Set a property to a non-null value of type 'System.Double'

Question

How do I resolve this error?

The 'CreditsEarned' property on 'Student' could not be set to a 'null' value. You must set this property to a non-null value of type 'System.Double'.

Here is my code:

public class Student : Person
{
    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    [Display(Name = "Enrollment Date")]
    public DateTime EnrollmentDate { get; set; }

    // Credits earned
    [Display(Name = "Credits Earned")]
    public double CreditsEarned { get; set; }

    // GPA
    [Display(Name = "GPA")]
    [Range(typeof(double), "0.7", "4.0")]
    public double Gpa { get; set; }


    public virtual ICollection<Enrollment> Enrollments { get; set; }
}

Answer 1

May I ask you why do you want to set an double type to null ?

The double type in C# is not null by default. You must explicitly set it to null.

[Display(Name = "Credits Earned")]
public double? CreditsEarned { get; set; }

Notice the question mark after the declaration of the type. In C# this tells the compiler that that type might be flagged at nullable.

EDIT:

Please see following links:

1) Nullable Types in C#

2) Nullable Types in C# examples

Answer 2

Using Double? (a ullable of type Double) instead, to allow the property to hold null-values has already been mentioned.

Another option may be to initialize the property to 0, and make sure it is always 0 or some other number.

public class Student : Person
{
    // This will make sure the value is initially defined (to 0):
    public Student(){
        CreditsEarned = 0;
    }

    ...

    // Credits earned
    [Display(Name = "Credits Earned")]
    public double CreditsEarned { get; set; }

Answer 3

you should try

// Credits earned
[Display(Name = "Credits Earned")]
public double? CreditsEarned { get; set; }