Refactor. Add data layer

BudgetApp.Data/Entities/Transaction.cs

@@ -0,0 +1,35 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace BudgetApp.Data.Entities;
+
+public class Transaction
+{
+    public int Id { get; set; }
+
+    [Required, MaxLength(200)]
+    public string Description { get; set; } = string.Empty;
+
+    public decimal Amount { get; set; }
+
+    public DateTime Date { get; set; } = DateTime.Today;
+
+    public TransactionType Type { get; set; } = TransactionType.Expense;
+
+    public RecurrenceType RecurrenceType { get; set; } = RecurrenceType.None;
+
+    public DateTime? RecurrenceEndDate { get; set; }
+
+    public int? ParentTransactionId { get; set; }
+    public Transaction? ParentTransaction { get; set; }
+
+    public int AccountId { get; set; }
+    public Account Account { get; set; } = default!;
+
+    public int? CategoryId { get; set; }
+    public Category? Category { get; set; }
+
+    public bool IsPaid { get; set; } = false;
+
+    public int? SalaryId { get; set; }
+    public Salary? Salary { get; set; }
+}