LINQ 查询（Lambda 表达式）和 String.Join

Question

How to write a Strng.Join for this type of LINQ query(Lambda expression)? (var b will return number of integer lists)

1.

var b = braughtForwardInvoices
    .Where(x => x.LinkedTransaction != null 
             && x.LinkedTransaction.Count > 0)
    .Select(x => x.LinkedTransaction.Select(x => x.TransactionId))
    .ToList();

Below show the actual working query. I need to write the code in number 1 like number 2.

2.

var braughtForwardPaymentId = 
    from item in braughtForwardInvoices
   where item.LinkedTransaction != null 
      && item.LinkedTransaction.Count > 0
  select string.Join(",", item.LinkedTransaction.Select(x => x.TransactionId)).ToString();

Answer 1

Take the list and send it to string.Join.

var b = braughtForwardInvoices.Where(x => x.LinkedTransaction != null 
                                       && x.LinkedTransaction.Count > 0)
                              .Select(x => x.LinkedTransaction.Select(x => x.TransactionId))
                              .ToList();


var result = string.Join(",", b);

Answer 2

If you just need the selected IDs as a CSV string, you can join the resulting IEnumerable :

var b = string.Join(", ", braughtForwardInvoices.Where(x => x.LinkedTransaction != null 
                                           && x.LinkedTransaction.Count > 0)
                                  .Select(x => x.LinkedTransaction.Select(x => x.TransactionId)));