Writing elegant LINQ queries using lamda expressions

Here's what I've been able to gather from your requirements.

1. You need to put the userId condition on every property (FirstName, LastName, Email, etc.,)

2. You need to use First() or FirstOrDefault() on each of the sub-linq statements.

A snippet looks like below. FYI, I've not tried this anywhere.

Arun

IQueryable userDetails = from u in db.telerik_UserMetaInfos
                         where u.UserId == userID
                         select new
                         {
                            FirstName = (from f in db.telerik_UserMetaInfos
                                         where f.PropertyName == "FirstName"
                                            && f.UserId = userID
                                         select f.Text).FirstOrDefault(),
                            LastName = (from l in db.telerik_UserMetaInfos
                                        where l.PropertyName == "LastName"
                                            && l.UserId = userID
                                        select l.Text).FirstOrDefault()
                         };

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You are quite right, the query should look this this.

It still seems like a pretty long-winded way of doing it.  Is this the correct approach?

IQueryable userDetails = from ud in db.telerik_UserMetaInfos
                                     where ud.UserId == userID
                                     select new
                                     {
                                         FirstName = (from u in db.telerik_UserMetaInfos
                                                      where u.PropertyName == "FirstName"
                                                      && u.UserId == userID
                                                      select u.Text).First(),
                                         LastName = (from u in db.telerik_UserMetaInfos
                                                     where u.PropertyName == "LastName"
                                                     && u.UserId == userID
                                                     select u.Text).First(),
                                         Email = (from u in db.telerik_Users
                                                  where u.UserId == userID
                                                  select u.Email).First(),
                                         JobTitle = (from u in db.telerik_UserMetaInfos
                                                     where u.PropertyName == "JobTitle"
                                                     && u.UserId == userID
                                                     select u.Text).First(),
                                         DirectPhone = (from u in db.telerik_UserMetaInfos
                                                        where u.PropertyName == "DirectPhone"
                                                        && u.UserId == userID
                                                        select u.Text.First()),
                                         MobilePhone = (from u in db.telerik_UserMetaInfos
                                                        where u.PropertyName == "MobilePhone"
                                                        && u.UserId == userID
                                                        select u.Text).First(),
                                         FaxNumber = (from u in db.telerik_UserMetaInfos
                                                      where u.PropertyName == "FaxNumber"
                                                      && u.UserId == userID
                                                      select u.Text).First(),
                                         Address1 = (from u in db.telerik_UserMetaInfos
                                                     where u.PropertyName == "Address1"
                                                     && u.UserId == userID
                                                     select u.Text).First(),
                                         Address2 = (from u in db.telerik_UserMetaInfos
                                                     where u.PropertyName == "Address2"
                                                     && u.UserId == userID
                                                     select u.Text.First()),
                                         City = (from u in db.telerik_UserMetaInfos
                                                 where u.PropertyName == "City"
                                                 && u.UserId == userID
                                                 select u.Text).First(),
                                         Country = (from u in db.telerik_UserMetaInfos
                                                    where u.PropertyName == "Country"
                                                    && u.UserId == userID
                                                    select u.Text.First()),
                                         Postcode = (from u in db.telerik_UserMetaInfos
                                                     where u.PropertyName == "Postcode"
                                                     && u.UserId == userID
                                                     select u.Text).First(),
                                     };

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This is where Pivot is to be used. Pivot is to transform row values into columns; in your case values of PropertyName field (FirstName, LastName, etc) has to become columns/fields. T-SQL has built-in PIVOT function; But currently LINQ does not have built-in pivot feature (I think)...But the following links does some kind of pivoting:

This link provides LINQ extension method for pivot => http://www.reflectionit.nl/Blog/PermaLinke3b1a10d-cd24-4810-a4bf-a4285b74dbb6.aspx

http://stackoverflow.com/questions/963491/pivot-data-using-linq

So pivoting is the way for this...

Depending upon your answer based on the below articles, I would change First() to FirstOrDefault().

http://stackoverflow.com/questions/1024559/when-to-use-first-and-when-to-use-firstordefault-with-linq
http://codeforeternity.com/blogs/technology/archive/2008/04/25/linq-first-and-firstordefault-methods.aspx

Basically, if you're SURE that there's at least one element, use First(). If not, use FirstOrDefault().

And this is the only way I can think of doing this.

Arun

Hi (again!) Fernando,

I am getting a compliation error on all the .Select(fn = fn.Text).First() on each line

e.g. "fn does not exist in the current context."

OP, your code really doesn't make any sense to me.  First you are looking for a
from u in db.telerik_UserMetaInfos
                                     where u.UserId == userID
which means you are looking for a particular user, hence you got the 'u'

But then in your select, you never use that 'u' at all, instead you do a bunch of other queries.  And they are queries that return IEnumerable (collections) of what I assume is strings:

FirstName = (from f in db.telerik_UserMetaInfos
                                                      where f.PropertyName == "FirstName"
                                                      select f.Text)

is returnnin ALL of the telerik_UserMetaInfo items that PropertyName == "FirstnName" not just the ones where u.UserId == userId.

I think you need to take a look at your original code as I assume it really isn't working as you would like.

Fernando:  that fixed that issue, but now it errors on }).FirstOrDefault(); - "Cannot implicitly convert type "AnonymousType#1' to System.Linq.IQueryable.  

If I remove ).FirstOrDefault() it compiles, or if I change IQueryable to type var.  

Should I use var?

Okay, I see.  Thanks!  Can someone recommend a good Lamda resource?

Try this link:

Lambda Expressions (C# Programming Guide)
http://msdn.microsoft.com/en-us/library/bb397687.aspx

The solution was exactly what I was looking for.  Thanks.

Not a problem, glad I was able to help.  ;=)