Question

I’m trying to do use linq in a way to avoid doing a foreach over DataRows in a DataSet:

var results = from dataRow in DataRows
              let MoreData = func(dataRow.ID)
              join moreDataRow in MoreData on dataRow.ID2 = moreDataRow.ID2
              select new
              {
                  ID1 = dataRow.ID,
                  ID2 = dataRow.ID2,
                  ID3 = dataRow2.ID3
              };

I’d like to accomplish something like the above, but linq cannot use the MoreData as part of the join statement. If I’m unable to do that I may result to just doing a foreach on DataRows and going from there.

Is there a linqy way to join on data that won’t be available until iterating over an element and then performing a join from the original data to the newly generated data as above?

Answer 1

A join clause has to take a complete collection – not something which depends on the current row. You can use multiple from statements though:

var results = from dataRow in DataRows
              from moreDataRow in func(dataRow.ID)
              where dataRow.ID2 == moreDataRow.ID2
              select new
              {
                  ID1 = dataRow.ID,
                  ID2 = dataRow.ID2,
                  ID3 = dataRow2.ID3
              };