重构项目结构，移除Assignment相关功能，优化Submission模块

Entities/Contracts/Textbook/KeyPoint.cs

@@ -18,14 +18,14 @@ namespace Entities.Contracts
 		public string Key { get; set; } = string.Empty;
 
 		
+
 		[Required]
 		public Guid LessonID { get; set; }
-
 		[ForeignKey(nameof(LessonID))]
-		public Lesson Lesson { get; set; }
+		public virtual Lesson Lesson { get; set; }
 
 
-		public ICollection<Question> Questions { get; set; }
+		public virtual ICollection<Question> Questions { get; set; }
 
 		public KeyPoint()
 		{

Entities/Contracts/Textbook/Lesson.cs

@@ -21,19 +21,19 @@ namespace Entities.Contracts
 
 		[Required]
 		public Guid TextbookID { get; set; }
-
-
 		[ForeignKey(nameof(TextbookID))]
-		public Textbook Textbook { get; set; }
+		public virtual Textbook Textbook { get; set; }
+
+
 
 		[InverseProperty(nameof(KeyPoint.Lesson))]
-		public ICollection<KeyPoint>? KeyPoints { get; set; }
+		public virtual ICollection<KeyPoint>? KeyPoints { get; set; }
 
 		[InverseProperty(nameof(Question.Lesson))]
-		public ICollection<Question>? Questions { get; set; }
+		public virtual ICollection<Question>? Questions { get; set; }
 
 		[InverseProperty(nameof(LessonQuestion.Lesson))]
-		public ICollection<LessonQuestion>? LessonQuestions { get; set; } 
+		public virtual ICollection<LessonQuestion>? LessonQuestions { get; set; } 
 
 
 

Entities/Contracts/Textbook/LessonQuestion.cs

@@ -19,9 +19,9 @@ namespace Entities.Contracts
 
 		[Required]
 		public Guid LessonID { get; set; }
-
 		[ForeignKey(nameof(LessonID))]	
-		public Lesson Lesson { get; set; }
+		public virtual Lesson Lesson { get; set; }
+
 
 		public LessonQuestion()
 		{

Entities/Contracts/Textbook/Textbook.cs

@@ -24,7 +24,7 @@ namespace Entities.Contracts
 		public SubjectAreaEnum SubjectArea { get; set; } = SubjectAreaEnum.Unknown;
 
 		[InverseProperty(nameof(Lesson.Textbook))]
-		public ICollection<Lesson> Lessons { get; set; }
+		public virtual ICollection<Lesson> Lessons { get; set; }
 
 		public Textbook()
 		{