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Exam 70-487 topic 2 question 8 discussion

Actual exam question from Microsoft's 70-487

Question #: 8
Topic #: 2

You are adding a new REST service endpoint to the FlightDataController controller. It returns flights from the consolidated data sources only for flights that are late.
You need to write a LINQ to Entities query to extract the required data.
Which code segment should you use?

A. Option A
B. Option B
C. Option C
D. Option D D

Show Suggested Answer

Suggested Answer: Explanation 🗳️

by Naveenvarma at Jan. 5, 2020, 6:11 a.m.

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tiger25

Highly Voted 5 years, 4 months ago

Answer A. We don't need extract all the FlightInfo but only WasLate history so we use IQueryable.

upvoted 19 times

Karel_Gott

5 years, 3 months ago

Agree and don't see any reason to use Enumerable... pls someone who votes for other than Queryable try to explain..

upvoted 2 times

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zimzimzimma

4 years, 9 months ago

I think it's A too. See here for an IQueryable vs IEnumerable explanation: https://www.codeproject.com/articles/732425/ienumerable-vs-iqueryable#:~:text=While%20querying%20data%20from%20database,server%20side%20with%20all%20filters.

upvoted 1 times

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SephGrave

Highly Voted 5 years, 5 months ago

Option D

upvoted 10 times

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not2smart

Most Recent 4 years, 10 months ago

The code for LoadHistorical() is missing from the question. This can be found on other web sites. The source of the historical data is XML related. private IEnumerable<HistoricalFlightInfo> LoadHistorical() { return HistoricalDataLoader.LoadHistoricalFlights(); } - I think the answer is D as the join will need to take place client-side between two IEnumerable objects. - Answer A using AsQueryable does not make sense, since the join cannot take place on the server-side and the whole purpose of using AsQueryable is to let the query run server-side for performance. And that will not work.

upvoted 7 times

Dreamchaser1980

4 years, 8 months ago

I validated the answer D on my computer, query is done server side, filtering is done client side.

upvoted 2 times

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Natali

5 years ago

D is right because you send result as REST so if you use “AsQueryable” the result is deferred to the next enumeration of your result. D is not optimized but will works. A will break at runtime. Credits to Rem

upvoted 7 times

mr_

4 years, 10 months ago

I'm not sure if I understood you but .AsEnumerable() will not cause to execute query on the DB imidietely if that is what you meant. In terms of being deferred both methods will work the same here. Method .AsEnumerable() is completly different from .ToList() in that matter.

upvoted 4 times

Jobair

4 years, 8 months ago

According to the following link .AsEnumerable() will load everything in the memory https://stackoverflow.com/questions/3311244/understanding-asenumerable-in-linq-to-sql

upvoted 1 times

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Tested38

5 years, 2 months ago

A, C are probably wrong because joins are not supported for azure tables https://docs.microsoft.com/en-us/rest/api/storageservices/query-operators-supported-for-the-table-service

upvoted 1 times

Gorilla

5 years ago

From the question: "The consolidated flight information is stored in a SQL Server database". Nothing about Azure Tables.

upvoted 4 times

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mmk1991

5 years, 3 months ago

Option C seems to enumerate historical twice (in each Where clause) which is IEnumerable, so it seems that option A would be the best in terms of performance.

upvoted 2 times

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