Entity Framework Core : Access parent from child

Question

Might be a silly question but I'm a bit confused here.

I have a parent entity which contains a list of children.

public class Parent
{
    public int Id { get; set; }

    public List<Child> Children { get; set; }
}

public class Child
{
    public int Id { get; set; }
}

EFcore will create a ParentId as a foreign key in the table Child.

Now, let's say I want to retrieve all the children that have a specific Parent, how should I do it ? The ParentId is not available in the Child object.

Therefore, I cannot do something like:

var result = model.Child.Where(child => child.ParentId == 3);

I could add the ParentId property to the child in the entity, but I really don't want this property to be assigned manually. And if I set it as readonly by specifying the getter only, the migration doesn't work anymore.

Answer 1

EF Core allows you to access the associated shadow property in LINQ to Entities query using the EF.Property method:

Addresses a given property on an entity instance. This is useful when you want to reference a shadow state property in a LINQ query. Currently this method can only be used in LINQ queries and can not be used to access the value assigned to a property in other scenarios.

All you need to know is the name and the type - in your case they are "ParentId" and int? (optional):

var result = model.Child.Where(child => EF.Property<int?>(child, "ParentId") == 3);

Answer 2

I would recommend you have both the references (child-parent and parent-children) in the respective classes as provided in @ScotG answer.

However,since you dont want that, in EF using lazy loading you can do something like model.Parents.Find(3).Children since from the Parent class you have the references of its children.