C#•2w ago

✅ How does explicit loading differs from lazy loading when using EF Core

Hello guys, I was reading about the methods used to load data in EF Core. I came across eager loading, explicit loading and lazy loading. I understood that eager loading is loading data directly with the query, while lazy loading is loading the data as we go, like in a for-each loop. But I didn't understand the explicit loading can someone explain please. If explicit loading is loading data when we need, isn't it the same thing as lazy loading?

24 Replies

Angius•2w ago

Never heard of explicit loading, at least not in the context of eager/lazy Only thing that comes to mind would be maybe .Select()ing into a DTO, to explicitly choose which columns to load?

jcotton42•2w ago

@Faker Explicit loading must be done, well, explicitly. Lazy is implicit, and always sync.

jcotton42•2w ago

@Angius https://learn.microsoft.com/en-us/ef/core/querying/related-data/explicit

Explicit Loading of Related Data - EF Core

Explicit loading of related data with Entity Framework Core

Angius•2w ago

Huh So it's basically "I really want to use lazy loading, but I really don't want to use lazy loading"

jcotton42•2w ago

"I need to load conditionally after the fact," I guess.

FakerOP•2w ago

hmm is there any use case of explicit loading?

jcotton42•2w ago

Eager: you do things right. Explicit: weird edge case. Lazy: you hate your users.

Angius•2w ago

Basically lol Tbh I can't really see the much use for explicit loading, so it's hard for me to say what example usage would be

FakerOP•2w ago

yep, will just stick with eager / lazy loading for now but at least I know it exist :kekw:

Angius•2w ago

Maybe something like

var post = await _ctx.Posts.FirstOrDefaultAsync(p => p.Id == id);
if (data.NewTags is { Length: > 0 })
{
    await _ctx.Entry(post)
        .Collection(p => p.Tags)
        .LoadAsync();
}

var post = await _ctx.Posts.FirstOrDefaultAsync(p => p.Id == id);
if (data.NewTags is { Length: > 0 })
{
    await _ctx.Entry(post)
        .Collection(p => p.Tags)
        .LoadAsync();
}

so that you load the tags only when there are actual tags to edit?

jcotton42•2w ago

@Faker don't use lazy. is bad

FakerOP•2w ago

ahh I see

Angius•2w ago

Why lazy loading is bad:

foreach (var tag in post.Tags)
{
    <div class="tag">@tag.Name</div>
}

foreach (var tag in post.Tags)
{
    <div class="tag">@tag.Name</div>
}

Assuming Post has a lazy nav property to Tags, each loop here is a separate, synchronous, database query

FakerOP•2w ago

I don't really use it in a foreach loop, like I do this:

C#
var instructors = context.Instructors.AsNoTracking().ToList();
                foreach (var instructor in instructors)
                {
                    Console.WriteLine(instructor);
                }

C#
var instructors = context.Instructors.AsNoTracking().ToList();
                foreach (var instructor in instructors)
                {
                    Console.WriteLine(instructor);
                }

like the foreach is lazy loading, but for eager loading, I think I need to use Include() in the fluent api ?

Angius•2w ago

Or better yet, .Select()

FakerOP•2w ago

yeah I see, we would have one roundtrip for each tags?

Angius•2w ago

Yeah, if you can load the post and the tags in a single query Or better yet, the post, and the tag names since you're not using other tag properties

jcotton42•2w ago

@Faker that's not lazy loading.

Angius•2w ago

Hence select

FakerOP•2w ago

oh Select also loads data eagerly, that why we can kind of project things ?

Angius•2w ago

ye .Include(), .ThenInclude() loads everything eagerly, .Select() loads only the selected columns eagerly

FakerOP•2w ago

yeah sorry, the example that @Angius gave was more appropriate

Angius•2w ago

SELECT * FROM tbl vs SELECT t.Name, t.Skunga FROM tbl t

FakerOP•2w ago

AHHHH I see yeah It's clearer now, thanks guys 👍

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✅ How does explicit loading differs from lazy loading when using EF Core

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