Replace single node in c# tree

Question

I have a tree construct in my application which contains hierarchical data of users.

public class User {
     //a lot of properties here like Id, Name, Last Name, etc.
     public IEnumerable<User> Employees {get;set;}
}

Now I need to replace certain record in this tree with new item.

var changedUsers = GetChangedUsers();
// Replace all changed user fields in original hierarchy 
// (only FirstName, LastName, etc. without touching Employees field)

Is there an elegant way to achieve this?

EDIT:

I have tried to loop with recursion, but stuck with updating record.

private void ReplaceUserInHierarchy(User modifiedUser, List<User> users)
        {
            foreach (var user in users)
            {
                if (user.Id == modifiedUser.Id)
                {
                    //we should update here somehow
                    return;
                }

                ReplaceUserInHierarchy(modifiedUser, user.Employees);
            }
        }

What degree of elegance is required? Is flattening hierarchy and editing each matched user elegant enough? — Sergey Berezovskiy
– Sergey Berezovskiy, Commented Jul 10, 2017 at 12:36
@Gab exactly. Your question missing the main part - code which shows your attempt to solve this task and description of problem (error or incorrect results) which you can't solve — Sergey Berezovskiy
– Sergey Berezovskiy, Commented Jul 10, 2017 at 12:42

Sergey Berezovskiy · Accepted Answer · 2017-07-10 13:26:58Z

2

Simply update user wich matched given id:

private void ReplaceUserInHierarchy(User modifiedUser, List<User> users)
{
    foreach (var user in users)
    {
        if (user.Id == modifiedUser.Id)
        {
            // update properties of user here
            user.FirstName = modifiedUser.FirstName;
            // etc
            return; // if user can be duplicated in hierarchy, then use continue here
        }

        // assume user cannot be in own employees hierarchy
        ReplaceUserInHierarchy(modifiedUser, user.Employees);
    }
}

Improving elegance - you can use extension method which flattens hierarchy. Then search for the user you should update will look like:

var user = users.Flatten(u => u.Employees).FirstOrDefault(u => u.Id == modifiedUser.Id);
if (user != null) // you can throw if user not found
    user.FirstName = modifiedUser.FirstName; // etc

Flattening can be done as

public static IEnumerable<T> Flatten<T>(
   this IEnumerable<T> source,
   Func<T, IEnumerable<T>> selector)
{
   // null-check arguments
   foreach(var item in source)
   {
       yield return item;
       foreach(var child in Flatten(selector(item), selector))
           yield return child;
   }   
}

Further improvements - you can save flattened hierarchy to the dictionary and use it to update several users:

var usersById = users.Flatten(u => u.Employees).ToDictionary(u => u.Id);
foreach(var modifiedUser in modifiedUsers)
{
    User user;
    if (!usersById.TryGetValue(modifiedUser.Id, out user);)
       continue; // or throw

    user.FirstName = modifiedUser.FirstName; // etc  
}

Further improvements - you can use some library like AutoMapper to do the mapping automatically.

edited Jul 10, 2017 at 13:26

answered Jul 10, 2017 at 12:56

Sergey Berezovskiy

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9 Comments

Gab Over a year ago

Is there a way I can say to replace all properties except Employees? (there are about 30 properties)

Henk Holterman Over a year ago

Note the last s in GetChangedUsers();, your code only caters for one.

Henk Holterman Over a year ago

@Gab - sounds like you need to look at AutoMapper or similar.

Sergey Berezovskiy Over a year ago

@HenkHolterman my code changes all references of user which have id of modifiedUser

Gab Over a year ago

Still I think I need to use "return" instead of "continue" - There can be only single user with specified Id in hierarchy.

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