c# - Immediate Window and runtime giving different results for same LINQ statement -

i have piece of code compares 2 collections, , returns items 1 list doesn't belong in other.

as these 2 lists contain objects aren't equitable reference, have simple iequatable compares objects on ids.

the code running follows:

private preferencedefinition[] finduserpreferencestoadd(preferencedefinition[] newdefinitions, preferencedefinition[] olddefinitions) {      //get newly selected definitions      var newpreferences = newdefinitions.where(def => def.isselected);       //get new definitions don't exist in old list      var preferencestoadd = newpreferences.where(def => !olddefinitions.contains(def)).toarray();       return preferencestoadd; } 

the result of preferencestoadd gives me exact same list in newpreferences, despite purposely ensuring newdefinitions contains additional item has been selected. if pass in 7 new preferences, return 7 preferences 'add' - incorrect implementation.

however, when run exact same linq statement in immediate window when hit breakpoint on return, gives me:

newpreferences.where(def => !olddefinitions.contains(def)).toarray(); {app1test.preferencedefinition[1]}     [0]: {app1test.preferencedefinition} 

this contains single result should added.

why immediate window give me correct result, run time code wouldn't? tried running statement in immediate window before , after runtime linq query ran ensure wasn't order of operations thing, made no difference.

edit:

i have found solution issue, replacing second linq statement with:

var preferencestoadd = newpreferences.where(d => !olddefinitions.any(def => def.equals(d))).toarray();

however don't understand why original did not work. have similar scenario opposite of i'm trying achieve here (find items delete), , works fine. missing something?

edit 2:

this code, without iequatable, worked fine:

private preferencedefinition[] finduserpreferencestodelete(preferencedefinition[] newdefinitions, preferencedefinition[] olddefinitions) {     //get newly selected definitions      var newpreferences = newdefinitions.where(def => def.isselected);       //get old definitions don't exist in new list      var preferencestodelete = olddefinitions.where(def => !newpreferences.contains(def));       return preferencestodelete.toarray(); } 

why work fine, first method wouldn't?

have here:

https://msdn.microsoft.com/en-us/library/ms131187(v=vs.110).aspx

if implement iequatable, should override base class implementations of object.equals(object) , gethashcode behavior consistent of iequatable.equals method.

you can deduct == operator not affected implementing iequatable;

therefore equals call uses custom equality method , contains internally use object.equals not overridden.

the array implements icollection therefore contains method used internally implemented in array indexof without using equalitycomparer.default tries use iequatable.equals if any.

try adding this:

public override bool equals(object obj) {     var test = obj test;      return test == null ? obj.equals(this) : equals(test); } 

you can see simple example here: https://dotnetfiddle.net/c5r4be