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Explicit Loading of Related Data

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  • قراءة خلال 2 دقائق

Explicit loading

You can explicitly load a navigation property via the DbContext.Entry(...) API.

using (var context = new BloggingContext())
{
    var blog = context.Blogs
        .Single(b => b.BlogId == 1);

    context.Entry(blog)
        .Collection(b => b.Posts)
        .Load();

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

You can also explicitly load a navigation property by executing a separate query that returns the related entities. If change tracking is enabled, then when query materializes an entity, EF Core will automatically set the navigation properties of the newly loaded entity to refer to any entities already loaded, and set the navigation properties of the already-loaded entities to refer to the newly loaded entity.

You can also get a LINQ query that represents the contents of a navigation property.

It allows you to apply other operators over the query. For example, applying an aggregate operator over the related entities without loading them into memory.

using (var context = new BloggingContext())
{
    var blog = context.Blogs
        .Single(b => b.BlogId == 1);

    var postCount = context.Entry(blog)
        .Collection(b => b.Posts)
        .Query()
        .Count();
}

You can also filter which related entities are loaded into memory.

using (var context = new BloggingContext())
{
    var blog = context.Blogs
        .Single(b => b.BlogId == 1);

    var goodPosts = context.Entry(blog)
        .Collection(b => b.Posts)
        .Query()
        .Where(p => p.Rating > 3)
        .ToList();
}