DataAnnotations - NotMapped Attribute:

NotMapped attribute can be applied to properties of a class. Default Code-First convention creates a column for all the properties which includes getters and setters. NotMapped attribute overrides this default convention. You can apply NotMapped attribute to a property which you do NOT want to create a column in a database table for.

Consider the following example.

using System.ComponentModel.DataAnnotations;

public class Student
{
    public Student()
    { 
        
    }

    public int StudentId { get; set; }
     
    public string StudentName { get; set; }
        
    [NotMapped]
    public int Age { get; set; }
}

As you can see in the above example, NotMapped attribute is applied to Age property of the Student class. So, Code First will not create a column to store Age information in the Student table as shown below.

Code-first also does not create a column for a property which does not have either getters or setters. Code-First will not create columns for FirstName and Age properties in the following example.

using System.ComponentModel.DataAnnotations;

public class Student
{
    public Student()
    { 
        
    }
    private int _age = 0;

    public int StudentId { get; set; }
     
    public string StudentName { get; set; }
    
    public string FirstName { get{ return StudentName;}  }
    public string Age { set{ _age = value;}  }
    
}

Entity Framework Code-First（9.10）：DataAnnotations - NotMapped Attribute

原文：http://www.cnblogs.com/purplefox2008/p/5644209.html