Why do I need a foreign key in a class in the Entity Framework?

Question

Let's say I have 2 classes: Ninjahas-many NinjaEquipment. Inside NinjaEquipmentme there: public Ninja Ninja { get; set; }. I saw that some people also include, for example, foreign key references: public int NinjaID { get; set; }. What is the point of doing this? Isn't this a simple link Ninjaif I want to switch to a parent-to-one-to-many relationship?

Answer 1

What is the meaning of this?

I believe this is the difference between foreign keys and navigation properties.

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Answer 2

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:

public class NinjaEquipmentMap : EntityTypeConfiguration<NinjaEquipment>
{
    public NinjaEquipmentMap
    {
        // Fluent API examples:

        // Describes the relationship between the entities 
        // and the property to use as the foreign key.
        this.HasRequired(t => t.Ninja)
            .WithMany(c => c.NinjaEquipment)
            .HasForeignKey(c => c.NinjaId);

        // I can specify a relationship using a property name
        // that existed in my existing database.
        this.HasRequired(t => t.Ninja)
            .WithMany(c => c.NinjaEquipment)
            .HasForeignKey(c => c.SuperNinjaId);
    }
}

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// 
// BEFORE
// 
var ninjaEquipment = dbContext.Set<NinjaEquipment>().Find(1);

// We have to load the Ninja record to find out the related Ninja ID
var ninjaId = ninjaEquipment.Ninja.Id;

// 
// AFTER
// 
var ninjaEquipment = dbContext.Set<NinjaEquipment>().Find(1);

// Find out the Ninja equipment ID without having to load the Ninja
var ninjaId = ninjaEquipment.NinjaId;

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Answer 3

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Answer 4

, / : , NinjaID NinjaEquipment, ( ) Ninja.

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