Entity framework lazy loading after id update

Question

I have a Person and Occupation table in my DB. When I create a Person, their default OccupationId is null.

Let's say that I created a person and their Id is 11. Also, there is an occupation, let's say Diver, and its Id is 53. I then do the following:

using (var context = new DbEntities())
{
    person.OccupationId;  //currently null
    person.Occupation;    //currently null

    var person = context.People.First(x => x.Id == 11);
    person.OccupationId=53;
    context.SaveChanges();

    var occupation = person.Occupation.Description;  //Exception: Occupation is null
}

The code fails on the last line because the occupation was initially null and the new occupation didn't get lazy loaded after the save. If the person had an occupation before running this code and the old Occupation was lazy loaded, then the new Occupation would come up after the save.

In other words, if the person had an Occupation of Janitor first then this would work:

using (var context = new DbEntities())
{
    var person = context.People.First(x => x.Id == 11);

    var occupation = person.Occupation.Description; //this would say Janitor

    person.OccupationId=53;
    context.SaveChanges();

    var occupation = person.Occupation.Description;  //This would say Diver
}

Is there a way to lazy load the new Occupation after the save if the initial Occupation was null?

Metalstorm · Accepted Answer · 2012-06-28 07:22:23Z

1

I'm not entirely clear on the question, but here's shot:

public class People
{
    private Occupation occupation = null;
    public Occupation Occupation
    {
        get { return this.GetOccupation(); }
        set { this.occupation = value; }
    }

    private Occupation GetOccupation()
    {
        return this.GetOccupation(false);
    }

    private Occupation GetOccupation(bool force)
    {
        if(this.occupation == null || force)
        {
            using (var context = new DbEntities())
            {
                this.occupation = context.Occupation.First(x => x.Id == this.OccupationId);
            }
        }
        return this.occupation;
    }
}

Here's a simple example of lazy-loading with the ability to do a force reload.

In the SaveChanges() you can just call this.Occupation = null; The next time someone accesses it, it will lazy load it. Or, you could call this.GetOccupation(true); which will force reload the Occupation, but then that's kinda defeating the purpose of lazy-loading. (IE. only loading something when it's needed)

answered Jun 28, 2012 at 7:22

Metalstorm

3,3703 gold badges30 silver badges24 bronze badges

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

3 Comments

Metalstorm Over a year ago

Looking at your edits, it shouldn't matter if 'Occupation' is null, as it will get lazy loaded... that's the whole point of lazy loading.

VARAK Over a year ago

Thanks for your answer. I guess this would work but I wanted something less "Hacky" :) I ended up using this: if(person.Occupation==null && person.OccupationId!=null) context.Entry(person).Reference(x=>x.Occupation).Load();

Metalstorm Over a year ago

I wouldn't say the implementation I posted was 'hacky' it's good OO as far as i'm aware.

VARAK · Accepted Answer · 2012-06-28 07:50:37Z

0

I ended up using this:

if(person.Occupation==null && person.OccupationId!=null)
     context.Entry(person).Reference(x=>x.Occupation).Load();

I'm sure that there is a way to make the Occupation load automatically once saved but I've had no luck with my attempts as yet.

answered Jun 28, 2012 at 7:50

VARAK

84510 silver badges29 bronze badges

Collectives™ on Stack Overflow

Entity framework lazy loading after id update

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related