CODEWITHSUNDEEP
entity-framework
Manish
Manish

Reputation: 1776

Why does EntityFramework return entire objects when I only ask for one column?

I am investigating slow performance over the network of my application which uses EntityFramework version 5. One option I tried was to retrieve only the Id field, instead of the entire object. However, examining in Wireshark, I see that all objects are transferred anyway. In other words, the following two code blocks cause exactly the same network activity. Would anyone know how I can cause the db to only return Ids in the first query?

List<long> test = dbContext.UserActivities
          .Where(ua => ua.Activity.Id == activityId)
          .Select(ua => ua.User)
          .ToList()
          .Select(u => u.Id)
          .ToList();

List<long> test = dbContext.UserActivities
          .Where(ua => ua.Activity.Id == activityId)
          .Select(ua => ua.User)
          .ToList();

Upvotes: 1

Views: 66

Answers (2)

Lotok
Lotok

Reputation: 4607

.ToList() materializes the object. Essentially, executing the query. Anything after is LINQ to Objects.

try something like this: 

List<long> test = dbContext.UserActivities
          .Where(ua => ua.Activity.Id == activityId)
          .Select(ua => ua.User.Id).ToList();

Upvotes: 4

Aducci
Aducci

Reputation: 26654

List<long> test = dbContext.UserActivities
          .Where(ua => ua.Activity.Id == activityId)
          .Select(ua => ua.User.Id).ToList();

Upvotes: 2

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