使用与LINQ的SQL IN函数等效的集合

Question

How do I translate the following in LINQ?

SELECT DISTINCT w.Worker_ID, w.Surname, w.FirstName, ps.JobNumber
FROM Worker w, ProjectSignatory ps
where w.Worker_ID = ps.Worker_ID
and ps.JobNumber 
IN 
    (SELECT DISTINCT pa.JobNumber
    FROM Worker w, PAAFRegister pa
    where w.Worker_ID = pa.Worker_ID
    and w.Worker_ID = @UserX)

I have seen anumber of posts which sugges that the .Contains function is a good idea, however since I am looking through a collection of results then based from what I have seen on other responses LINQ does not like it when people call .Contains on a collection.

I am trying to understand the workings of LINQ on the whole. I am relatively inexperienced. Any advice would be greatly appreciated.

EDIT: I have seen a few approaches and I am wondering if the following is a good start or would it be best achieved using a linge query using joins?

var sig = from w in db.Workers
          join ps in db.ProjectSignatories
              on w.Worker_ID equals ps.Worker_ID
          select ps;

var paaf = from w in db.Workers
           join pa in db.PAAFRegisters
               on w.Worker_ID equals pa.Worker_ID
           where w.Worker_ID == workerID
           select w;

I am aware that this is incomplete and seves no purpose or makes no sense to what I am attempting to achieve. This was merely an example based on previous posts I have seen and wondering if the approach is suitable.

Thanks!

Answer 1

You're looking for the .Contains() function.

1. First build up the inner filter set section of the query.

   EG: The part that goes in the .Contains() (in SQL terms the " ps.JobNumber IN (...) " )

2. Filter your query by the new data subset by using the .Contains function.

Example:

C# SQL-like syntax:

var subSet = select JobNumber 
               from Workers 
              where Worker_ID == "UserX";

var result = select JobNumber 
               from Workers 
              where subSet.Contains(jobnumber);

LINQ chaining:

var subSet = Workers.Where(o => o.Worker_ID == "UserX")
                    .Select(o => o.JobNumber)
                    .Distinct();

var result = Workers.Where(o => subSet.Contains(o.JobNumber)).ToList();

Answer 2

You can create subselect's in LINQ.

var jobNumbers = select JobNumber from Workers where <your criteria, joins>
var myResult = select JobNumber from Workers where <your criteria, joins> and jobNumbers.Contains(JobNumber)