LINQ Select Statement to Map Entity Using Recursion

Question

I have a Category Entity that has a collection of child Categories and a nullable reference to a Parent Category.

public class Category
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? ParentId { get; set; }

    public Category Parent { get; set; }
    public ICollection<Category> Children { get; set; } 
}

I have the scenario where I need to "copy" an existing entity (Zone) which has references to Categories. Within the select statement I need to map the existing categories and their children to a new Category record so that when I save the new categories will hold a reference to the new copied Zone.

The problem I'm having is a recursion method that will loop through the current LINQ select (x) Category and create new Category records for each of its children s children etc.

Here is the relevant part of the current "copy" select statement I have. Do I call Where on Categories that are top level i.e don't have a ParentId and then use a recursive method for the children?

Categories = zone.Categories.Where(y => !y.ParentId.HasValue).Select(x => new Category
{
     Children = WHAT DO I PUT IN HERE
     Name = x.Name,
}).ToList()

Seva · Accepted Answer · 2019-03-15 11:48:59Z

2

Are you perhaps looking for a copy constructor like this?

public class Category 
{
    // Copy constructor, recursively called for each child.
    public Category(Category other)
    {
        Id = other.Id;
        Name = other.Name;
        ParentId = other.ParentId;
        Parent = other.Parent;
        // Use this copy constructor for each child too:
        Children = other.Children.Select(c => new Category(c)).ToList();
    }
    // We probably want the default constructor too.
    public Category() { }

    // Your Props...
}

Usage:

var deepCopied = zone.Categories.Select(c => new Category(c));

edited Mar 15, 2019 at 11:48

answered Mar 15, 2019 at 11:40

Seva

1,7692 gold badges19 silver badges23 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Bad Dub Over a year ago

I had already came up with a solution as this was posted. Its similar to what I have so I will make it as the answer. Thanks!

ChizT · Accepted Answer · 2019-03-15 11:59:06Z

0

Use a select recursive method like so:

public static class EnumerableExtensions
{
    public static IEnumerable<T> SelectRecursive<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> selector)
    {
        foreach (var parent in source)
        {
            yield return parent;

            var children = selector(parent);
            foreach (var child in SelectRecursive(children, selector))
                yield return child;
        }
    }
}

Then do an implementation:

var lookup = _dbContext.Categories.ToLookup(x => x.ParentId);
var parents = lookup[null].SelectRecursive(x => lookup[x.Id]).Where(c => c.ParentId == null).ToList();

answered Mar 15, 2019 at 11:59

ChizT

7273 silver badges10 bronze badges

1 Comment

Bad Dub Over a year ago

I've already read this solution on a different post and it doesn't meet the requirement I need.

Collectives™ on Stack Overflow

LINQ Select Statement to Map Entity Using Recursion

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related