Conditional Where in Linq using query syntax

Question

Is there a better way to have conditional where clauses in LINQ equivalent to the following?

var doGroup=false; var doSub=true; var query= from mydata in Data_Details where ((doGroup && mydata.Group == "xxxx") || (doGroup==false)) && ((doSub && mydata.SubGroup == "yyyy") || (doSub==false)) select mydata;

In the code above that works it will optionally include 'Group' and 'SubGroup' depending on whether doGroup and doSub are true are false.

I know when using method syntax you can simply keep appending code to the query in separate lines but I'd prefer to keep using query syntax.

thanks I couldn't think of what linq syntax was called, and yes I did mean fluent. But what does Martin Fowler know, Fluid sounds better ;-) — Neil Walker
– Neil Walker, Commented Aug 22, 2018 at 9:59
I've always called it method syntax and that's what MS calls it. learn.microsoft.com/en-us/dotnet/csharp/programming-guide/… — juharr
– juharr, Commented Aug 22, 2018 at 11:16

Ruud Kobes · Accepted Answer · 2018-08-21 16:43:24Z

The easiest way to make this smaller is by optimizing the conditions themselves:

var doGroup=false; var doSub=true; var query=from mydata in Data_Details where (!doGroup || mydata.Group == "xxxx") && (!doSub || mydata.SubGroup == "yyyy") select mydata;

Thanks. I didn't know whether there was a way to simply append to the query on multiple lines then call 'Select' as you would with the fluent interface.

koryakinp · Accepted Answer · 2018-08-21 16:50:47Z

You can write an extension method:

public static IQueryable<T> WhereIf<T>( this IQueryable<T> source, bool condition, Expression<Func<T, bool>> predicate) { if (condition) return source.Where(predicate); else return source; }

Usage:

var doGroup =false; var doSub = true; var query = Data_Details .WhereIf(doGroup, q => q.Group == "xxxx") .WhereIf(doSub, e => e.SubGroup == "yyyy")

Thanks, I never knew about extension methods. I don't know why it was negged. But for my purpose I'll stick with the simpler way in this instance :)

elfranchu · Accepted Answer · 2018-08-24 09:17:40Z

Ruud Kobes answer is the right one, a small point at which there is not need to project data, last select is not needed.

var doGroup=false; var doSub=true; var query=from mydata in Data_Details where (!doGroup || mydata.Group == "xxxx") && (!doSub || mydata.SubGroup == "yyyy");

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