c# - Grouping By subproperty -

orderitems can have or not have preferences. want group orderitems preference.but preference of 1 type(4) otherwise should belong @ "null" group.

this code works other coders telling me sucks (but dont suggest solution) . ?

public ienumerable<igrouping<preference,orderitem>> orderitemsgrouped {      {          var grouped = orderitems             .groupby(item =>             {               var = item.preferences.firstordefault(p => p.preference.preferencegroup.type == 4);               if (i != null) return i.preference;               else               {                   return null;               }             })             .orderby(k => { return k.key == null ? -1 : k.key.order; });          return grouped;     }   } 

we don't know static type of orderitem.preferences.first() -- though should preference right, code looks it's not (i pulled orderitem.preferences, has preference instead of being one).

even though looks wrong, 'm going ignore , assume type of i foobar on. going treat foobar having properties preference , order, code implies.

the straightforward solution create dummy foobar object , use placeholder:

var placeholder = new foobar() { preference = null, order = -1 }; 

then body of method simplified to

return orderitems        .groupby(item => item.preferences.firstordefault(p =>                                           p.preference.preferencegroup.type == 4)                         ?? placeholder)        .orderby(g => g.key.order); 

of course changes return value in "null" group not have null key, having null key bad idea start because of semantics. if "null group" models something, make placeholder static readonly field consumers can check against it.