Building a LINQ query programmatically without local variables tricking me

Question

Assume my objects are in perfect working order (i.e. TDD makes me think they work).

I have a list that I create like this (except indented properly):

Answer 1

(Edited for clarity.)

The problem is the foreach loop, and the fact that the "a" variable is being captured and then changed each time. Here's a modification which will work, by effectively introducing a "new" variable for each iteration of the loop, and capturing that new variable.

foreach (Attribute a in requiredAttributes)
{
    Attribute copy = a;
    result = result.Where(p => p.Attributes.Contains(copy));
}

Omer's solution is a cleaner one if you can use it, but this may help if your real code is actually more complicated :)

EDIT: There's more about the issue in this closures article - scroll down to "Comparing capture strategies: complexity vs power".

Answer 2

var result = from v in vendors
             from p in v.Products
             where requiredAttributes.All(a => p.Attributes.Contains(a))
             orderby p.Name
             select p;

HTH.

Answer 3

I haven't coded it up, but change

foreach (Attribute a in requiredAttributes){    
    result = result.Where(p => p.Attributes.Contains(a));
}

to

foreach (Attribute a in requiredAttributes){    
    Attribute b = a;
    result = result.Where(p => p.Attributes.Contains(b));
}

should fix it too, I think.