DataAnnotations – ForeignKey Attribute


ForeignKey attribute can be applied to properties of a class. Default Code-First convention for ForeignKey relationship expects foreign key property name match with primary key property.

Consider the following example.

public class Student
{
    public Student()
    { 
        
    }
    public int StudentID { get; set; }
    public string StudentName { get; set; }
        
    //Foreign key for Standard
    public int StandardId { get; set; }

    public Standard Standard { get; set; }
}

public class Standard
{
    public Standard()
    { 
        
    }
    public int StandardId { get; set; }
    public string StandardName { get; set; }
    
    public ICollection<Student> Students { get; set; }
   
    }

As you can see in the above code, Student class includes foreign key StandardId, which is key property in Standard class. So now, Code First will create StandardId column in Students class as shown below.

Entity Framework code-first example

ForeignKey attribute overrides this convention. You can have a different name of a foreign key property name than the primary key of a dependent class.

public class Student
{
    public Student()
    { 
        
    }
    public int StudentID { get; set; }
    public string StudentName { get; set; }
        
    //Foreign key for Standard
    public int StandardRefId { get; set; }

    [ForeignKey("StandardRefId")]
    public Standard Standard { get; set; }
}

public class Standard
{
    public Standard()
    { 
        
    }
    public int StandardId { get; set; }
    public string StandardName { get; set; }
    
    public ICollection<Student> Students { get; set; }
   
}

As you can see in the above example, Student class includes StandardRefId foreign key property name instead of StandardId. We specify it using ForeignKey attribute on Standard navigation property so that Code-First will consider StandardRefId as foreign key, as shown below.

Entity Framework code-first example

ForeignKey attribute can be applied to key property to specify which navigation property it points to, as shown below.

public class Student
{
    public Student()
    { 
        
    }
    public int StudentID { get; set; }
    public string StudentName { get; set; }
        
    //Foreign key for Standard
    
    [ForeignKey("Standard")]
    public int StandardRefId { get; set; }

    public Standard Standard { get; set; }
}

public class Standard
{
    public Standard()
    { 
        
    }
    public int StandardId { get; set; }
    public string StandardName { get; set; }
    
    public ICollection<Student> Students { get; set; }
   
}

Thus, you can use ForeignKey attribute to give a different name to a foreign key property.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s