problem entity revises

Author: jackzhenguo

Entity/Problem.cs

@@ -12,10 +12,12 @@ public class Problem
         public int ProblemId { get; set; }
         [MaxLength(50)]
         [Required(ErrorMessage = "Title is required.")]
+        public string Number { get; set; }
         public string Title { get; set; }
         public string LtUrl { get; set; }
         public string CsdnAddress { get; set; }
         public string Content { get; set; }
-        public virtual IList<Tag> Tags { get; set; }
+        public string TagsCombine { get; set; }//it's separated by ';'
+        public virtual IList<Tag> Tags { get; set; } //it's a navigation property
     }
 }