entity framework - C# linq include before-after where

Question

In linq is there a difference between:

EFDbContext _db = new EFDbContext();



  1)_db.UserQuizes
        .Where(uq => uq.UserId == currentUserId && uq.QuizId == quizId)
        .Include(qz => qz.Quiz.VerbalQuizes.Select(q => q.Question)).First()

2)_db.UserQuizes
        .Include(qz => qz.Quiz.VerbalQuizes.Select(q => q.Question))                          
        .Where(uq => uq.UserId == currentUserId && uq.QuizId == quizId).First()

   3)_db.UserQuizes
            .Include(qz => qz.Quiz.VerbalQuizes.Select(q => q.Question))
             First(uq => uq.UserId == currentUserId && uq.QuizId == quizId)

Notice that first query uses include after where and second before where, but result is the same. Also how to see actual sql query? In this particular case perfomance is my main goal, can i improve the query? i need to change two properties : UserQuizes property, and UserQuizes-> VerbalQuizes-> Question property.

Would it be better to split up it two queries or use it like as it is

Answer 1

Ordering of instructions like you've shown often won't make a difference in EF or LINQ to SQL. The query builder turns your entire LINQ statement into an abstract logical representation, and then another pass converts the logical structure into a SQL statement. So the WHERE predicates are all going to end up in the same place. The predicates inside a First() just get pushed over to the WHERE clause. The Include statements also get accumulated and projected to JOINs to include the extra columns needed to produce the included entity.

So the short answer is that EF will usually produce the most logical SQL statement regardless of the order in which you constructed your LINQ statement. If you need to tune it further, you should look at a stored procedure where you can hand-craft the SQL.