Max return value if empty query

Question

I have this query:

int maxShoeSize = Workers
    .Where(x => x.CompanyId == 8)
    .Max(x => x.ShoeSize);

What will be in maxShoeSize if company 8 has no workers at all?

UPDATE:
How can I change the query in order to get 0 and not an exception?

Answer 1

int maxShoeSize = Workers.Where(x => x.CompanyId == 8)
                         .Select(x => x.ShoeSize)
                         .DefaultIfEmpty(0)
                         .Max();

The zero in DefaultIfEmpty is not necessary.

Answer 2

I know this is an old question and the accepted answer works, but this question answered my question about whether such an empty set would result in an exception or a default(int) result.

The accepted answer however, while it does work, isn't the ideal solution IMHO, which isn't given here. Thus I am providing it in my own answer for the benefit of anyone who is looking for it.

The OP's original code was:

int maxShoeSize = Workers.Where(x => x.CompanyId == 8).Max(x => x.ShoeSize);

This is how I would write it to prevent exceptions and provide a default result:

int maxShoeSize = Workers.Where(x => x.CompanyId == 8).Max(x => x.ShoeSize as int?) ?? 0;

This causes the return type of the Max function to be int?, which allows the null result and then the ?? replaces the null result with 0.

---

EDIT
Just to clarify something from the comments, Entity Framework doesn't currently support the as keyword, so the way to write it when working with EF would be:

int maxShoeSize = Workers.Where(x => x.CompanyId == 8).Max<[TypeOfWorkers], int?>(x => x.ShoeSize) ?? 0;

Since the [TypeOfWorkers] could be a long class name and is tedious to write, I've added an extension method to help out.

public static int MaxOrDefault<T>(this IQueryable<T> source, Expression<Func<T, int?>> selector, int nullValue = 0)
{
    return source.Max(selector) ?? nullValue;
}

This only handles int, but the same could be done for long, double, or any other value type you need. Using this extension method is very simple, you just pass in your selector function and optionally include a value to be used for null, which defaults to 0. So the above could be rewritten like so:

int maxShoeSize = Workers.Where(x => x.CompanyId == 8).MaxOrDefault(x => x.ShoeSize);

Hopefully that helps people out even more.

Answer 3

Max() won't return anything in that case.

It will raise InvalidOperationException since the source contains no elements.

Answer 4

int maxShoeSize = Workers.Where(x => x.CompanyId == 8)
                     .Select(x => x.ShoeSize)
                     .DefaultIfEmpty()
                     .Max();

Answer 5

If this is Linq to SQL, I don't like to use Any() because it results in multiple queries to SQL server.

If ShoeSize is not a nullable field, then using just the .Max(..) ?? 0 will not work but the following will:

int maxShoeSize = Workers.Where(x = >x.CompanyId == 8).Max(x => (int?)x.ShoeSize) ?? 0;

It absolutely does not change the emitted SQL, but it does return 0 if the sequence is empty because it changes the Max() to return an int? instead of an int.

Answer 6

int maxShoeSize=Workers.Where(x=>x.CompanyId==8)
    .Max(x=>(int?)x.ShoeSize).GetValueOrDefault();

(assuming that ShoeSize is of type int)

If Workers is a DbSet or ObjectSet from Entity Framework your initial query would throw an InvalidOperationException, but not complaining about an empty sequence but complaining that the materialized value NULL can't be converted into an int.

Answer 7

NB: the query with DefaultIfEmpty() may be significantly slower. In my case that was a simple query with .DefaultIfEmpty(DateTime.Now.Date).

I was too lazy to profile it but obviously EF tried to obtain all the rows and then take the Max() value.

Conclusion: sometimes handling InvalidOperationException might be the better choice.

Answer 8

Max will throw System.InvalidOperationException "Sequence contains no elements"

class Program
{
    static void Main(string[] args)
    {
        List<MyClass> list = new List<MyClass>();

        list.Add(new MyClass() { Value = 2 });

        IEnumerable<MyClass> iterator = list.Where(x => x.Value == 3); // empty iterator.

        int max = iterator.Max(x => x.Value); // throws System.InvalidOperationException
    }
}

class MyClass
{
    public int Value;
}

Answer 9

You can use a ternary within .Max() to handle the predicate and set its value;

// assumes Workers != null && Workers.Count() > 0
int maxShoeSize = Workers.Max(x => (x.CompanyId == 8) ? x.ShoeSize : 0);

You would need to handle the Workers collection being null/empty if that's a possibility, but it would depend on your implementation.

Answer 10

You can try this:

int maxShoeSize = Workers.Where(x=>x.CompanyId == 8).Max(x => x.ShoeSize) ?? 0;

Answer 11

You could check if there are any workers before doing the Max().

private int FindMaxShoeSize(IList<MyClass> workers) {
   var workersInCompany = workers.Where(x => x.CompanyId == 8);
   if(!workersInCompany.Any()) { return 0; }
   return workersInCompany.Max(x => x.ShoeSize);
}