Initial code changes to insert/update Ebook records

lib/Library.php

@@ -673,6 +673,24 @@ class Library{
 		}
 	}
 
+	public static function GetEbookByIdentifier(?string $identifier): ?Ebook{
+		if($identifier === null){
+			return null;
+		}
+
+		$result = Db::Query('
+				SELECT *
+				from Ebooks
+				where Identifier = ?
+			', [$identifier], 'Ebook');
+
+		if(sizeof($result) == 0){
+			return null;
+		}
+
+		return $result[0];
+	}
+
 	/**
 	 * @throws Exceptions\AppException
 	 */