EF: Loading related objects of related objects

Question

I can´t find a way to load an object from a DB with all its related objects. Concerning this simplified model (ID-Properties not shown):

class MainClass 
{  
    public virtual ICollection<FirstLevelClass> FirstLevelObjects {get; set;}  
}

class FirstLevelClass
{  
    public virtual ICollection<SecondLevelClassA> SecondLevelObjectsA {get; set;}
    public virtual ICollection<SecondLevelClassB> SecondLevelObjectsB {get; set;}
}

class SecondLevelClassA
{
    public virtual int SomeValue {get; set;}

}
class SecondLevelClassB
{
    public virtual int SomeValue {get; set;}

}

The DbContext is on "MainClass"-Objects:

public SampleContext : DbContext
{
    public DbSet<MainClass> MainClassObjects {get; set;}
}

How can I load an MainClass-object from db with all first- and second-level-objects? I can do:

using (var context = new SampleContext())
{
    var MainClassObjects = context.MainClassObjects.Include(p => p.FirstLevelObjects).ToList();

    // ...move objects from the context to program logic...

}

but how do I get SecondLevelObjects? I´m missing something like:

using (var context = new SampleContext())
{
    var MainClassObjects = context.MainClassObjects.Include(p => p.FirstLevelObjects.SecondLevelObjects).ToList();

    // ...move objects from the context to program logic...

}

Is this even possible or do I have to adapt the DbSets in the DbContext?

VahidNaderi · Accepted Answer · 2014-01-17 11:24:07Z

2

One solution can be to use Include method's other overload which takes a string like this:

var MainClassObjects = context.MainClassObjects
.Include("FirstLevelObjects")
.Include("FirstLevelObjects.SecondLevelObjects")
.ToList();

Update:

When you're using this method you just need to determine the paths you want to fetch so for updated question you can use this:

var MainClassObjects = context.MainClassObjects
.Include("FirstLevelObjects.SecondLevelObjectsA")
.Include("FirstLevelObjects.SecondLevelObjectsB")
.ToList();

edited Jan 17, 2014 at 11:24

answered Jan 17, 2014 at 10:37

VahidNaderi

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4 Comments

ElDog Over a year ago

In fact, if you use line Include("FirstLevelObjects.SecondLevelObjects") you don't even need to use Include("FirstLevelObjects")

tafkab76 Over a year ago

I even tried that before, but it didn´t work at all. I couldn´t even include FirstLevelObjects only. Maybe I was missing something, I will try again.

tafkab76 Over a year ago

It works now, I have no idea what I was missing before. Thanks! But also using this way, I´m nit quite sure how to include two List-Properties of one object. (See updated question).

tafkab76 Over a year ago

Your edited answer (with two different SecondLevelObjects) works perfectly, thanks again!

Loetn · Accepted Answer · 2014-01-17 12:06:22Z

1

Try this:

using (var context = new SampleContext())
{
    var MainClassObjects = context.MainClassObjects.Include(p => p.FirstLevelObjects.SelectMany(s => s.SecondLevelObjects)).ToList();

// ...move objects from the context to program logic...

}

You should add a .Select() statement to get an object or a list.

edited Jan 17, 2014 at 12:06

answered Jan 17, 2014 at 10:33

Loetn

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2 Comments

tafkab76 Over a year ago

this works so far, thanks! .SelectMany() gives an ArgumentException although SecondLevelObjects is a list. .Select does the job. but now I´m facing another problem: how do I include two "List-Properties" in one class? (Question above updated)

Loetn Over a year ago

My bad, it also should be .Select() for a list. Answer updated.

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