Thursday, March 26, 2015

How To: Convert Flat List to Hierarchical data with LINQ

Hello Readers,

Its been a long time, I have posted something.

Today I bring to you a way to generate Hierarchical data from a flat list. This method can be useful when you want to retrieve whole data with a single Stored Procedure call and while binding you need to Bind it Hierarchy based on a parent child relationship.

I have created a Generic Method, which will accept Source and Key.

public static List<TSource> AsHierarchy<TSource, TKey>(this List<TSource> collection,
Func<TSource, TKey> parentSelector, Func<TSource, TKey> childSelector, Expression<Func<TSource, List<TSource>>> childrenPropertySelector, TKey selectedKey = default(TKey))
    where TKey : struct
    if (collection != null)
        Func<TSource, bool> whereClause = x => childSelector(x).Equals(selectedKey);
        var items = collection.Where(whereClause).ToList();
        foreach (var item in items)
            var childrenProperty = (childrenPropertySelector.Body as MemberExpression).Member as System.Reflection.PropertyInfo;
            childrenProperty.SetValue(item, collection.AsHierarchy<TSource, TKey>(parentSelector, childSelector, childrenPropertySelector, parentSelector(item)), null);
        return items;
        return collection;

This method will be available as Extension Method to you List Collection. As parent selector, you need to identify what will be the key to select as parent. For childSelector you need to specify how to identify the child records. For Child Property Selector, you need to specify the property in which your child records will be saved.

For Example,

public class Employee
    public int Id {get;set;}
    public string Name {get;set;}
    public int ManagerID {get;set;}
    public List<Employee> SubOrdinates{get;set;}

Now to use the method I will write as below.

// Write your logic to get data
List<Employee> employees = GetEmployees();

//Once you have the data
List<Employee> hierarchy = employees.AsHierarchy(parent=>parent.Id, child=>child.ManagerID, parent=>parent.SubOrdinates);


Bingo!! your Hierarchical data is ready.

Try out this method and let me know if you face any issue. Post your feedback in the comments.

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