Include 内部使用的 Lambda 表达式无效。 EF6，导航属性

Question

I was trying to solve a many to many relation. On a database level everthing looks good to me, but when I tryr to get that data( inlcude ), it fails.

I get:

Lambda expression used inside Include is not valid.

What I call/tried:

var readRecipes = db.MyClasses. 
                     Include(blog => blog.SomeCollections).ThenInclude(post => post.Prop1).
                     Include(blog => blog.SomeCollections).ThenInclude(post => post.Prop2).

Structure

MainClass:

public class MainClass{
// ...                   
public ICollection<NavigationProperty> NavigationPropertys; 
// ...               
public MainClass()
{

    this.NavigationPropertys = new Collection<NavigationProperty>(); 
}
}

NavigationProperty:

public class NavigationProperty
    {
        public Guid ID { get; set; }



        [Required]
        public Guid? Prop1ID { get; set; }// 0,*

        [Required]
        public Guid? Prop2ID { get; set; }// 0,*

        [Required]
        public Guid MainClassID { get; set; }



        [Required]
        public Prop1 Prop1 { get; set; }

        [Required]
        public Prop2 Prop2 { get; set; }




        public MainClass MainClass { get; set; }



        [Required]
        public float Amount { get; set; }


        public NavigationProperty()
        {
            // todo: ?
        }
    }

I don't know, what I did wrong?

Answer 1

Ok, I solved my question.

Instead of:

public ICollection<NavigationProperty> NavigationPropertys; 

I should have used:

public ICollection<NavigationProperty> NavigationPropertys { get; set; }; 

This made Lambda crash.

Thank You.

Answer 2

If you want to include the children of a navigational property as well you should do:

Parent.Include(p => p.Children.Select(c => c.GrandChild));

or if there are many grand children per child

Parent.Include(p => p.Children.SelectMany(c => c.GrandChildren));

or if there is only one child and one grand child per parent.

Parent.Include(p => p.Child.GrandChild);

I hope this helps.

EDIT: I didn't realise that your question was regarding ef-core. I thought it was some type of pseudo code or self made extension method.

Have you read through all the examples provided by Microsoft regarding this topic? Otherwise I'm afraid that I don't have enough info to assist you in the matter.

One thing that I'll need to see is how you configured the relationship between Prop1 and the Navigation entity. I don't see a foreign key in your model. Of course this is not necessary depending on how you configured the relationship in the overridden OnModelCreating method using the modelBuilder in your DbContext or how you used the attributes to indicate the relationship. More about relationships and specifying relationships in ef-core can be foundhere .