从列表中的两个不同对象返回LINQ select查询中的特定对象

Question

I have a list that could contain eg. the following objects

ObjectFirst {
id = 1;
mode = Constants.Active;
}

ObjectSecond {
id = 2;
mode = Constants.Passive;
}

How can I make a LINQ query that selects the object with "mode = Constants.Active" if that exists and if not it selects the object with the "mode = Constants.Passive"? Only one object should be returned. I would like to solve this with one LINQ query.

Answer 1

I am not sure if that could be done in one query but it could be done in multiple ways, You can try:

var obj = list.Any(r=> r.mode == Constants.Active) ? 
                            list.FirstOrDefault(r=> r.mode == Constants.Active)
                            list.FirstOrDefault(r=> r.mode == Constants.Passive);

Or:

var obj = list.FirstOrDefault(r=> r.mode == Constants.Active);
if(obj == null)
{
   obj = list.FirstOrDefault(r=> r.mode == Constants.Passive);
}

Answer 2

In theory you could order them by the mode , thus giving them a priority, and then return the first. Assuming that Constants.Active is lower than Constants.Passive .

var obj = list.OrderBy(r => r.mode).FirstOrDefault()

Optionally, you could add some extra checking:

var obj = list.Where(r => r.Id == someId).OrderBy(r => r.mode).FirstOrDefault()