How to build the correct LINQ query (generate OR instead of AND) - sql

Question

I need some help in building the correct query. I have an Employees table. I need to get a list of all employees, that EENO (Employee ID) contains a string from a supplied array of partial Employee IDs.
When I use this code
// IEnumerable<string> employeeIds is a collection of partial Employee IDs
IQueryable<Employee> query = Employees;
foreach (string id in employeeIds)
{
query = query.Where(e => e.EENO.Contains(id));
}
return query;
I will get something like:
SELECT *
FROM Employees
WHERE EENO LIKE '%1111111%'
AND EENO LIKE '%2222222%'
AND EENO LIKE '%3333333%'
AND EENO LIKE '%4444444%'
Which doesn't make sense.
I need "OR" instead of "AND" in resulting SQL.
Thank you!
UPDATE
This code I wrote using PredicateBuilder works perfectly when I need to include these employees.
var predicate = PredicateBuilder.False<Employee>();
foreach (string id in employeeIds)
{
var temp = id;
predicate = predicate.Or(e => e.EENO.Contains(temp));
}
var query = Employees.Where(predicate);
Now, I need to write an opposite code, to exclude these employees,
here it is but it is not working: the generated SQL is totally weird.
var predicate = PredicateBuilder.False<Employee>();
foreach (string id in employeeIds)
{
var temp = id;
predicate = predicate.And(e => !e.EENO.Contains(temp)); // changed to "And" and "!"
}
var query = Employees.Where(predicate);
return query;
It's supposed to generate SQL Where clause like this one:
WHERE EENO NOT LIKE '%11111%'
AND NOT LIKE '%22222%'
AND NOT LIKE '%33333%'
But it's not happening
The SQL generated is this: http://i.imgur.com/9MDP7.png
Any help is appreciated. Thanks.

Answer 1

Instead of the foreach, just build the IQueryable once:
query = query.Where(e => employeeIds.Contains(e.EENO));

Answer 2

I'd take a look at http://www.albahari.com/nutshell/predicatebuilder.aspx. This has a great way of building Or queries, and is written by the guy that wrote LinqPad. The above link also has examples of usage.

Answer 3

I believe you can use Any():
var query = Employees.Where(emp => employeeIds.Any(id => id.Contains(emp.EENO)));

Answer 4

If you don't want to use a predicate builder, then the only other option is to UNION each of the collections together on an intermediate query:
// IEnumerable<string> employeeIds is a collection of partial Employee IDs
IQueryable<Employee> query = Enumerable.Empty<Employee>().AsQueryable();
foreach (string id in employeeIds)
{
string tempID = id;
query = query.Union(Employees.Where(e => e.EENO.Contains(tempID));
}
return query;
Also keep in mind that closure rules are going to break your predicate and only end up filtering on your last criteria. That's why I have the tempID variable inside the foreach loop.
EDIT: So here's the compendium of all the issues you've run across:
Generate ORs instead of ANDS
Done, using PredicateBuilder.
Only last predicate is being applied
Addressed by assigning a temp variable in your inner loop (due to closure rules)
Exclusion predicates not working
You need to start with the correct base case. When you use ORs, you need to make sure you start with the false case first, that way you only include records where AT LEAST ONE predicate matches (otherwise doesn't return anything). The reason for this is that the base case should just get ignored for purposes of evaluation. In other words false || predicate1 || predicate2 || ... really is just predicate1 || predicate2 || ... because you're looking for at least one true in your list of predicates (and you just need a base to build on). The opposite applies to the AND case. You start with true so that it gets "ignored" for purposes of evaluation, but you still need a base case. In other words: true && predicate1 && ... is the same as predicate1 && .... Hope that addresses your last issue.