foreach from IQueryable procedure in linq

Question

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hi everybody i have a problem with linq :
i have a class and into my class there is a precedure as IQueryable return
in procedure there is a simple join with linq and i have a foreach.

C#

public static class Class1
{
	public static IQueryable Testlinq()
	{
		var db = new DataClassesDataContext();
		var query = from tit in db.titles
			   join autit in db.titleauthors 
                           on tit.title_id equals autit.title_id
			   select new
			{
			   tit.publisher,
			   tit.price,
			   autit.author
			};
		foreach (var item in query)
		{
		  var tmp = item.author + " " + item.price + " " + item.publisher;
		}
		return query;
	}
	
}

foreach worked perfect here. but copy of this foreach to another file for examlpe default.aspx.cs doesn't work:

C#

var query = Class1.Testlinq();
		foreach (var item in query)
		{
		 var tmp = item.author + " " + item.price + " " + item.publisher;
		}

author and price and publisher are unknown here .
what must do i these items are known here?
thanks in advance

Posted 6-Feb-12 21:39pm

bafekr

Updated 6-Feb-12 21:40pm

v2

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4 solutions

Solution 2

Hi,

You can't do that. Method can't return anonymous type.

Create class with author, publisher and price properties and then return them from your method.
That way your method will return known type and all will work.
Define class:

C#

public class YourClass
{
	public string Publisher {get; set;}
	public string Author {get; set;}
	public int Price {get; set;}
}

And change method to select and return your defined type:

C#

public static class Class1
{
	public static IQueryable<yourclass> Testlinq()
	{
		// ...
		select new YourClass
		{
	            Publisher = tit.publisher,
		    Price = tit.price,
		    Author = autit.author
		};
		foreach (var item in query)
		{
		  var tmp = item.author + " " + item.price + " " + item.publisher;
		}
		return query;
	}
	
}

Maybe there are some syntax errors but you will get the point...

Posted 6-Feb-12 22:09pm

Martin Arapovic

Updated 11-Feb-12 7:44am

v2

Solution 1

try this code

C#

    var query = Class1.Testlinq();

    foreach (var item in query)
{
   item.author = item.author + " " + item.price + " " + item.publisher;
}

HTML

 the item.author is replaced with this 
(item.author + " " + item.price + " " + item.publisher;)

 example output is
 
 zyck 100.00 sample2012

Posted 6-Feb-12 22:04pm

zyck

Updated 6-Feb-12 22:05pm

v2

Solution 4

Just for the sake of completeness:

you might use the dynamic "type" here. Kind of last resort, if you can not change the interface to something more appropriate as suggested in Solution #2 and #3 of this thread.

C#

foreach (dynamic item in query)
{
    var tmp = item.author + " " + item.price + " " + item.publisher;
}

You will expereience a performance drop here:
Each member access to the dynamic variable item will inspect the type and search for the requested member before executing it!

That's why last resort ;-)

Cheers

Andi

Posted 7-Feb-12 8:51am

Andreas Gieriet

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Amir Mahfoozi · Accepted Answer · 2012-02-06T22:21:00

You should not return anonymous types from Testlinq

Please read my answer at this page :
I have a problem in Linq to SQL to return a query? in method[^]

And then make the helper class and return IEnumerable<helperclassname></helperclassname> from your Testlinq() method.

You will have access to the HelperClass fields in your foreach body then.

Hope it helps.