c# LINQ Query

Question

I have the following code:

var tableID = from data in studyData.Tables["MX_MD_TABLE"].AsEnumerable() where data.Field<string>("table_name").ToLower() == "mbddx_study_set" select data.Field<long>("ID").ToString(); string tableID = tableID.ElementAt(0).ToString();

It works as expected and the tableID is what I want. Is there a way for the LINQ query to actually return and store the returned string in as it's value, rather than having to create another object to hold it? I know that this query and a few others I will be doing, will only return the single string.

Thanks.

That code shouldn't compile - tableID is being declared twice. — RQDQ
– RQDQ, Commented Apr 6, 2011 at 13:21
@RQDQ, Correct - I changed that for the purposes of this question to make it clear in context. — Darren Young
– Darren Young, Commented Apr 6, 2011 at 13:24

Grant Thomas · Accepted Answer · 2011-04-06 13:26:56Z

This might be what you want (note the use of FirstOrDefault):

var tableID = (from data in studyData.Tables["MX_MD_TABLE"].AsEnumerable() where data.Field<string>("table_name").ToLower() == "mbddx_study_set" select data.Field<long>("ID").ToString()).FirstOrDefault();

This will select the first element found in the table that falls within the desired criteria, as opposed to returning a collection; the ID's of elements ought to be unique anyway so you should only ever be looking for a single one, I'd suspect.

Note that it also returns the value as it's expected type as defined by Field<long>, so at this point you just need to call ToString on tableID after checking it returned something - but don't append it to the FirstOrDefault call as that could return null.

Bala R · Accepted Answer · 2011-04-06 13:25:03Z

string tableID = (from data in studyData.Tables["MX_MD_TABLE"].AsEnumerable() where data.Field<string>("table_name").ToLower() == "mbddx_study_set" select data.Field<long>("ID").ToString()).ElementAt(0).ToString();

topspin · Accepted Answer · 2011-04-06 13:39:19Z

tbls.AsEnumerable().Single(o => o.Field<string>("table_name") == "value").Field<long>("ID").ToString();

Although I question your use of LINQ on a datatable to return a scalar value.

Edit:

LINQ is great and useful and very powerful, but also very expensive. DataTables have their own built-in way to search for data and return results.

See http://msdn.microsoft.com/en-us/library/y06xa2h1(v=VS.100).aspx on MSDN for an example.

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