Lazy loading properties after an insert

Question

I have a parent and child object. If I do the following

Child c = new Child();

c.ParentID = parentID;
context.Child.Add(c);
context.SaveChanges();

int i = c.Parent.ParentID; // throws an exception b/c Parent is null

Why is this doing this? If I get a new context (after saving), I can see Parent just fine.

possible duplicate of Entity Framework: I set the foreign key, SaveChanges then access the navigation property, but it doesn't load the related entity. Why not? — Iain Galloway
– Iain Galloway, Commented May 7, 2014 at 12:45
WHat will you do if context.Child is null ? I am getting null in my case, Any sugessions ? — Ashish-BeJovial
– Ashish-BeJovial, Commented May 31, 2016 at 10:48

Slauma · Accepted Answer · 2011-06-11 00:25:23Z

11

I guess you are working with lazy loading enabled. If you want that the navigation property gets populated after adding the object with the foreign key property to the context you must use the Create method of DbSet (instead of instantiating the object with new):

Child c = context.Child.Create();

With active lazy loading this will create a proxy object which ensures that the navigation property gets loaded.

answered Jun 11, 2011 at 0:25

Slauma

177k60 gold badges407 silver badges424 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

AdamH Over a year ago

This explained why I couldn't navigate into any parent navigational properties when everything else I was reading suggested it should just work. Thanks.

Jordan Over a year ago

@Slauma This is great, thank you. But how do I use the Create() method if my Child object has a constructor with required values? e.g. normally I would do Child c = new Child(OtherObject o). Obviously context.Child.Create(o) doesn't work.

Slauma Over a year ago

@Jordan: It's not possible. Create can only instantiate an entity via a default constructor. You must set entity properties after calling Create (or call something like an Init method which you pass the parameters into).

LeonardoX · Accepted Answer · 2020-11-12 02:14:55Z

A bit late after the question but just to clarify. As MS docs states here, I use this instead:

using (var context = new BloggingContext())
{
    var post = context.Posts.Find(2);

    // Load the blog related to a given post.
    context.Entry(post).Reference(p => p.Blog).Load();

    // Load the blog related to a given post using a string.
    context.Entry(post).Reference("Blog").Load();

    var blog = context.Blogs.Find(1);

    // Load the posts related to a given blog.
    context.Entry(blog).Collection(p => p.Posts).Load();

    // Load the posts related to a given blog
    // using a string to specify the relationship.
    context.Entry(blog).Collection("Posts").Load();
}

But it will work only if you use the Add() method

context.Set<T>().Add(post);
context.SaveChanges();
context.Entry(post).Reference(p => p.Blog).Load();

it will not work with .AddRange()

Collectives™ on Stack Overflow

Lazy loading properties after an insert

2 Answers 2

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related