Question

Is this linq query efficient?

    var qry = ((from member in this.ObjectContext.TreeMembers.Where(m => m.UserId == userId && m.Birthdate == null)
              select member.TreeMemberId).Except(from item in this.ObjectContext.FamilyEvents select item.TreeMemberId));


    var mainQry = from mainMember in this.ObjectContext.TreeMembers
                  where qry.Contains(mainMember.TreeMemberId)
                  select mainMember;

Will this be translated into multiple sql calls or just one? Can it be optimised? Basically I have 2 tables, I want to select those records from table1 where datetime is null and that record should not exist in table2.

Answer 1

The easiest way to find out if the query will make multiple calls is to set the .Log property of the data context. I typically set it to write to a DebugOutputWriter. A good example for this kind of class can be found here.

For a general way of thinking about it however, if you use a property of your class that does not directly map to a database field in a where clause or a join clause, it will typically make multiple calls. From what you have provided, it looks like this is not the case for your scenario, but I can’t absolutely certain and suggest using the method listed above.