Exam 70-487 topic 1 question 68 discussion

Actual exam question from Microsoft's 70-487

Question #: 68
Topic #: 1

You are developing an order processing application that uses the Entity Framework against a SQL Server database. Lazy loading has been disabled. The application displays orders and their associated order details. Order details are filtered based on the category of the product in each order.

You need to return orders with their filtered list of order details included in a single round trip to the database.
Which code segment should you use?
A.

B.

C.

D.

C -

Show Suggested Answer

Suggested Answer: Explanation
Eager loading is the process whereby a query for one type of entity also loads related entities as part of the query. Eager loading is achieved by use of the Include method. For example, the queries below will load blogs and all the posts related to each blog. using (var context = new BloggingContext())
{
// Load all blogs and related posts
var blogs1 = context.Blogs
.Include(b => b.Posts)
.ToList();
It is also possible to eagerly load multiple levels of related entities.
References:
https://msdn.microsoft.com/en-us/library/jj574232(v=vs.113).aspx

by bobtables at Nov. 26, 2019, 3:43 a.m.

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dosper

Highly Voted 5 years, 6 months ago

correct is B

upvoted 5 times

dosper

5 years, 6 months ago

It's A, the question mentions "return orders with their filtered list of order details" so with A when you do the .ToList() the engine will get all this info, with B it will only get the Orders without the details. So answer it's A

upvoted 20 times

tiger25

5 years, 4 months ago

Correct, answer is A. If B there will be multiple round trips when we try get OrderDetails info.

upvoted 4 times

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Dreamchaser1980

4 years, 8 months ago

Answer A is correct. I verified it on my computer using EF Core, Answer A results in one query executed on the database. The result is a list of orders and its corresponding order details. Note the query is executed when you call ToList(), the final Select(r => r.Order) statement is done client side, which results in a IEnumerable<Order> list.

upvoted 7 times

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UweJ

Most Recent 5 years, 1 month ago

I have tried all 4 answers in Visual Studio. None of these 4 produces the described result.

upvoted 3 times

UweJ

5 years, 1 month ago

This would in my opinion delviver what was asked for; var orders = db.Orders.Select(o => new { order = o, filteredOrderDetails = o.OrderDetails.Where(od => od.Product.Category.CategoryName == categoryName) }).ToList();

upvoted 2 times

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