Linq-to-SQL: ignore null parameters from WHERE clause

Question

The query below should specify records that either have the corresponding identifier specified in ownerGroupIds or the corresponding ownerUserId . However ownerUserId is null, I want this part of the request to be ignored.

    public static int NumberUnderReview(int? ownerUserId, List<int> ownerGroupIds)
    {
        return ( from c in db.Contacts
                 where 
                 c.Active == true 
                 &&
                 c.LastReviewedOn <= DateTime.Now.AddDays(-365) 
                 &&
                 ( // Owned by user
                    !ownerUserId.HasValue || 
                    c.OwnerUserId.Value == ownerUserId.Value
                 )
                 &&
                 ( // Owned by group
                    ownerGroupIds.Count == 0 ||
                    ownerGroupIds.Contains( c.OwnerGroupId.Value )
                 )
                 select c ).Count();
    }

However, when null is passed for ownerUserId , I get the following error:Nullable object must have a value.

I get a tingling sensation, may I have to use the lambda expression in this case?

Answer 1

, int, .

:

Print(null);

private void Print(int? num)
{
     Console.WriteLine(num.Value);
}

.

, :

var q = ( from c in db.Contacts
                 where 
                 c.Active == true 
                 &&
                 c.LastReviewedOn <= DateTime.Now.AddDays(-365) 
                 &&
                 ( // Owned by group
                    ownerGroupIds.Count == 0 ||
                    ownerGroupIds.Contains( c.OwnerGroupId.Value )
                 )
                 select c );

if(ownerUserId != null && ownerUserId.HasValue)
     q = q.Where(p => p.OwnerUserId.Value == ownerUserId.Value);

return q.Count();

Answer 2

OwnerUserId null? , c.OwnerUserId c.OwnerUserId.Value

Answer 3

where ?

public static int NumberUnderReview(int? ownerUserId, List<int> ownerGroupIds)
    {

    var x = ( from c in db.Contacts
                 where 
                 c.Active == true 
                 &&
                 c.LastReviewedOn <= DateTime.Now.AddDays(-365) 
                 &&
                 ( // Owned by group
                    ownerGroupIds.Count == 0 ||
                    ownerGroupIds.Contains( c.OwnerGroupId.Value )
                 )
                 select c );

    if (ownerUserId.HasValue) {
        x = from a in x
            where c.OwnerUserId.Value == ownerUserId.Value
    }

    return x.Count();
    }

Answer 4

: "& &" "||" "AndCondition (a, b)", "! a.HasValue || a.Value == b" "OrCondition (! a.HasValue, a.Value == b);" , , , , SQL. "?:".

. : http://peetbrits.wordpress.com/2008/10/18/linq-breaking-your-logic/

// New revised code.
public static int NumberUnderReview(int? ownerUserId, List<int> ownerGroupIds)
{
    return ( from c in db.Contacts
             where 
             c.Active == true 
             &&
             c.LastReviewedOn <= DateTime.Now.AddDays(-365) 
             &&
             ( // Owned by user
                // !ownerUserId.HasValue || 
                // c.OwnerUserId.Value == ownerUserId.Value
                ownerUserId.HasValue ? c.OwnerUserId.Value == ownerUserId.Value : true
             )
             &&
             ( // Owned by group
                // ownerGroupIds.Count == 0 ||
                // ownerGroupIds.Contains( c.OwnerGroupId.Value )
                ownerGroupIds.Count != 0 ? ownerGroupIds.Contains( c.OwnerGroupId.Value ) : true
             )
             select c ).Count();
}