LINQ select from TList?

I have a list of RowData items (a custom class).

A RowData item contains a list of CellData items (another custom class).

Currently, the only way I can access each individual CellData item is through the RowData's this[int index], which means I'd h开发者_如何转开发ave to create a loop for each search.

What I want is to create a method that will return all of the CellData items for a given index value:

private List<RowData> rowList;

public IEnumerable<CellData> Cells(int index) {
  foreach (var row in rowList) {
    if (row.ID == index) {
      return row.AsEnumerable<CellData>();
    }
  }
  return null;
}

I don't like returning NULL, and I'd like to know how to accomplish this task using some LINQ techniques (either Query or Method syntax).

To be able to use LINQ syntax for getting cells collection from row, your RowData need to be enumerable, i.e. implement IEnumerable interface.

By .AsEnumerable<CellData>() in your example, I assume your RowData already implements it and enumerating RowData returns collection of CellData objects.

If not, you need to implement IEnumerable in RowData on your own. If your this[int index] accessor reads the data from a collection, you can just return that collection's GetEnumerator.

And then, you'll be able to fetch CellData collection from RowData collection using LINQ queries, i.e. like this:

var cells = rowList.Where(x => x.ID == index).SelectMany(x => x);

Assuming only one row is returned given an index:

public IEnumerable<CellData> Cells(int index) 
{
    var foundRow = rowList.FirstOrDefault(row => row.ID == index);
    //if no row was found, foundRow will be null
    if(foundRow != null)
        return foundRow.AsEnumerable<CellData>();
    else
        return new CellData[]; //return empty cells IEnumerable. Could also be new List<CellData>()
    }
}

This code assumes foundRow.AsEnumerable<CellData>() returns a IEnumerable<CellData>.

You have to check for nullity, because row at a given index might nor be found.

This will achieve the same result.

 var resultsList = from x in rowList
                      where x.ID == index
                      select x;
 return resultsList;

public IEnumerable<CellData> Cells(int index){
    var cells = (from r on rowList
                where r.ID == index
                select r.Cells).FirstOrDefault();
    return cells;
}

What about:

List<CellData> cells = rowList.Where(x => x.Index == index).SelectMany(x => x.Cells).ToList();