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).

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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);

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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.

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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;
}

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What about:

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