Linq to Entities many-to-many join
My first time using the Entity Framework so I'm not sure if I'm doing this right.

I have 4 tables:

    CustomerOrder
    ------------
    ID, StaffID, DeptID, Status, other columns...

    Staff
    ------------
    StaffID, other columns...

    StaffDept
    ------------
    StaffID, DeptID - only 2 fields

    Dept
    ------------
    DeptID, other columns...

A staff member can belong to multiple departments. The `StaffDept` table is just for storing this many-to-many relationship.<br /><br />

I need to retrieve a combination of: 

+ all Customer Orders that **don't** have a `Status` of "In Progress"
+ any extra records for the current Staff member with a `Status` of "In Progress"
+ any extra records with a `Status` of "In Progress" where the Staff member is a member of the same department as the Customer Order.

for example if I have the following data:

    Staff
    -----
    1, Mr X, ...
    2, Mr Y, ...

    Dept
    -----
    1, Sales, ...
    2, Marketing, ...

    StaffDept
    -----
    1, 1
    1, 2
    2, 2

    CustomerOrder
    -----
    1, 1, 1, In Progress, ...
    2, 1, 1, Completed, ...
    3, 2, 2, In Progress, ...
    4, 2, NULL, In Progress, ...

I would expect if the current user was #1 they would see customer orders 1,2,3. User #2 would see 2,3,4.
<br /><br />
Here is the code I have so far:

    from co in CustomerOrders
    where co.Status != "In Progress" 
      || co.StaffID == @CurrentStaffID
      || (co.StaffID != @CurrentStaffID 
          && co.DeptID!= null 
          && Staffs.Where(x => x.StaffID == @CurrentStaffID).FirstOrDefault().Depts.Any(x => x.DeptID== co.DeptID))
    select new CustomerOrderObject
    {
        Description = co.Description,
        Amount = co.Amount,
        ...
    }

which works, but Resharper complains that the FirstOrDefault() part will throw a NULL exception at runtime. I've tested with a User of #3 (which doesn't exist) in Linqpad and it doesn't throw an error - it returns just record 2 which is what I would expect. Resharper wants me to pull the `Staffs.Where(x => x.StaffID == 3).FirstOrDefault()` out into a separate query run before the query above, but I'm thinking that will make it slower? I'm really not sure that any of this query is the fastest way to get the data as I'm new to linq to entities, I've been using linq-to-sql. Any advice would be greatly appreciated - I'm not even sure how to correctly describe the type of join I'm trying to do.
Linq to Entities many-to-many join
===

My first time using the Entity Framework so I'm not sure if I'm doing this right.

I have 4 tables:

    CustomerOrder
    ------------
    ID, StaffID, DeptID, Status, other columns...

    Staff
    ------------
    StaffID, other columns...

    StaffDept
    ------------
    StaffID, DeptID - only 2 fields

    Dept
    ------------
    DeptID, other columns...

A staff member can belong to multiple departments. The `StaffDept` table is just for storing this many-to-many relationship.<br /><br />

I need to retrieve a combination of: 

+ all Customer Orders that **don't** have a `Status` of "In Progress"
+ any extra records for the current Staff member with a `Status` of "In Progress"
+ any extra records with a `Status` of "In Progress" where the Staff member is a member of the same department as the Customer Order.

for example if I have the following data:

    Staff
    -----
    1, Mr X, ...
    2, Mr Y, ...

    Dept
    -----
    1, Sales, ...
    2, Marketing, ...

    StaffDept
    -----
    1, 1
    1, 2
    2, 2

    CustomerOrder
    -----
    1, 1, 1, In Progress, ...
    2, 1, 1, Completed, ...
    3, 2, 2, In Progress, ...
    4, 2, NULL, In Progress, ...

I would expect if the current user was #1 they would see customer orders 1,2,3. User #2 would see 2,3,4.
<br /><br />
Here is the code I have so far:

    from co in CustomerOrders
    where co.Status != "In Progress" 
      || co.StaffID == @CurrentStaffID
      || (co.StaffID != @CurrentStaffID 
          && co.DeptID!= null 
          && Staffs.Where(x => x.StaffID == @CurrentStaffID).FirstOrDefault().Depts.Any(x => x.DeptID== co.DeptID))
    select new CustomerOrderObject
    {
        Description = co.Description,
        Amount = co.Amount,
        ...
    }

which works, but Resharper complains that the FirstOrDefault() part will throw a NULL exception at runtime. I've tested with a User of #3 (which doesn't exist) in Linqpad and it doesn't throw an error - it returns just record 2 which is what I would expect. Resharper wants me to pull the `Staffs.Where(x => x.StaffID == 3).FirstOrDefault()` out into a separate query run before the query above, but I'm thinking that will make it slower? I'm really not sure that any of this query is the fastest way to get the data as I'm new to linq to entities, I've been using linq-to-sql. Any advice would be greatly appreciated - I'm not even sure how to correctly describe the type of join I'm trying to do.