C
C#•3y ago
Thinker

Turn recursive entities into model [Answered]

I have two db entities like this: 
public sealed class TodoListEntity {
  public Guid Id { get; set; }
  public ICollection<TodoItemEntity> Items { get; set; } = null!;
}
public sealed class TodoListEntity {
  public Guid Id { get; set; }
  public ICollection<TodoItemEntity> Items { get; set; } = null!;
}
public sealed class TodoItemEntity {
  public Guid Id { get; set; }
  // Other data

  public Guid ListId { get; set; }
  public TodoListEntity List { get; set; } = null!;
}
public sealed class TodoItemEntity {
  public Guid Id { get; set; }
  // Other data

  public Guid ListId { get; set; }
  public TodoListEntity List { get; set; } = null!;
}
I wanna turn this into a model/DTO, so I have these extensions 
public static TodoList ToModel(this TodoListEntity entity) =>
  new(entity.Id, entity.Items.Select(ToModel).ToArray());
public static TodoItem ToModel(this TodoItemEntity entity) =>
  new(entity.Id, /* Other data */, entity.List.ToModel());
public static TodoList ToModel(this TodoListEntity entity) =>
  new(entity.Id, entity.Items.Select(ToModel).ToArray());
public static TodoItem ToModel(this TodoItemEntity entity) =>
  new(entity.Id, /* Other data */, entity.List.ToModel());
This however causes a stack overflow because ToModel(TodoListEntity) calls ToModel(TodoItemEntity) and so on which causes unbound recursion. What would the simplest way to fix this be? I somehow have to keep a single list which I can pass to all items inside it.
2 Replies
Thinker
ThinkerOP•3y ago
And I know it's not "recursive" entities but it's entities with backrefs Okay nvm I think I figured it out using this 
public static TodoList ToModel(this TodoListEntity entity) {
  List<TodoItem> items = new();
  TodoList list = new(entity.Id, items);

  foreach (var item in entity.Items) {
    items.Add(ToModelShallow(item, list));
  }

  return list;
}
private static TodoItem ToModelShallow(TodoItemEntity entity, TodoList list) =>
  new(entity.Id, /* Other data */, list);
public static TodoItem ToModel(this TodoItemEntity entity) =>
  entity.List.ToModel().Items.First(e => e.Id == entity.Id);
public static TodoList ToModel(this TodoListEntity entity) {
  List<TodoItem> items = new();
  TodoList list = new(entity.Id, items);

  foreach (var item in entity.Items) {
    items.Add(ToModelShallow(item, list));
  }

  return list;
}
private static TodoItem ToModelShallow(TodoItemEntity entity, TodoList list) =>
  new(entity.Id, /* Other data */, list);
public static TodoItem ToModel(this TodoItemEntity entity) =>
  entity.List.ToModel().Items.First(e => e.Id == entity.Id);
Accord
Accord•3y ago
✅ This post has been marked as answered!

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