Entity not loading properly in code first approrach

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Student
Id
Name

Subject
Id
Name


StudentSubject

[ForeignKey("StudentId")]
        public virtual Student Student { get; set; }
        public Guid StudentId { get; set; }

        [ForeignKey("SubjectId")]
        public virtual Subject Subject { get; set; }
        public  Guid SubjectId { get; set; }

        public decimal ChargeRate { get; set; }

when i start application firstly.Then all entities loaded properly.
when i delete some record then i check some entities not loaded properly.
Ex:
when i get student's subject like
std.StudentSubjects,then it give me information about subject null.

plz help me its urgent.