Select single column from dataset with LINQ

Question

Just getting my head around all this LINQ stuff and it seems I'm stuck at the first hurdle.

I have a datatable as such:

OrderNo     LetterGroup Filepath
----------- ----------- --------------------------------------------------
0           0           Letters/SampleImage.jpg
0           0           Letters/UKPC7_0.jpg
0           0           Letters/UKPC8_0.jpg

What I need is to get all of the filepaths from the Filepath column into a String array. I thought LINQ would be perfect for this (am I right?), but can't seem to construct the correct query.

Can anyone provide some code samples that would point me in the right direction? I have searched around - but don't seem to be getting anywhere.

score 34 · Accepted Answer · answered Dec 13 '10 at 20:56

34

There are extension methods which make working with data sets much easier:

using System.Data.Linq;

var filePaths =
    from row in dataTable.AsEnumerable()
    select row.Field<string>("Filepath");

var filePathsArray = filePaths.ToArray();

You can also use the method syntax to put it in one statement:

var filePaths = dataTable
    .AsEnumerable()
    .Select(row => row.Field<string>("Filepath"))
    .ToArray();

answered Dec 13 '10 at 20:56

Bryan Watts

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Why am I getting 'dataTable does not contain a definition for "Field"'? – Spero Jun 09 '19 at 20:05
@Spero: That sounds like a missing extension method. Did you include this? `using System.Data.Linq;` – Bryan Watts Jun 10 '19 at 02:38
Thx for the response. I added the necessary assembly and include, but the error is still there. I am pulling the data from DbContext though, not DataSet. I dunno how to use DataSet in Linq yet. – Spero Jun 10 '19 at 09:25
I found this:https://stackoverflow.com/questions/27738238/convert-dbcontext-to-datatable-in-code-first-entity-framework Is this necessary? – Spero Jun 10 '19 at 09:28
It seems what I am looking for is closer to this question: https://stackoverflow.com/questions/20069154/how-can-i-select-just-two-columns-from-a-list-using-linq – Spero Jun 10 '19 at 10:18
@Spero: This answer only applies to usages of `DataSet`. If you are using `DbContext`, there will be ways to do this there. Don't convert your `DbContext` to `DataSet` just to use this answer. – Bryan Watts Jun 10 '19 at 14:46
Thx for the suggestion. Tim Schmelter's answer in the other thread worked for me. – Spero Jun 10 '19 at 15:18

score 12 · Answer 2 · answered Dec 13 '10 at 20:51

12

string[] filePaths = (from DataRow row in yourDataTable.Rows 
                     select row["Filepath"].ToString()).ToArray();

answered Dec 13 '10 at 20:51

Anthony Pegram

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This isn't using LINQ at all. – poindexter12 Dec 13 '10 at 20:59
2

@poindexter12 - What? Sure looks like LINQ to me. – John Farrell Dec 13 '10 at 21:01
@jfar: This is technically LINQ syntax, so I removed my down vote. However, in the spirit the question, I think there was a little more that could be explained. – poindexter12 Dec 13 '10 at 21:03
@poindexter, the OP asked how to utilize LINQ to query his dataset, he did not ask how to completely revamp his data access strategy. This is certainly a classic use of LINQ-to-Objects. You would have him go to a LINQ-to-Entities (or equivalent) model. – Anthony Pegram Dec 13 '10 at 21:05
I agree on all counts, I would have him go LINQ to Sql. – poindexter12 Dec 13 '10 at 21:08

poindexter12 · Answer 3 · 2010-12-13T21:03:55.400

If you want to use LINQ all the way, set up your database and create a context object. Then you should be able to do something like this:

 var filepaths = from order in _context.Orders
                 select order.Filepath;

This is assuming your table for the row is named Orders, which I guess by your first column name of order. If you wanted to return a set of the order numbers as well for using later to know where the file path came from you could do something like so:

var results = from order in _context.Orders
              select new
              {
                  order.OrderNo,
                  order.Filepath
              }

This would give you a new anonymous type that contained both those values as properties.

Select single column from dataset with LINQ

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