added new Methodes to KatalogModel

Models/KatalogModel.cs

@@ -76,12 +76,24 @@ namespace BuecherwurmAPI.Models
         }
         public void DeleteBook(Book book)
         {
-
+            using (var command = _dbConnection.CreateCommand())
+            {
+                // funktioniert das so?
+                command.Parameters.Add(new SqliteParameter("@id", SqliteType.Integer)).Value = book.ProductId;
+                command.CommandText = @"DELETE * FROM Books WHERE ProductId= @id";
+                var dataReader = command.ExecuteReader();
+            }
         }
 
         public void AddBook (Book book)
         {
-
+            using (var command = _dbConnection.CreateCommand())
+            {
+                // funktioniert das so?
+                command.Parameters.Add(new SqliteParameter("@id", SqliteType.Integer)).Value = book.ProductId;
+                command.CommandText = @"INSERT INTO Books (Name, Author, Country, Link, Language, Pages, Year, ProductId, Category, ImageLink, LendTime, LendType) ";
+                var dataReader = command.ExecuteReader();
+            }
         }
 
         public void EditBook (Book book)

Models/Lend.cs

@@ -1,9 +1,12 @@
 using System;
+using System.ComponentModel.DataAnnotations;
 
 namespace BuecherwurmAPI.Models
 {
     public class Lend
     {
+        [Key]
+        [Required]
         public long Id { get; set; }
         public long ItemId { get; set;}
         public DateTime ReturnDate { get; set; }