Convert LINQ method syntax with method withing .Select() to LINQ query syntax

Question

I currently have the following code:

dataSource.Where(row => row.Value == 1)
          .Select(row => {row["Text"] = translatedText; return row;})
          .Single();

So my goal is to select the DataRow with "Value=1" and at the same time set the value in the "Text"-column to some other value (in my case a string-variable transalatedText).

This already works fine with the method chain mentioned above but I generally prefer the LINQ syntax. Is there a possibility to translate this method chain to LINQ?

My problem is that I do not know how to translate the function in the Select-method to LINQ-format. I dont want to create a new DataRow but want to really edit the selected one. (So I don't want to use from x in y where z select new DataRow(...) but to really edit my x if possible)

Thanks!

Jon Skeet · Accepted Answer · 2015-04-09 15:05:02Z

2

Is there a possibility to translate this method chain to LINQ?

(By "to LINQ" I believe you mean "to query expression syntax".)

Not directly, no. Effectively, you can only convert expression-bodied lambda expressions into query syntax. There's a good reason for that: LINQ is designed not to have side effects, whereas your "query" does have side-effects.

I would personally write your code like this instead:

var row = DataSource.Single(row => row.Value == 1);
row["Text"] = translatedText;

That neatly separates the querying from the side-effect. If you really, really want to use query expression syntax, you could write:

var query = (from row in DataSource
             where row.Value == 1)
             select HorribleMutatingMethod(row)).Single();
...

private DataRow HorribleMutatingMethod(DataRow row)
{
    row["Text"] = translatedText;
    return row;
}

... but please don't.

edited Apr 9, 2015 at 15:05

answered Apr 9, 2015 at 15:03

Jon Skeet

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1 Comment

Markus Weninger Over a year ago

Yeah, i mean "query expression syntax", thanks for that. Your solution works fine for my case, but I wanted to keep the question as "general" as possible (eg. a renaming with Where(row => new []{1, 2, 3}.Contains(row.Value))

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