store variable within linq

Question

I faced this situation today and could not find on the web what I wanted.

Look at this code,

myCollection.Select(g => new ReportLine
{
    cds = (sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)) != null ? 
               sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)).USER != null?
                  sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)).USER.USER_FIRSTNAME : "": "")
                                + " " +
          (sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)) != null ?
               sectors.Where(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)).FirstOrDefault().USER != null?
                  sectors.Where(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE)).FirstOrDefault().USER.LASTNAME : "" : "")
});

Basically "myCollection" is a list of a deep class and this request goes into it extract a first and last name and put them in an other class while checking if there is no null values.

You noticed to achieve that I checked the same thing 6 times:

sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE))

(probably painful for performance)

Does a way exists to "store" the value within the linq expression ? something like this:

myCollection.Select(g => new ReportLine
{
    cds = ((var tmp =sectors.FirstOrDefault(s => s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE))) != null ? 
               tmp.USER != null?
                  tmp.USER.USER_FIRSTNAME + "" + tmp.USER.LASTNAME: "": "")
});

Steve Danner · Accepted Answer · 2014-06-30 14:22:15Z

2

I think you're probably going to have to change to long-hand LINQ to make it happen, but you can use LINQ's let clause to assign variables in the middle of an expression.

answered Jun 30, 2014 at 14:22

Steve Danner

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3 Comments

Tomas Jansson Over a year ago

What is long-hand LINQ? I see no problem in using the fluent syntax.

Steve Danner Over a year ago

See the link in the answer for an example. It's a more verbose, SQL-ish way to write the same expressions.

Tomas Jansson Over a year ago

I know what the regular linq syntax is, and the let clause, I just thought you meant something else when you wrote long-hand LINQ, since I've never heard it before. But why did you thought he had to change to that syntax?

Tomas Jansson · Accepted Answer · 2014-06-30 14:28:35Z

1

Try this:

myCollection.Select(g => { 
    var sect_code = g.Contract.Station.Sector.SECT_CODE;
    var sector = sectors.FirstOrDefault(s => s.SECT_CODE.Equals(sect_code));
    var firstName = sector != null ? 
        (sector.USER != null ? sector.USER.USER_FIRSTNAME: "") : 
        "";
    var lastName = sector != null ? 
        (sector.USER != null ? sector.USER.LASTNAME : "") : 
        "";
    return new ReportLine
    {
        cds = string.Format("{0} {1}", firstName, lastName)
    };
});

answered Jun 30, 2014 at 14:28

Tomas Jansson

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2 Comments

Servy Over a year ago

Pretty sure that EF won't be able to properly translate that.

Tomas Jansson Over a year ago

@Servy, why not? That is standard linq? Do you mean because it won't be able to lookup Contract then Station and Sector? If you ask me that is not the above linq that is the problem, rather it is EF, if used, and that he has a really nested structure in the expression.

PulseLab · Accepted Answer · 2014-06-30 14:23:13Z

-1

You could extract the logic in the Select statement to a separate method, and call that inside the Select statement?

Something like...

private string Foo(Sector input)
{
    var tmp = g.SECT_CODE.Equals etc etc
    return tmp.USER != null ? etc etc
}

...

myCollection.Select(g => Foo(g))

answered Jun 30, 2014 at 14:23

PulseLab

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8 Comments

Servy Over a year ago

If you make this change then EF won't be able to parse the code to translate it into SQL.

PulseLab Over a year ago

Was it specified that this was a SQL call?

Servy Over a year ago

The question is tagged as EF.

PulseLab Over a year ago

You're not necessarily interacting with SQL even if you're using EF.

Servy Over a year ago

But the expressions do need to be parseable, and this isn't going to allow for that.

|

user3505782 · Accepted Answer · 2014-06-30 14:33:45Z

-1

myCollection.Select(g => { var temp=sectors.FirstOrDefault(); ...

return new ReportLine(){..};

})

edited Jun 30, 2014 at 14:33

answered Jun 30, 2014 at 14:26

user3505782

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Comments

Robert Fricke · Accepted Answer · 2014-06-30 14:40:07Z

-1

This should be what you are looking for:

myCollection.Select(g => new ReportLine
{
    cds =  (from s in sectors
            where s.SECT_CODE.Equals(g.Contract.Station.Sector.SECT_CODE) && s.USER != null
            select string.Format("{0} {1}", s.USER.USER_FIRSTNAME, s.USER.USER_LASTNAME)).FirstOrDefault() ?? " "
});

answered Jun 30, 2014 at 14:40

Robert Fricke

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