Error while converting datatable to array[] using linq

Question

I am trying to convert from datatable to array[] using linq and then join that array in one string using string.join.

Here is the code:

string.Join("','", dt
  .Select("IsCount = '1'")
  .OfType<DataRow>()
  .Select(dr => dr.Field<string>(0))
  .ToArray())

But it gives error like:

Expression cannot contain lambda expressions

.ToArray() is redundant in the context, since string.Join accepts IEnumerable<T> — Dmitrii Bychenko
– Dmitrii Bychenko, Commented Apr 24, 2017 at 12:38
The error you see is from the debugger. What is the actual problem? — Tim Schmelter
– Tim Schmelter, Commented Apr 24, 2017 at 12:39
Cannot reproduce the problem. What NET version are you using? — Steve
– Steve, Commented Apr 24, 2017 at 12:41
Think this could help stackoverflow.com/questions/23470607/… — Srikanth
– Srikanth, Commented Apr 24, 2017 at 12:44
@Tim Schmelter actual error is cannot perform '=' operation on System.Boolean and System.String. — Abdul Wahid
– Abdul Wahid, Commented Apr 24, 2017 at 12:46

Tim Schmelter · Accepted Answer · 2017-04-24 13:06:39Z

0

The reason for the error is that you compare a bool column with the string "1". That doesn't work in DataTable.Select. You can look how the syntax works and what it supports in DataColumn.Expression:

Boolean literals are true and false; they are not quoted in expressions.

So this would work:

string result = string.Join("','", dt
  .Select("IsCount = true")
  .Cast<DataRow>()
  .Select(dr => dr.Field<string>(0))); // no need for ToArray with NET 4

But instead of the strange and old Select syntax, why don't you use only LINQ?

string result = string.Join("','", dt.AsEnumerable()
  .Where(row => row.Field<bool>("IsCount"))
  .Select(row => row.Field<string>(0)));

answered Apr 24, 2017 at 13:06

Tim Schmelter

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