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void DoSomething()
{
   foreach (var d in Data)
   {
      if (MustDo(d.Code))
      {
         // do it!
      }
   }
}
bool MustDo(string code)
{
   if (BigCondition)
   {
     return GetData(code)?.Should ?? false;
   }
   return false;
}
AData GetData(string code) => Data.FirstOrDefault(x => x.Code == code);

void DoSomething()
{
   foreach (var d in Data)
   {
      if (BigCondition && d.Should)
      {
         // do it!
      }
   }
}