Explicit loading for list of entries: context.Entries(...)...Load()

For explicit loading EF Core offers (from docs):

var blog = context.Blogs
        .Single(b => b.BlogId == 1);

context.Entry(blog)
        .Reference(b => b.Owner)
        .Load();

If I have, for expample, list of 10 entries, I need to 10 times call Reference(…).Load() in foreach, that generate 10 SQL queries to DB.

How about optimized method Entries():

var blogs = context.Blogs
        .Where(...)
        .ToList();

context.Entries(blogs)
        .Reference(b => b.Owner)
        .Load();

which make a single SQL query like: select .... where [BlogOwner].[BlogId] in (?, ?, ?, ?, ?, ?)

Sorry, but I have not found similar functionality. Thanks

[Remleo]

Sometimes may need to eager/explicit load a relationship after the parent model has already been retrieved. For example, this may be useful if I need to dynamically decide whether to load related models:

// This code is responsible for retrieve specific blog entities
// But it has no idea about inner logic in BlackBox.SomeMethod()
// That is why it dont load Navigations
var neededBlogs = context.Blogs.Where(....).ToList();
....
if (someDynamicCondition)
        BlackBox.SomeMethod(context, neededBlogs);

....

public class BlackBox {
        public static void SomeMethod(DbContext context, IEnumerable<Blog> blogs)
        {
            // There might be code that ensure Owner loading, 
            // because this method has no idea about is `blogs` was preloaded `Owners` or not.
            // Also `Loader` should be intelligent enough for load only empty Navigations
            // so calling this method multiple times is safe
            context.Entries(blogs).Reference(b => b.Owner).Load(); // dry code... my vision :)

            foreach (var blog in blogs)
            {
                if (!string.IsNullOrEmpty(blog.Owner.email) && someDynamicCondition)
                {
                    SendNotificationToOwner(blog.Owner.email, "Alert!");
                }
            }
        }
}

This code works:

var ids = context.ChangeTracker
    .Entries<Blog>()
    .Select(e => e.Property(b => b.BlogId))
    .ToList();
context.Owner.Where(o => ids.Contains(o.BlogId)).Load();

but code is not “dry”. where statement need to be hardcoded and match FK for Navigation-property. Context knows all about FK so it’s his “job” to load Navigation-properties properly.

Sorry for my english (

[divega]

To things you can try:

• Use eager loading, i.e. Include(b => b.Owner)
• Write a query like this (I haven’t actually tested it, but it should work):

var ids = context.ChangeTracker
    .Entries<Blog>()
    .Select(e => e.Entity.BlogId)
    .ToList();
context.Owner.Where(o => ids.Contains(o.BlogId)).Load();