;
}

Answer 1

The red squiggly line you've described is likely because each Employee can have 1-to-many EmployeeContracts. Therefore, Employee.EmployeeContracts is actually an IEnumerable<EmployeeContract>, which in turn does not have a "EmployeeTitle" property.
I think what you're looking for might be:
partial void ActiveEngineers_PreprocessQuery(ref IQueryable<Employee> query)
{
query = from Employee e in query
where e.EmployeeContract.Any(x => x.EmployeeTitle.Description == "Engineer")
select e;
}
What this is saying is that at least one of the Employee's EmployeeContracts must have an EmployeeTitle.Description == "Engineer"

Answer 2

Try something like this:
partial void RetrieveCustomer_Execute()
{
Order order = this.DataWorkspace.NorthwindData.Orders_Single
(Orders.SelectedItem.OrderID);
Customer cust = order.Customer;
//Perform some task on the customer entity.
}
(http://msdn.microsoft.com/en-us/library/ff851990.aspx#ReadingData)

Answer 3

Assuming you have navigation properties in place for the foreign key over to the lookup table, it should be something like:
var allMonkies = from employee in context.Employees
where employee.EmployeeTitle.FullTitle == "Code Monkey"
select employee;
If you don't have a navigation property, you can still get the same via 'manual' join:
var allMonkies = from employee in context.Employees
join title in context.EmployeeTitles
on employee.EmployeeTitleID equals title.ID
where title.FullTitle == "Code Monkey"
select employee;