Reference By Value for integer doesn’t work in entity framework / LINQ query

 

Just find an interesting bugs, where I thought reference by value (int) can be used in entity framework or linq query.

Here is the code

lst = new List<IQueryable<tblProduct>>();
 int choiceID = 30;
 lst.Add(from t in originalQuery
         where t.tblProductChoiceTag.Any(c => c.ChoiceID == choiceID)
         select t);
 choiceID = 31;
 lst.Add(from t in originalQuery
         where t.tblProductChoiceTag.Any(c => c.ChoiceID == choiceID)
         select t);
       

            IQueryable<tblProduct> q = null;

            bool first = true;
            foreach (var tquery in lst)
            {
                if (first)
                {
                    q = tquery;
                    first = false;
                }
                else
                {   //the next one combine it
                    q = q.Union(tquery);
                }

            }

When it executed, linq query will use the last choiceID (31) and override (30).

This really weird, because I thought It is saved to use the same (int) variable because it will pass by value.

---

Here is another example

var q = (from t in DBHelper.Instance.tblProductVariation
                    where t.ProductID == pid
                    && t.tblChoice.Count == choices.Count
                    select t);

            foreach (var c in choices)
            {
                q = (from t in q
                     where t.tblChoice.Any(ch=>ch.ChoiceID == c.ChoiceID)
                     select t);
            }
              a
            return q.FirstOrDefault();

See on this query which the value will be iterating from the choice object

q = (from t in q
where t.tblChoice.Any(ch=>ch.ChoiceID == c.ChoiceID)
select t);

this code will pass the same value of choiceID.


To fix this you need to change it into local variable.

var cid = c.ChoiceID;

q = (from t in q
where t.tblChoice.Any(ch=>ch.ChoiceID == cid)
select t);

Anyone can explain this ?