Passing null as Contains() within "linq to sql" query - linq

Question

I have a problem with Contains in linq to sql query as below:
public IAuditRecord[] Fetch(SearchConditions searchConditions)
{
IAuditRecord[] searchedList = (from rows in _dbContex.AuditTrails
where
(searchConditions.Owner == null || searchConditions.Owner == 0) ? true : rows.Owner == searchConditions.Owner
&&
/*This line cannot compile when ActionIDs array is empty*/
(searchConditions.ActionIDs != null && searchConditions.ActionIDs.Length != 0) ? searchConditions.ActionIDs.Contains(rows.UserActionID) : true
&& ((searchConditions.StartDate != null && searchConditions.EndDate != null) ? (rows.TimeStamp >= searchConditions.StartDate && rows.TimeStamp <= searchConditions.EndDate)
: (searchConditions.StartDate != null && searchConditions.EndDate == null) ? rows.TimeStamp >= searchConditions.StartDate : (searchConditions.StartDate == null && searchConditions.EndDate != null) ? (rows.TimeStamp <= searchConditions.EndDate)
: true)
select rows).ToArray();
return searchedList;
}
This query executes perfectly if searchCondition.ActionIDs array is not null or empty,
but when i pass the ActionIDs array as null the query cannot be compiled.
So the main question is Why contains cannot work when ActionIDs array is null?

Answer 1

You're building an IQueryable, which defines how to query for something, not actually doing it. To do this it builds an Expression, which defines all the query intents and can later be called to actually get the data. If you were using LINQ-to-Objects, this would likely work since it would likely call searchConditions.ActionIDs != null first, then know that it doesn't have to attempt to execute the second portion. Linq-to-Entities/SQL, etc. don't have that benefit.
Long story short, you can either do:
searchConditions.ActionIDs = searchConditions.ActionIDs ?? new int[];
Or do a different query if its null, like:
var query = _dbContext.AuditTrails;
if(searchConditions.ActionIDs != null && searchCondition.ActionIDs.Length != 0)
{
query = // Further filtered query where ActionIDs are taken into account.