Entity Framework 的懒加载、预先加载、显示加载

1.新建两个实体，一个班级有多个学生

public class Student
{
    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public Grade Grade { get; set; }

}

public class Grade
{
    public int GradeId { get; set; }
    public string GradeName { get; set; }
    public string Section { get; set; }

    public virtual ICollection<Student> Students { get; set; }
}public class Student
{