c# - Flatten a list which one of its properties is another list of object

Question

I have the following classes:

public class Owner
{
    public string Id { get; set; }
    public string Name { get; set; }
}
public class Main
{
    public string Id { get; set; }
    public string Name { get; set; }
    public List<Owner> Owners { get; set; }
}

I want to convert List<Main> to List<FlatList> where FlatList is

public class FlatList
{
        public string Id { get; set; }          // Id from Main
        public string Name { get; set; }        // Name from Main
        public string OwnerId { get; set; }     // Id from each Owner in a Main's Owner
        public string OwnerName { get; set; }   // Name from each Owner in a Main's Owner
}

Unfortunately I haven't been able to figure out the LinQ query to perform this operation.

Answer 1

You should use SelectMany to flatten a sequence of Main objects:

Projects each element of a sequence to an IEnumerable and flattens the resulting sequences into one sequence.

So it projects each Main object into sequence of FlatList objects and then flattens resulting sequences into one FlatList sequence

var flatList = mainList.SelectMany(m => 
    m.Owners.Select(o => 
        new FlatList { 
              Id = m.Id, 
              Name = m.Name, 
              OwnerId = o.Id,
              OwnerName = o.Name
         })).ToList()