Add project files.

DiaryApp/Models/DiaryEntry.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace DiaryApp.Models
+{
+    public class DiaryEntry
+    {
+        //[Key]
+        public int Id { get; set; }
+        [Required(ErrorMessage = "Please enter a title")]
+        [StringLength(50, MinimumLength = 3,
+            ErrorMessage = "Title must be between 3 and 100 Characters!")]
+        public string Title { get; set; } = string.Empty;
+        [Required]
+        public string Content { get; set; } = string.Empty;
+        [Required]
+        public DateTime DateCreated { get; set; } = DateTime.Now;
+    }
+}

DiaryApp/Models/ErrorViewModel.cs

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+namespace DiaryApp.Models
+{
+    public class ErrorViewModel
+    {
+        public string? RequestId { get; set; }
+
+        public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
+    }
+}