c# - Can I use FirstOrDefault() or First() inside Where() -

i trying implement query:

 data.where(d => d.objectsa != null &&     d.objectsa.first().objectsb != null &&     d.objectsa.first().objectsb().first().nr == 1) 

in nhibernate.linq, have error. when delete first() where() work. try solution don't need.

 data.where(d => d.objectsa.where(a.objectsb.where(b=>b.nr == 1).any()).any()); 

can use firstordefault() or first() inside where() ?

edit : in db tables rows in example don't have null values.

first() throw exception if collection empty. using any() in where() call should indeed solve problem, have write like:

data.where(d => d.objectsa != null && d.objectsa.any()     && d.objectsa.first().objectsb != null && d.objectsa.first().objectsb.any()     && d.objectsa.first().objectsb.first().nr == 1); 

that's not nice, because first() ends being called several times on same data. i'd suggest adding body lambda expression , using intermediate variables firstordefault():

data.where(d => {     if (d.objectsa != null) {         var firsta = d.objectsa.firstordefault();         if (firsta != null && firsta.objectsb != null) {             var firstb = firsta.objectsb.firstordefault();             if (firstb != null) {                 return (firstb.nr == 1);             }         }     }     return false; }); 

edit: second code fragment above apparently not work linq nhibernate. if can use query syntax , don't have check if objectsa , objectsb null, can write:

from d in data let firsta = d.objectsa.firstordefault() let firstb = (firsta != null ? firsta.objectsb.firstordefault() : null) (firstb != null && firstb.nr == 1) select d;